Cressida is an inner satellite of the planet Uranus.
Cressida is the 11th largest Moon of Uranus and the 54th largest moon in the Solar System currently known.
Discovery
Cressida was discovered by Stephen P. Synnott, who is an American astronomer and Voyager scientist, from the images taken by Voyager 2 on 9 January 1986.
Naming
The moon was given the temporary designation S/1986 U3.
Cressida the moon was named after the Trojan daughter of Calchas, a tragic heroine who appears in William Shakespeare's play Troilus and Cressida (as well as in tales by Geoffrey Chaucer and others).
Cressida is a character who appears in many Medieval and Renaissance retellings of the story of the Trojan War. She is a Trojan woman, the daughter of Calchas, a priestly defector to the Greeks. She falls in love with Troilus the youngest son of King Priam, and pledges everlasting love, but when she is sent to the Greeks as part of a hostage exchange, she forms a liaison with the Greek warrior Diomedes.
Stats
Diameter (mean): 79.6 km
Semi-major axis: 61,766 km
Orbital Period: 0.464 days
Orbit
Cressida takes as long to rotate on its axis as it does to make one orbit of Uranus; and therefore always keeps the same hemisphere pointed to Uranus.
Cressida belongs to a group of satellites called the Portia Group, which includes Portia, Bianca, Belinda, Desdemona, Rosalind, Cupid, Juliet and Perdita. These satellites have similar orbits and photometric properties.
Cressida may collide with Desdemona within the next 100 million years.
Physical characteristics
Little is known about Cressida beyond its size of about 80 km, orbit and geometric albedo of about 0.08.
The Voyager 2 images show Cressida as an elongated object with its major axis pointing towards Uranus. The ratio of axes of the Cressida's prolate spheroid is 0.8 ± 0.3. Cressida's surface is grey in color.
Exploration Status
No close-up image of Cressida has been photographed.
No mission is planned in the foreseeable future.
Tuesday 28 February 2012
Sunday 26 February 2012
11th Largest Moon of Saturn - Epimetheus (6th Moon outwards from Saturn)
Epimetheus is an inner moon of Saturn and it is co-orbital with another moon Janus.
Epimetheus is the 11th largest moon of Saturn, and the 44th largest moon in the Solar System currently known.
Discovery
Epimetheus occupies practically the same orbit as the moon Janus. This caused some confusion for astronomers, who assumed that there was only one body in that orbit, and for a long time struggled to figure out what was going on. It was eventually realized that they were trying to reconcile observations of two distinct objects as a single object.
Audouin Charles Dollfus observed a moon on December 15, 1966, which he proposed to be named "Janus". On December 18, Richard Walker made a similar observation which is now credited as the discovery of Epimetheus. However, at the time, it was believed that there was only one moon, unofficially known as "Janus", in the given orbit.
Twelve years later, in October 1978, Stephen M. Larson and John W. Fountain realised that the 1966 observations were best explained by two distinct objects (Janus and Epimetheus) sharing very similar orbits. This was confirmed in 1980 by Voyager 1, and so Larson and Fountain officially share the discovery of Epimetheus with Richard Walker.
Naming
Epimetheus received its name in 1983, when it is named after the mythological Epimetheus, brother of Prometheus.
In Greek mythology, Epimetheus ("hindsight", literally "afterthought,") was the brother of Prometheus ("foresight", literally "fore-thought"), a pair of Titans who "acted as representatives of mankind". They were the inseparable sons of Iapetus, who in other contexts was the father of Atlas. While Prometheus is characterized as ingenious and clever, Epimetheus is depicted as foolish.
Stats
Diameter (mean): 116 km
Semi-major axis: 151,410 km
Orbital Period: 0.694 days
Co-orbital moons
Epimetheus and Janus share their orbits, the difference in semi-major axes being less than either's mean diameter. This means the moon with the smaller semi-major axis will slowly catch up with the other. As it does this, the moons gravitationally tug at each other, increasing the semi-major axis of the moon that has caught up and decreasing that of the other.
This reverses their relative positions (proportionally to their masses) and causes this process to begin anew with the moons' roles reversed. In other words, they effectively swap orbits, ultimately oscillating both about their mass-weighted mean orbit.
Epimetheus rotates synchronously with its orbital period, keeping one face pointed toward Saturn.
Formation
Epimetheus and Janus may have formed from a disruption of a single parent to form co-orbital satellites, but if this is the case the disruption must have happened early in the history of the satellite system.
Physical characteristics
There are several Epimethean craters larger than 30 km in diameter, as well as both large and small ridges and grooves. The extensive cratering indicates that Epimetheus must be quite old.
The south pole shows what might be the remains of a large impact crater covering most of this face of the moon, and which could be responsible for the somewhat flattened shape of the southern part of Epimetheus.
There appear to be two terrain types: darker, smoother areas, and brighter, slightly more yellowish, fractured terrain. One interpretation is that the darker material evidently moves down slopes, and probably has a lower ice content than the brighter material, which appears more like "bedrock". Nonetheless, materials in both terrains are likely to be rich in water ice.
From its very low density and relatively high albedo, it seems likely that Epimetheus is a very porous icy body. There is a lot of uncertainty in these values, however, and so this remains to be confirmed.
Ring
A faint dust ring is present around the region occupied by the orbits of Epimetheus and Janus, as revealed by images taken in forward-scattered light by the Cassini spacecraft in 2006.
The ring has a radial extent of about 5000 km. Its source is particles blasted off the moons' surfaces by meteoroid impacts, which then form a diffuse ring around their orbital paths.
Thursday 23 February 2012
11th Largest Moon of Jupiter - Metis (1st Moon outwards from Jupiter)
Metis has an irregular shape and measures 60×40×34 km across, which makes it the second smallest of the four inner satellites of Jupiter.
Metis is the 11th largest moon of Jupiter and 69th largest moon in the Solar System currently known.
Discovery
Metis was discovered in 4 March 1979 by Stephen P. Synnott in images taken by the Voyager 1 probe.
The photographs taken by Voyager 1 showed Metis only as a dot, and hence knowledge about Metis was very limited until the arrival of the Galileo spacecraft. Galileo imaged almost all of the surface of Metis and put constraints on its composition by 1998.
Naming
Metis was provisionally designated as S/1979 J3. In 1983 it was officially named after the mythological Metis, a Titaness who was the first wife of Zeus (the Greek equivalent of Jupiter).
In Greek mythology, Metis was of the Titan generation and, like several primordial figures, an Oceanid, in the sense that Metis was born of Oceanus and Tethys, of an earlier age than Zeus and his siblings. Metis was the first great spouse of Zeus.
By the era of Greek philosophy in the fifth century BCE, Metis had become the goddess of wisdom and deep thought.
Stats
Diameter (mean): 43 km
Semi-major axis: 127,690 km
Orbital Period: 0.295 day
Orbit
Metis orbits Jupiter at a distance of ~128,000 km (1.79 Jupiter radii) within the planet's main ring.
Due to tidal locking, Metis rotates synchronously with its orbital period, with its longest axis aligned towards Jupiter.
Metis lies inside Jupiter's synchronous orbit radius, and as a result, tidal forces slowly cause its orbit to decay, and the moon will eventually impact Jupiter. If its density is similar to Amalthea's, Metis' orbit lies within the fluid Roche limit; however, since it has not broken up, it must lie outside its rigid Roche limit.
Relationship with Jupiter's rings
Metis' orbit lies ~1000 km within the main ring of Jupiter. It orbits within a ~500 km wide "gap" or "notch" in the ring. The gap is clearly somehow related to the moon but the origin of this connection has not been established.
Metis supplies a significant part of the main ring’s dust. This material appears to consist primarily of material that is ejected from the surfaces of Jupiter's four small inner satellites by meteorite impacts. It is easy for the impact ejecta to be lost from the satellites into space because the satellites' surfaces lie fairly close to the edge of their Roche spheres due to their low density.
Physical Characteristics
The bulk composition and mass of Metis are not known, but assuming that its mean density is like that of Amalthea (~0.86 g/cm³), its mass can be estimated as ~3.6×1016 kg. Metis' density implies that that moon is composed of water ice with a porosity of 10–15%.
The Metidian surface is heavily cratered, dark, and appears to be reddish in color. There is a substantial asymmetry between leading and trailing hemispheres: the leading hemisphere is 1.3-times brighter than the trailing one.
The asymmetry is probably caused by the higher velocity and frequency of impacts on the leading hemisphere, which excavate a bright material (presumably ice) from the interior of the moon.
Monday 20 February 2012
25th Largest Asteroid, 94 Aurora
94 Aurora is one of the largest main-belt asteroids and is the 25th largest asteroid currently known.
Discovery
Aurora was discovered by James Craig Watson on September 6, 1867, in Ann Arbor, Michigan, USA.
Naming
The asteroid was named after Aurora, the Roman goddess of the dawn.
In Roman mythology, Aurora, goddess of the dawn, renews herself every morning and flies across the sky, announcing the arrival of the sun.
Stats
Diameter (mean): 205 km
Aphelion: 3.435 AU
Perihelion: 2.878 AU
Semi-major axis: 3.16 AU
Orbital Period: 5.62 years
Rotation period: 7.22 hrs
Date discovered: 1867.9.6
Class: C
Type: Main-belt Asteroid
(data from JPL Small-Body Database)
Physical Characteristics
With an albedo of only 0.04, Aurora is darker than soot, and has a primitive compositions consisting of carbonaecous material.
Star Occultation
Observations of an occultation (TYC 6910-01938-1) on October 12, 2001, using nine chords indicate an oval outline of 225×173 km.
Discovery
Aurora was discovered by James Craig Watson on September 6, 1867, in Ann Arbor, Michigan, USA.
Naming
The asteroid was named after Aurora, the Roman goddess of the dawn.
In Roman mythology, Aurora, goddess of the dawn, renews herself every morning and flies across the sky, announcing the arrival of the sun.
Stats
Diameter (mean): 205 km
Aphelion: 3.435 AU
Perihelion: 2.878 AU
Semi-major axis: 3.16 AU
Orbital Period: 5.62 years
Rotation period: 7.22 hrs
Date discovered: 1867.9.6
Class: C
Type: Main-belt Asteroid
(data from JPL Small-Body Database)
Physical Characteristics
With an albedo of only 0.04, Aurora is darker than soot, and has a primitive compositions consisting of carbonaecous material.
Star Occultation
Observations of an occultation (TYC 6910-01938-1) on October 12, 2001, using nine chords indicate an oval outline of 225×173 km.
Sunday 19 February 2012
24th Largest Asteroid, 13 Egeria
Egeria is the 24th largest asteroid currently known.
Discovery
Egeria was discovered by Annibale de Gasparis on 2 November 1850, in Naples.
Naming
Egeria was named by Urbain J. J. Le Verrier, whose computations led to the discovery of Neptune.
Egeria was a nymph attributed a legendary role in the early history of Rome as a divine consort and counselor of the Sabine second king of Rome, Numa Pompilius, to whom she imparted laws and rituals pertaining to ancient Roman religion. Her name is used as an eponym for a female advisor or counselor.
Stats
Diameter (mean): 208 km
Aphelion: 2.794 AU
Perihelion: 2.359 AU
Semi-major axis: 2.578 AU
Orbital Period: 4.14 years
Rotation period: 7.045 hrs
Date discovered: 1850.11.2
Class: G
Type: Main-belt Asteroid
(data from JPL Small-Body Database)
Physical Characteristics
Spectral analysis of Egeria shows it to be unusually high in water content, between 10.5-11.5% water by mass. This makes Egeria a prominent candidate for future water-mining ventures.
Star Occultation
Egeria occulted a star on January 8, 1992. The former's disc was determined to be quite circular (217×196 km).
On January 22, 2008, Egeria occulted another star (TYC 0026-00627-1) and this occultation was timed by several observers in New Mexico and Arizona, coordinated by the IOTA Asteroid Occultation Program.
The data was entered into the OCCULT4 estimation and visualization program written by Dave Herald of Canberra, Australia. The result showed that Egeria presented an approximately circular profile to Earth of 214.8x192 km, well in agreement with the 1992 occultation.
23th Largest Asteroid, 423 Diotima
423 Diotima is a one of the largest main-belt asteroids.
Diotima is the 23th largest asteroid currently known.
Discovery
Diotima was discovered by Auguste Honoré Charlois on December 7, 1896, in Nice.
Naming
It is named for a priestess who was one of Socrates's teachers. It is one of seven of Charlois's discoveries that was expressly named by the Astromomisches Rechen-Institut (Astronomical Calculation Institute).
Diotima of Mantinea is a female seer who plays an important role in Plato's Symposium. Her ideas are the origin of the concept of Platonic love. Since the only source concerning her is Plato, it is uncertain whether she was a real historical personage or merely a fictional creation. However, nearly all of the characters named in Plato's dialogues have been found to correspond to real people living in ancient Athens.
In Plato's Symposium the members of a party discuss the meaning of love. Socrates says that in his youth he was taught "the philosophy of love" by Diotima, who was a seer or priestess. Socrates also claims that Diotima successfully postponed the plague of Athens.
Stats
Diameter (mean): 209 km
Aphelion: 3.191 AU
Perihelion: 2.949 AU
Semi-major axis: 3.069 AU
Orbital Period: 5.38 years
Rotation period: 4.775 hrs
Date discovered: 1896.12.7
Class: C
Type: Main-belt Asteroid
(data from JPL Small-Body Database)
Physical Characteristics
Diotima is classified as a C-type asteroid and is probably composed of primitive carbonaceous material.
Diotima is the 23th largest asteroid currently known.
Discovery
Diotima was discovered by Auguste Honoré Charlois on December 7, 1896, in Nice.
Naming
It is named for a priestess who was one of Socrates's teachers. It is one of seven of Charlois's discoveries that was expressly named by the Astromomisches Rechen-Institut (Astronomical Calculation Institute).
Diotima of Mantinea is a female seer who plays an important role in Plato's Symposium. Her ideas are the origin of the concept of Platonic love. Since the only source concerning her is Plato, it is uncertain whether she was a real historical personage or merely a fictional creation. However, nearly all of the characters named in Plato's dialogues have been found to correspond to real people living in ancient Athens.
In Plato's Symposium the members of a party discuss the meaning of love. Socrates says that in his youth he was taught "the philosophy of love" by Diotima, who was a seer or priestess. Socrates also claims that Diotima successfully postponed the plague of Athens.
Stats
Diameter (mean): 209 km
Aphelion: 3.191 AU
Perihelion: 2.949 AU
Semi-major axis: 3.069 AU
Orbital Period: 5.38 years
Rotation period: 4.775 hrs
Date discovered: 1896.12.7
Class: C
Type: Main-belt Asteroid
(data from JPL Small-Body Database)
Physical Characteristics
Diotima is classified as a C-type asteroid and is probably composed of primitive carbonaceous material.
22th Largest Asteroid, 29 Amphitrite
Amphitrite is the 22th largest asteroid currently known.
Discovery
Amphitrite was discovered by Albert Marth on March 1, 1854, at the private South Villa Observatory, in Regent's Park, London. It was Marth's only asteroid discovery.
Naming
The asteroid's name was chosen by George Bishop, the owner of the observatory, who named it after Amphitrite, a sea goddess in Greek mythology.
In ancient Greek mythology, Amphitrite was a sea-goddess and wife of Poseidon. Under the influence of the Olympian pantheon, she became merely the consort of Poseidon, and was further diminished by poets to a symbolic representation of the sea.
Stats
Diameter (mean): 212 km
Aphelion: 2.739 AU
Perihelion: 2.369 AU
Semi-major axis: 2.555 AU
Orbital Period: 4.08 years
Rotation period: 5.392 hrs
Date discovered: 1854.3.1
Class: S
Satellite: 1 ?
Type: Main-belt Asteroid
(data from JPL Small-Body Database)
Orbit
Amphirite's orbit is less eccentric and inclined than those of its larger cousins; indeed, it has one of the most circular of asteroid orbits.
Amphirite can reach magnitudes of around +8.6 at a favorable opposition, but usually is around the binocular limit of +9.5.
Satellite
A satellite of the asteroid is suspected based on lightcurve data collected by Edward F. Tedesco.
Saturday 18 February 2012
Moons of asteroid 45 Eugenia -- (45) Eugenia II S/2004 (45) 1
Eugenia is orbited by two small moons. They have been named Petit-Prince and provisional designated S/2004(45)1 [(45) Eugenia I Petit-Prince and (45) Eugenia II S/2004(45)1].
(45) Eugenia II S/2004(45)1 is the smaller, inner moon of asteroid 45 Eugenia. Nothing much is known about this moon.
Discovery
S/2004(45)1 was discovered by F. Marchis, M. Baek, P. Descamps, J. Berthier, D. Hestroffer and F. Vachier on analyses of three images acquired in 14 February 2004 using the adaptive optics from the 8.2 m VLT "Yepun" at the European Southern Observatory (ESO) Cerro Paranal, in Chile.
Naming
The moon received the provisional designation S/2004(45)1.
Stats
Diameter (estimated): 6 km
Semi-major axis: 700 km ?
Orbital Period: 2 days ?
Rotation period: ?
(45) Eugenia II S/2004(45)1 is the smaller, inner moon of asteroid 45 Eugenia. Nothing much is known about this moon.
Discovery
S/2004(45)1 was discovered by F. Marchis, M. Baek, P. Descamps, J. Berthier, D. Hestroffer and F. Vachier on analyses of three images acquired in 14 February 2004 using the adaptive optics from the 8.2 m VLT "Yepun" at the European Southern Observatory (ESO) Cerro Paranal, in Chile.
Naming
The moon received the provisional designation S/2004(45)1.
Stats
Diameter (estimated): 6 km
Semi-major axis: 700 km ?
Orbital Period: 2 days ?
Rotation period: ?
Friday 17 February 2012
Moons of asteroid 45 Eugenia -- (45) Eugenia I Petit-Prince
Eugenia is orbited by two small moons. They have been named Petit-Prince and provisional designated S/2004(45)1 [(45) Eugenia I Petit-Prince and S/2004(45)1].
(45) Eugenia I Petit-Prince is the larger, outer moon of asteroid 45 Eugenia.
Discovery
Petit-Prince was discovered in 1 Nov 1998 by a group of astronomers (W. J. Merline, L. M. Close, C. Dumas, C. R. Chapman, F. Roddier, F. Menard, D. C. Slater, G. Duvert, J. C. Shelton, T. Morgan) at the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii.
Petit-Prince was the first asteroid moon to be discovered with a ground-based telescope. Petit-Prince is much smaller than Eugenia, about 13 km in diameter, and takes five days to complete an orbit around it.
Naming
Initially, the moon received the provisional designation S/1998(45)1.
The discoverers chose the name in honour of Empress Eugénie's son, the Prince Imperial, because the moon orbits an asteroid named after his mother (45 Eugenia).
Napoléon, Prince Imperial, (Full name: Napoléon Eugène Louis Jean Joseph, 16 March 1856, Paris – 1 June 1879), Prince Imperial, was the only child of Emperor Napoleon III of France and his Empress consort Eugénie de Montijo. His early death in Africa sent shock waves throughout Europe.
However, they also intended an allusion to the children's book The Little Prince by Antoine de Saint-Exupery, which is about a prince who lives on an asteroid (Asteroid B-612).
The Little Prince (French: ''Le Petit Prince''), first published in 1943, is a novella and the most famous work of the French aristocrat writer, poet and pioneering aviator Antoine de Saint-Exupéry (1900–1944).
Stats
Diameter (estimated): 13 km
Semi-major axis: 1184 ± 12 km
Orbital Period: 4.77 days
Rotation period: ?
(45) Eugenia I Petit-Prince is the larger, outer moon of asteroid 45 Eugenia.
Discovery
Petit-Prince was discovered in 1 Nov 1998 by a group of astronomers (W. J. Merline, L. M. Close, C. Dumas, C. R. Chapman, F. Roddier, F. Menard, D. C. Slater, G. Duvert, J. C. Shelton, T. Morgan) at the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii.
Petit-Prince was the first asteroid moon to be discovered with a ground-based telescope. Petit-Prince is much smaller than Eugenia, about 13 km in diameter, and takes five days to complete an orbit around it.
Naming
Initially, the moon received the provisional designation S/1998(45)1.
The discoverers chose the name in honour of Empress Eugénie's son, the Prince Imperial, because the moon orbits an asteroid named after his mother (45 Eugenia).
Napoléon, Prince Imperial, (Full name: Napoléon Eugène Louis Jean Joseph, 16 March 1856, Paris – 1 June 1879), Prince Imperial, was the only child of Emperor Napoleon III of France and his Empress consort Eugénie de Montijo. His early death in Africa sent shock waves throughout Europe.
However, they also intended an allusion to the children's book The Little Prince by Antoine de Saint-Exupery, which is about a prince who lives on an asteroid (Asteroid B-612).
The Little Prince (French: ''Le Petit Prince''), first published in 1943, is a novella and the most famous work of the French aristocrat writer, poet and pioneering aviator Antoine de Saint-Exupéry (1900–1944).
Stats
Diameter (estimated): 13 km
Semi-major axis: 1184 ± 12 km
Orbital Period: 4.77 days
Rotation period: ?
Wednesday 15 February 2012
21th Largest Asteroid, 45 Eugenia
45 Eugenia is a large main belt asteroid, with a diameter of 215 km. Eugenia is the 21th largest asteroid currently known.
Discovery
Eugenia was discovered on June 27, 1857 by the Franco-German amateur astronomer Hermann Goldschmidt. His instrument of discovery was a 4-inch aperture telescope located in his sixth floor apartment in the Latin Quarter of Paris.
Eugenia was the forty-fifth asteroid to be discovered. The preliminary orbital elements were computed by Wilhelm Forster in Berlin, based on three observations in July, 1857.
Naming
The asteroid was named by its discoverer Hermann Goldschmidt after Empress Eugenia di Montijo, the wife of Napoleon III.
Eugenia was the first asteroid to be definitely named after a real person, rather than a figure from classical legend.
Stats
Diameter (mean): 214.6 km
Aphelion: 2.943 AU
Perihelion: 2.50 AU
Semi-major axis: 2.724 AU
Orbital Period: 4.49 years
Rotation period: 5.699 hrs
Date discovered: 1857.6.27
Class: F
Satellite: 2
Type: Main-belt Asteroid
(data from JPL Small-Body Database)
Physical characteristics
Eugenia is an F-type asteroid, which means that it is very dark in colouring (darker than soot) with a carbonaceous composition.
Eugenia's density appears to be unusually low, indicating that it may be a loosely-packed rubble pile, not a monolithic object. Eugenia appears to be almost anhydrous.
Satellite system
Eugenia is famed as one of the first asteroids to be found to have a moon orbiting it. It is also the second known triple asteroid, after 87 Sylvia.
Discovery
Eugenia was discovered on June 27, 1857 by the Franco-German amateur astronomer Hermann Goldschmidt. His instrument of discovery was a 4-inch aperture telescope located in his sixth floor apartment in the Latin Quarter of Paris.
Eugenia was the forty-fifth asteroid to be discovered. The preliminary orbital elements were computed by Wilhelm Forster in Berlin, based on three observations in July, 1857.
Naming
The asteroid was named by its discoverer Hermann Goldschmidt after Empress Eugenia di Montijo, the wife of Napoleon III.
Eugenia was the first asteroid to be definitely named after a real person, rather than a figure from classical legend.
Stats
Diameter (mean): 214.6 km
Aphelion: 2.943 AU
Perihelion: 2.50 AU
Semi-major axis: 2.724 AU
Orbital Period: 4.49 years
Rotation period: 5.699 hrs
Date discovered: 1857.6.27
Class: F
Satellite: 2
Type: Main-belt Asteroid
(data from JPL Small-Body Database)
Physical characteristics
Eugenia is an F-type asteroid, which means that it is very dark in colouring (darker than soot) with a carbonaceous composition.
Eugenia's density appears to be unusually low, indicating that it may be a loosely-packed rubble pile, not a monolithic object. Eugenia appears to be almost anhydrous.
Satellite system
Eugenia is famed as one of the first asteroids to be found to have a moon orbiting it. It is also the second known triple asteroid, after 87 Sylvia.
Monday 13 February 2012
Moons of outer solar system - Hi'iaka (moon of Haumea)
Hiʻiaka is the larger, outer moon of the dwarf planet Haumea.
Hiʻiaka is a large moon and the 22th largest moon in the Solar System currently known.
Hiʻiaka is too faint to detect with telescopes smaller than about 2 metres in aperture, though Haumea itself has a visual magnitude of 17.5, making it the third brightest object in the Kuiper belt after Pluto and Makemake, and easily observable with a large amateur telescope.
Discovery
Hiʻiaka is discovered on 26 Jan 2005 by the team of Michael E. Brown, Chadwick A. Trujillo, David Lincoln Rabinowitz, etc from observations of Haumea made at the large telescopes of the W. M. Keck Observatory in Hawaii.
Naming
Initially it had gone by the nickname "Rudolph" by its discovery team, as Haumea itself is nicknamed "Santa".
Rudolph the Red-Nosed Reindeer is a reindeer with a glowing red nose. He is popularly known as "Santa's 9th Reindeer" and, when depicted, is the lead reindeer pulling Santa's sleigh on Christmas Eve. The luminosity of his nose is so great that it illuminates the team's path through inclement winter weather.
It is later officially named after one of the daughters of Haumea. Hiʻiaka is the goddess of dance and patroness of the Big Island of Hawaii, where the Mauna Kea Observatory is located.
In Hawaiian mythology, Hiʻiaka is a daughter of Haumea and Kāne. She was the patron goddess of Hawaiʻi and the hula dancers, and takes on the task of bearing the clouds - variously, those of storms and those produced by her sister's volcanos, and lived in a grove of Lehua trees which are sacred to her where she spent her days dancing with the forest spirits. She is also called Hiʻiaka-i-ka-poli-o-Pele literally meaning "Cloud bearer cradled in the bosom of Pele". Hiʻiaka was conceived in Tahiti, but carried in the form of an egg to Hawaiʻi by Pele, who kept the egg with her at all times to incubate it. Hiʻiaka is Pele's favorite and most loyal sister.
Stats
Diameter (estimated): 310 km
Semi-major axis: 49,880 km
Orbital Period: 49.12 days
Rotation Period: ?
Formation
Haumea's moons are unusual in a number of ways. They are thought to be part of its extended collisional family, which formed billions of years ago from icy debris after a large impact disrupted Haumea's ice mantle.
The dwarf planet Haumea appears to be almost entirely made of rock, with only a superficial layer of ice; most of the original icy mantle is thought to have been blasted off by the impact that spun Haumea into its current high speed of rotation, where the material formed into the small Kuiper belt objects in Haumea's collisional family and the two known Haumea moons.
Surface properties
Hiʻiaka, the larger, outermost moon, has large amounts of pure water ice on its surface, a feature rare among Kuiper belt objects.
Strong absorption features observed at 1.5, 1.65 and 2 micrometres in its infrared spectrum are consistent with nearly pure crystalline water ice covering much of its surface. The unusual spectrum, and its similarity to absorption lines in the spectrum of Haumea, led Brown and colleagues to conclude that it was unlikely that the system of moons was formed by the gravitational capture of passing Kuiper belt objects into orbit around the dwarf planet. Instead, the Haumean moons must be fragments of Haumea's ice mantle.
How big is it?
The size of Hi'iaka is calculated with the assumption that it has the same infrared albedo as Haumea, which is reasonable as the spectra show them to have the same surface composition. Haumea's albedo has been measured by the Spitzer Space Telescope and from ground-based telescopes, while Hi'iaka is too small and close to Haumea to be seen independently. Based on this common albedo, Hiʻiaka is estimated to be about 310 km in diameter.
Hiʻiaka is a large moon and the 22th largest moon in the Solar System currently known.
Hiʻiaka is too faint to detect with telescopes smaller than about 2 metres in aperture, though Haumea itself has a visual magnitude of 17.5, making it the third brightest object in the Kuiper belt after Pluto and Makemake, and easily observable with a large amateur telescope.
Discovery
Hiʻiaka is discovered on 26 Jan 2005 by the team of Michael E. Brown, Chadwick A. Trujillo, David Lincoln Rabinowitz, etc from observations of Haumea made at the large telescopes of the W. M. Keck Observatory in Hawaii.
Naming
Initially it had gone by the nickname "Rudolph" by its discovery team, as Haumea itself is nicknamed "Santa".
Rudolph the Red-Nosed Reindeer is a reindeer with a glowing red nose. He is popularly known as "Santa's 9th Reindeer" and, when depicted, is the lead reindeer pulling Santa's sleigh on Christmas Eve. The luminosity of his nose is so great that it illuminates the team's path through inclement winter weather.
It is later officially named after one of the daughters of Haumea. Hiʻiaka is the goddess of dance and patroness of the Big Island of Hawaii, where the Mauna Kea Observatory is located.
In Hawaiian mythology, Hiʻiaka is a daughter of Haumea and Kāne. She was the patron goddess of Hawaiʻi and the hula dancers, and takes on the task of bearing the clouds - variously, those of storms and those produced by her sister's volcanos, and lived in a grove of Lehua trees which are sacred to her where she spent her days dancing with the forest spirits. She is also called Hiʻiaka-i-ka-poli-o-Pele literally meaning "Cloud bearer cradled in the bosom of Pele". Hiʻiaka was conceived in Tahiti, but carried in the form of an egg to Hawaiʻi by Pele, who kept the egg with her at all times to incubate it. Hiʻiaka is Pele's favorite and most loyal sister.
Stats
Diameter (estimated): 310 km
Semi-major axis: 49,880 km
Orbital Period: 49.12 days
Rotation Period: ?
Formation
Haumea's moons are unusual in a number of ways. They are thought to be part of its extended collisional family, which formed billions of years ago from icy debris after a large impact disrupted Haumea's ice mantle.
The dwarf planet Haumea appears to be almost entirely made of rock, with only a superficial layer of ice; most of the original icy mantle is thought to have been blasted off by the impact that spun Haumea into its current high speed of rotation, where the material formed into the small Kuiper belt objects in Haumea's collisional family and the two known Haumea moons.
Surface properties
Hiʻiaka, the larger, outermost moon, has large amounts of pure water ice on its surface, a feature rare among Kuiper belt objects.
Strong absorption features observed at 1.5, 1.65 and 2 micrometres in its infrared spectrum are consistent with nearly pure crystalline water ice covering much of its surface. The unusual spectrum, and its similarity to absorption lines in the spectrum of Haumea, led Brown and colleagues to conclude that it was unlikely that the system of moons was formed by the gravitational capture of passing Kuiper belt objects into orbit around the dwarf planet. Instead, the Haumean moons must be fragments of Haumea's ice mantle.
How big is it?
The size of Hi'iaka is calculated with the assumption that it has the same infrared albedo as Haumea, which is reasonable as the spectra show them to have the same surface composition. Haumea's albedo has been measured by the Spitzer Space Telescope and from ground-based telescopes, while Hi'iaka is too small and close to Haumea to be seen independently. Based on this common albedo, Hiʻiaka is estimated to be about 310 km in diameter.
Sunday 12 February 2012
(202421) 2005 UQ513 - 12th Largest TNO? 4th Largest Cubewano ?
2005 UQ513 is a large trans-Neptunian object. 2005 UQ513 is possibly the 12th largest TNO and 4th largest Cubewano currently known.
Discovery
2005 UQ513 is discovered on 21 Oct 2005 by Michael E. Brown, Chadwick A. Trujillo and David Lincoln Rabinowitz at Palomar Observatory. 2005 UQ513 has precovery images back to 1990.
Stats
Estimated Diameter: 748 km (550 - 1240 km)
Aphelion: 49.63 AU
Perihelion: 37.0 AU
Semi-major axis: 43.31 AU
Orbital Period: 285.12 years
Rotation period: ? hours
Date discovered: 2005.10.21
Satellite: ?
Classification: TNO, KBO - Cubewano
Orbit
2005 UQ513 is currently 48.7 AU from the Sun. It will come to perihelion around 2124.
2005 UQ513 shows signs of weak water ice.
Dwarf-planet status
Michael E. Brown's automatically updated website lists 2005 UQ513 as a highly likely dwarf planet, but the diameter of the object has never been measured.
How big is it?
2005 UQ513 is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Discovery
2005 UQ513 is discovered on 21 Oct 2005 by Michael E. Brown, Chadwick A. Trujillo and David Lincoln Rabinowitz at Palomar Observatory. 2005 UQ513 has precovery images back to 1990.
Stats
Estimated Diameter: 748 km (550 - 1240 km)
Aphelion: 49.63 AU
Perihelion: 37.0 AU
Semi-major axis: 43.31 AU
Orbital Period: 285.12 years
Rotation period: ? hours
Date discovered: 2005.10.21
Satellite: ?
Classification: TNO, KBO - Cubewano
Orbit
2005 UQ513 is currently 48.7 AU from the Sun. It will come to perihelion around 2124.
2005 UQ513 shows signs of weak water ice.
Dwarf-planet status
Michael E. Brown's automatically updated website lists 2005 UQ513 as a highly likely dwarf planet, but the diameter of the object has never been measured.
How big is it?
2005 UQ513 is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
(174567) 2003 MW12 - 11th Largest TNO? 3rd Largest Cubewano ?
2003 MW12 is a large trans-Neptunian object. 2003 MW12 is possibly the 11th largest TNO and 3rd largest Cubewano currently known.
Discovery
2003 MW12 was discovered on June 21, 2003 by Jeffrey A. Larsen with the Spacewatch telescope at Kitt Peak Observatory. 2003 MW12 has precovery images back to 1980.
Stats
Estimated Diameter: 748 km (500 - 1130 km)
Aphelion: 52.28 AU
Perihelion: 39.62 AU
Semi-major axis: 45.95 AU
Orbital Period: 311.51 years
Rotation period: 5.9 hours
Date discovered: 2003.6.21
Satellite: ?
Classification: TNO, KBO - Cubewano
Orbit
2003 MW12 is currently 47.5 AU from the Sun, and will come to perihelion around November 2096.
Dwarf-planet status
Michael E. Brown's automatically updated website lists 2003 MW12 as a highly likely dwarf planet, but the diameter of the object has never been measured.
How big is it?
2003 MW12 is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Discovery
2003 MW12 was discovered on June 21, 2003 by Jeffrey A. Larsen with the Spacewatch telescope at Kitt Peak Observatory. 2003 MW12 has precovery images back to 1980.
Stats
Estimated Diameter: 748 km (500 - 1130 km)
Aphelion: 52.28 AU
Perihelion: 39.62 AU
Semi-major axis: 45.95 AU
Orbital Period: 311.51 years
Rotation period: 5.9 hours
Date discovered: 2003.6.21
Satellite: ?
Classification: TNO, KBO - Cubewano
Orbit
2003 MW12 is currently 47.5 AU from the Sun, and will come to perihelion around November 2096.
Dwarf-planet status
Michael E. Brown's automatically updated website lists 2003 MW12 as a highly likely dwarf planet, but the diameter of the object has never been measured.
How big is it?
2003 MW12 is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
(229762) 2007 UK126 - 10th Largest TNO? 3rd Largest SDO ?
((229762) 2007 UK126 is a large trans-Neptunian object. 2007 UK126 is possibly the 10th largest TNO and 3rd largest scattered disc object (SDO) currently known.
Discovery
2007 UK126 is discovered on 19 Oct 2007 by Michael E. Brown, M. E. Schwamb and David Lincoln Rabinowitz at Palomar Observatory.
Stats
Estimated Diameter: 748 km (530 - 1190 km)
Aphelion: 110.3 AU
Perihelion: 37.68 AU
Semi-major axis: 74.15 AU
Orbital Period: 638.76 years
Rotation period: ?
Date discovered: 2007.10.19
Satellite: ?
Classification: TNO, Scattered Disc Object
Orbit
2007 UK126's eccentricity of 0.49 suggests that it was gravitationally scattered onto its eccentric orbit. 2007 UK126 will come to perihelion around 2046.
Dwarf-planet status
2007 UK126 has a bright absolute magnitude of 3.4. This qualifies it as one of the largest dwarf-planet candidates. Michael E. Brown lists it as a highly likely dwarf planet.
How big is it?
2007 UK126 is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Discovery
2007 UK126 is discovered on 19 Oct 2007 by Michael E. Brown, M. E. Schwamb and David Lincoln Rabinowitz at Palomar Observatory.
Stats
Estimated Diameter: 748 km (530 - 1190 km)
Aphelion: 110.3 AU
Perihelion: 37.68 AU
Semi-major axis: 74.15 AU
Orbital Period: 638.76 years
Rotation period: ?
Date discovered: 2007.10.19
Satellite: ?
Classification: TNO, Scattered Disc Object
Orbit
2007 UK126's eccentricity of 0.49 suggests that it was gravitationally scattered onto its eccentric orbit. 2007 UK126 will come to perihelion around 2046.
Dwarf-planet status
2007 UK126 has a bright absolute magnitude of 3.4. This qualifies it as one of the largest dwarf-planet candidates. Michael E. Brown lists it as a highly likely dwarf planet.
How big is it?
2007 UK126 is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Saturday 11 February 2012
(90482) Orcus - 9th Largest TNO? 2nd Largest Plutino?
90482 Orcus is a trans-Neptunian object in the Kuiper belt with a large moon. It is considered to be a dwarf planet by some astronomers, but the IAU has not formally designated it as such.
Discovery
Orcus was discovered on February 17, 2004 by Michael E. Brown of Caltech, Chadwick A. Trujillo of the Gemini Observatory, and David Lincoln Rabinowitz of Yale University. Precovery images as early as November 8, 1951 were later identified.
Naming
Under the guidelines of the International Astronomical Union's naming conventions, objects with a similar size and orbit to that of Pluto are named after underworld deities.
Accordingly, the discoverers suggested naming the object after Orcus, a god of the underworld, punisher of broken oaths in Etruscan and Roman mythology.
The name was also a private reference to the homonymous Orcas Island, where Brown's wife Diane had lived as a child and which they visit frequently.
Stats
Estimated Diameter: 950 km (850 - 950 km)
Aphelion: 48.07 AU
Perihelion: 30.27 AU
Semi-major axis: 39.17 AU
Orbital Period: 245.18 years
Rotation period: 13.19 hrs
Date discovered: 2004.2.17
Satellite: 1
Classification: TNO, KBO - Plutino
Orbit
Orcus is a plutino, locked in a 2:3 resonance with Neptune, making two revolutions around the Sun, while Neptune makes three.
Orcus is much like Pluto, except that it is constrained to always be in the opposite phase of its orbit from Pluto: Orcus is at aphelion when Pluto is at perihelion and vice versa. Because of this, along with its large moon Vanth that recalls Pluto's large moon Charon, Orcus has been seen as the anti-Pluto.
This was a major consideration in selecting its name, as the deity Orcus was the Etruscan equivalent of the Roman Pluto, and later became an alternate name for Pluto.
The rotation period of the primary is not known. Different photometric surveys have produced different results. Some show low amplitude variations with periods ranging from 7 to 21 hours, while others show no variability. However the value obtained by Ortiz et al., about 10.5 hours seems to be the most likely.
Spectra and surface
The first spectroscopic observations in 2004 showed that the visible spectrum of Orcus is flat (neutral in color) and featureless, while in the near-infrared there were moderately strong water absorption bands at 1.5 and 2.0 μm.
Further Infrared observations in 2004 by the European Southern Observatory and the Gemini telescope give results consistent with mixtures of water ice and carbonaceous compounds, such as tholins.
The water and methane ices can cover no more than 50% and 30% of the surface, respectively. This means the proportion of ice on the surface is less than on Charon, but similar to that on Triton.
Later in 2008–2010 new infrared spectroscopic observations with a higher signal-to-noise ratio revealed additional spectral features. Among them are a deep water ice absorption band at 1.65 μm, which is an evidence of the crystalline water ice on the surface of Orcus, and a new absorption band at 2.22 μm.
The origin of the latter feature is not completely clear. It can be caused either by ammonia/ammonium dissolved in the water ice or by methane/ethane ices.
The radiative transfer modeling showed that a mixture of water ice, tholins (as a darkening agent), ethane ice and ammonium ion (NH4+) provides the best match to the spectra, while a combination of water ice, tholins, methane ice and ammonia hydrate gives a slightly inferior result.
On the other hand, a mixture of only ammonia hydrate, tholins and water ice failed to provide a satisfactory match. So, as of 2010, the only reliably identified compounds on the surface of Orcus are crystalline water ice and, possibly, dark tholins. A firm identification of ammonia, methane and other hydrocarbons requires better infrared spectra.
Cryovolcanism
The presence of crystalline water ice, and possibly ammonia ice may indicate that a renewal mechanism was active in the past on the surface of Orcus. Ammonia so far has not been detected on any TNO or icy satellite of the outer planets other than Miranda. The 1.65 μm band on Orcus is broad and deep (12%), as on Charon, Quaoar, Haumea, and icy satellites of giant planets.
On the other hand the crystalline water ice on the surfaces of TNOs should be completely amorphized by the galactic and Solar radiation in about 10 million years. Some calculations indicate that cryovolcanism, which is considered one of the possible renewal mechanisms, may indeed be possible for TNOs larger than about 1000 km.
Orcus may have experienced at least one such episode in the past, which turned the amorphous water ice on its surface into crystalline. The preferred type of volcanism may have been explosive aqueous volcanism driven by an explosive dissolution of methane from water–ammonia melts.
Models of internal heating via radioactive decay suggest that Orcus may be capable of sustaining an internal ocean of liquid water.
Moon
Using observations with the Hubble Space Telescope from November 13, 2005, Mike Brown and T.A. Suer detected a satellite. The discovery of a satellite of Orcus was reported on 22 February 2007.
The satellite was given the designation S/2005 (90482) 1 before later being named Vanth, after the Etruscan goddess who guided the souls of the dead to the underworld.
How big is it?
Orcus is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Discovery
Orcus was discovered on February 17, 2004 by Michael E. Brown of Caltech, Chadwick A. Trujillo of the Gemini Observatory, and David Lincoln Rabinowitz of Yale University. Precovery images as early as November 8, 1951 were later identified.
Naming
Under the guidelines of the International Astronomical Union's naming conventions, objects with a similar size and orbit to that of Pluto are named after underworld deities.
Accordingly, the discoverers suggested naming the object after Orcus, a god of the underworld, punisher of broken oaths in Etruscan and Roman mythology.
The name was also a private reference to the homonymous Orcas Island, where Brown's wife Diane had lived as a child and which they visit frequently.
Stats
Estimated Diameter: 950 km (850 - 950 km)
Aphelion: 48.07 AU
Perihelion: 30.27 AU
Semi-major axis: 39.17 AU
Orbital Period: 245.18 years
Rotation period: 13.19 hrs
Date discovered: 2004.2.17
Satellite: 1
Classification: TNO, KBO - Plutino
Orbit
Orcus is a plutino, locked in a 2:3 resonance with Neptune, making two revolutions around the Sun, while Neptune makes three.
Orcus is much like Pluto, except that it is constrained to always be in the opposite phase of its orbit from Pluto: Orcus is at aphelion when Pluto is at perihelion and vice versa. Because of this, along with its large moon Vanth that recalls Pluto's large moon Charon, Orcus has been seen as the anti-Pluto.
This was a major consideration in selecting its name, as the deity Orcus was the Etruscan equivalent of the Roman Pluto, and later became an alternate name for Pluto.
The rotation period of the primary is not known. Different photometric surveys have produced different results. Some show low amplitude variations with periods ranging from 7 to 21 hours, while others show no variability. However the value obtained by Ortiz et al., about 10.5 hours seems to be the most likely.
Spectra and surface
The first spectroscopic observations in 2004 showed that the visible spectrum of Orcus is flat (neutral in color) and featureless, while in the near-infrared there were moderately strong water absorption bands at 1.5 and 2.0 μm.
Further Infrared observations in 2004 by the European Southern Observatory and the Gemini telescope give results consistent with mixtures of water ice and carbonaceous compounds, such as tholins.
The water and methane ices can cover no more than 50% and 30% of the surface, respectively. This means the proportion of ice on the surface is less than on Charon, but similar to that on Triton.
Later in 2008–2010 new infrared spectroscopic observations with a higher signal-to-noise ratio revealed additional spectral features. Among them are a deep water ice absorption band at 1.65 μm, which is an evidence of the crystalline water ice on the surface of Orcus, and a new absorption band at 2.22 μm.
The origin of the latter feature is not completely clear. It can be caused either by ammonia/ammonium dissolved in the water ice or by methane/ethane ices.
The radiative transfer modeling showed that a mixture of water ice, tholins (as a darkening agent), ethane ice and ammonium ion (NH4+) provides the best match to the spectra, while a combination of water ice, tholins, methane ice and ammonia hydrate gives a slightly inferior result.
On the other hand, a mixture of only ammonia hydrate, tholins and water ice failed to provide a satisfactory match. So, as of 2010, the only reliably identified compounds on the surface of Orcus are crystalline water ice and, possibly, dark tholins. A firm identification of ammonia, methane and other hydrocarbons requires better infrared spectra.
Cryovolcanism
The presence of crystalline water ice, and possibly ammonia ice may indicate that a renewal mechanism was active in the past on the surface of Orcus. Ammonia so far has not been detected on any TNO or icy satellite of the outer planets other than Miranda. The 1.65 μm band on Orcus is broad and deep (12%), as on Charon, Quaoar, Haumea, and icy satellites of giant planets.
On the other hand the crystalline water ice on the surfaces of TNOs should be completely amorphized by the galactic and Solar radiation in about 10 million years. Some calculations indicate that cryovolcanism, which is considered one of the possible renewal mechanisms, may indeed be possible for TNOs larger than about 1000 km.
Orcus may have experienced at least one such episode in the past, which turned the amorphous water ice on its surface into crystalline. The preferred type of volcanism may have been explosive aqueous volcanism driven by an explosive dissolution of methane from water–ammonia melts.
Models of internal heating via radioactive decay suggest that Orcus may be capable of sustaining an internal ocean of liquid water.
Moon
Using observations with the Hubble Space Telescope from November 13, 2005, Mike Brown and T.A. Suer detected a satellite. The discovery of a satellite of Orcus was reported on 22 February 2007.
The satellite was given the designation S/2005 (90482) 1 before later being named Vanth, after the Etruscan goddess who guided the souls of the dead to the underworld.
How big is it?
Orcus is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
(84522) 2002 TC302 - 8th Largest TNO?
2002 TC302 is a large, red 2:5 resonant trans-Neptunian object.
Discovery
2002 TC302 is discovered on October 9, 2002, by Michael E. Brown's team at the Palomar Observatory.
Stats
Estimated Diameter: 1150 km
Aphelion: 71.87 AU
Perihelion: 39.20 AU
Semi-major axis: 55.54 AU
Orbital Period: 413.86 years
Rotation period: ? hrs
Date discovered: 2002.10.9
Satellite: ?
Classification: TNO, 2:5 resonance
Orbit
Both the Minor Planet Center (MPC) and the Deep Ecliptic Survey (DES) show this dwarf-planet candidate to be in a 2:5 resonance with Neptune. Due to the resonance, it completes 2 orbits for every 5 orbits of Neptune.
As of 2009, it is the largest dwarf-planet candidate that is known to be in a (non-plutino) resonance with Neptune.
Surface and albedo
The red spectra suggests that 2002 TC302 has very little fresh ice on its surface and may explain why it has a lower-than-average estimated albedo of ~0.03.
Large dwarf-planet candidate
2002 TC302 has an absolute magnitude (H) of 3.87, and the Spitzer Space Telescope has estimated it to have a diameter of 1145.7 ± 325 km. This qualifies it as one of the largest dwarf-planet candidates.
However, Brown notes that the measurement involves a very large potential error, and that the object is likely smaller, making its chances of being a dwarf planet "highly likely" rather than "virtually certain", as it would be if it were actually 1100 km in diameter.
How big is it?
2002 TC302 is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Discovery
2002 TC302 is discovered on October 9, 2002, by Michael E. Brown's team at the Palomar Observatory.
Stats
Estimated Diameter: 1150 km
Aphelion: 71.87 AU
Perihelion: 39.20 AU
Semi-major axis: 55.54 AU
Orbital Period: 413.86 years
Rotation period: ? hrs
Date discovered: 2002.10.9
Satellite: ?
Classification: TNO, 2:5 resonance
Orbit
Both the Minor Planet Center (MPC) and the Deep Ecliptic Survey (DES) show this dwarf-planet candidate to be in a 2:5 resonance with Neptune. Due to the resonance, it completes 2 orbits for every 5 orbits of Neptune.
As of 2009, it is the largest dwarf-planet candidate that is known to be in a (non-plutino) resonance with Neptune.
Surface and albedo
The red spectra suggests that 2002 TC302 has very little fresh ice on its surface and may explain why it has a lower-than-average estimated albedo of ~0.03.
Large dwarf-planet candidate
2002 TC302 has an absolute magnitude (H) of 3.87, and the Spitzer Space Telescope has estimated it to have a diameter of 1145.7 ± 325 km. This qualifies it as one of the largest dwarf-planet candidates.
However, Brown notes that the measurement involves a very large potential error, and that the object is likely smaller, making its chances of being a dwarf planet "highly likely" rather than "virtually certain", as it would be if it were actually 1100 km in diameter.
How big is it?
2002 TC302 is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Friday 10 February 2012
(90377) Sedna - 6th Largest TNO?
90377 Sedna is a very large trans-Neptunian object. Sedna is the 6th largest TNO currently known. Neither its mass nor its size are well known, and the IAU has not formally designated it as a dwarf planet, although it is considered to be one by several astronomers.
Discovery
Sedna was discovered by Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003. The discovery formed part of a survey begun in 2001 with the Samuel Oschin telescope at Palomar Observatory near San Diego, California using Yale's 160 megapixel Palomar Quest camera.
On that day, an object was observed to move by 4.6 arcseconds over 3.1 hours relative to stars, which indicated that its distance was about 100 AU. Follow-up observations in November–December 2003 with the SMARTS telescope at Cerro Tololo Inter-American Observatory in Chile as well as with the Tenagra IV telescope at the W. M. Keck Observatory in Hawaii revealed that the object was moving along a distant highly eccentric orbit.
Later the object was identified on older precovery images made by the Samuel Oschin telescope as well as on images from the Near Earth Asteroid Tracking consortium. These previous positions expanded its known orbital arc and allowed a more precise calculation of its orbit.
At the time of its discovery it was the largest object found in the Solar System since Pluto in 1930.
Naming
Sedna was provisionally designated 2003 VB12.
As the newly discovered object is at the coldest most distant place known in the Solar System, Mike Brown the discoverer felt it is appropriate to name it in honor of Sedna, the Inuit goddess of the sea, who is thought to live at the bottom of the frigid Arctic Ocean.
In Inuit mythology, Sedna is the goddess of the sea and marine animals such as seals. A creation myth, the story of Sedna shows how she came to rule over Adlivun, the Inuit underworld.
Stats
Diameter: 1400 km (1200 - 1600 km)
Aphelion: 937 AU
Perihelion: 76.36 AU
Semi-major axis: 518 AU
Orbital Period: 11,400 years
Rotation period: 10 hrs
Date discovered: 2003.11.14
Satellite: 0
Classification: TNO, Detached Object
Orbit
Sedna has the longest orbital period of any known large object in the Solar System, other than long-period comets, calculated at around 11,400 years. Sedna's orbit is extremely eccentric, with an aphelion estimated at 937 AU and a perihelion at about 76 AU, the most distant perihelion ever observed for any Solar System object.
At its discovery it was approaching perihelion at 89.6 AU from the Sun, and was the most distant object in the Solar System yet observed. (Eris was later detected by the same survey at 97 AU).
Physical characteristics
Sedna has an absolute magnitude (H) of 1.6, and it is estimated to have an albedo of 0.16 to 0.30, thus giving it a diameter between 1,200 and 1,600 km.
Observations from the SMARTS telescope show that in visible light Sedna is one of the reddest objects in the Solar System, nearly as red as Mars. Chad Trujillo and his colleagues suggest that Sedna's dark red colour is caused by a surface coating of hydrocarbon sludge, or tholin, formed from simpler organic compounds after long exposure to ultraviolet radiation. Its surface is homogeneous in colour and spectrum; this may be because Sedna, unlike objects nearer the Sun, is rarely impacted by other bodies, which would expose bright patches of fresh icy material.
Spectroscopy has revealed that Sedna's surface composition is similar to that of some other trans-Neptunian objects, being largely a mixture of water, methane and nitrogen ices with tholins.
The detection of methane and water ices was confirmed in 2006 by Spitzer Space Telescope mid-infrared photometry. The presence of nitrogen on the surface suggests the possibility that, at least for a short time, Sedna may possess an atmosphere. During a 200-year period near perihelion the maximum temperature on Sedna should exceed 35.6 K (−237.6 °C), the transition temperature between alpha-phase solid N2 and the beta phase seen on Triton.
However, its deep red spectral slope is indicative of high concentrations of organic material on its surface, and its weak methane absorption bands indicate that methane on Sedna's surface is ancient, rather than freshly deposited. This means that Sedna is too cold for methane to evaporate from its surface and then fall back as snow, as happens on Triton and probably on Pluto.
Models of internal heating via radioactive decay suggest that Sedna might be capable of supporting a subsurface ocean of liquid water.
Origin
Sedna's exceptionally long and elongated orbit, taking approximately 11,400 years to complete, and distant point of closest approach to the Sun, at 76 AU, have led to much speculation as to its origin.
The Minor Planet Center currently places Sedna in the scattered disc, a group of objects sent into highly elongated orbits by the gravitational influence of Neptune. However, this classification has been contested, as Sedna never comes close enough to Neptune to have been scattered by it, leading some astronomers to conclude that it is in fact the first known member of the inner Oort cloud.
Others speculate that it might have been tugged into its current orbit by a passing star, perhaps one within the Sun's birth cluster, or even that it was captured by the Sun from a passing extrasolar planetary system.
A hypothesis suggests that Sedna's orbit is the result of influence by a large binary companion to the Sun, thousands of AU distant. One such hypothetical companion is Nemesis, a dim companion to the Sun which has been proposed to be responsible for the supposed periodicity of mass extinctions on Earth from cometary impacts, the lunar impact record, and the common orbital elements of a number of long period comets. However, to date no direct evidence of Nemesis has been found, and many lines of evidence (such as crater counts), have thrown its existence into doubt.
Another hypothesis suggests that its orbit may be evidence for an as-yet-undiscovered large planet beyond the orbit of Neptune.
How big is it?
Sedna is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Discovery
Sedna was discovered by Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003. The discovery formed part of a survey begun in 2001 with the Samuel Oschin telescope at Palomar Observatory near San Diego, California using Yale's 160 megapixel Palomar Quest camera.
On that day, an object was observed to move by 4.6 arcseconds over 3.1 hours relative to stars, which indicated that its distance was about 100 AU. Follow-up observations in November–December 2003 with the SMARTS telescope at Cerro Tololo Inter-American Observatory in Chile as well as with the Tenagra IV telescope at the W. M. Keck Observatory in Hawaii revealed that the object was moving along a distant highly eccentric orbit.
Later the object was identified on older precovery images made by the Samuel Oschin telescope as well as on images from the Near Earth Asteroid Tracking consortium. These previous positions expanded its known orbital arc and allowed a more precise calculation of its orbit.
At the time of its discovery it was the largest object found in the Solar System since Pluto in 1930.
Naming
Sedna was provisionally designated 2003 VB12.
As the newly discovered object is at the coldest most distant place known in the Solar System, Mike Brown the discoverer felt it is appropriate to name it in honor of Sedna, the Inuit goddess of the sea, who is thought to live at the bottom of the frigid Arctic Ocean.
In Inuit mythology, Sedna is the goddess of the sea and marine animals such as seals. A creation myth, the story of Sedna shows how she came to rule over Adlivun, the Inuit underworld.
Stats
Diameter: 1400 km (1200 - 1600 km)
Aphelion: 937 AU
Perihelion: 76.36 AU
Semi-major axis: 518 AU
Orbital Period: 11,400 years
Rotation period: 10 hrs
Date discovered: 2003.11.14
Satellite: 0
Classification: TNO, Detached Object
Orbit
Sedna has the longest orbital period of any known large object in the Solar System, other than long-period comets, calculated at around 11,400 years. Sedna's orbit is extremely eccentric, with an aphelion estimated at 937 AU and a perihelion at about 76 AU, the most distant perihelion ever observed for any Solar System object.
At its discovery it was approaching perihelion at 89.6 AU from the Sun, and was the most distant object in the Solar System yet observed. (Eris was later detected by the same survey at 97 AU).
Physical characteristics
Sedna has an absolute magnitude (H) of 1.6, and it is estimated to have an albedo of 0.16 to 0.30, thus giving it a diameter between 1,200 and 1,600 km.
Observations from the SMARTS telescope show that in visible light Sedna is one of the reddest objects in the Solar System, nearly as red as Mars. Chad Trujillo and his colleagues suggest that Sedna's dark red colour is caused by a surface coating of hydrocarbon sludge, or tholin, formed from simpler organic compounds after long exposure to ultraviolet radiation. Its surface is homogeneous in colour and spectrum; this may be because Sedna, unlike objects nearer the Sun, is rarely impacted by other bodies, which would expose bright patches of fresh icy material.
Spectroscopy has revealed that Sedna's surface composition is similar to that of some other trans-Neptunian objects, being largely a mixture of water, methane and nitrogen ices with tholins.
The detection of methane and water ices was confirmed in 2006 by Spitzer Space Telescope mid-infrared photometry. The presence of nitrogen on the surface suggests the possibility that, at least for a short time, Sedna may possess an atmosphere. During a 200-year period near perihelion the maximum temperature on Sedna should exceed 35.6 K (−237.6 °C), the transition temperature between alpha-phase solid N2 and the beta phase seen on Triton.
However, its deep red spectral slope is indicative of high concentrations of organic material on its surface, and its weak methane absorption bands indicate that methane on Sedna's surface is ancient, rather than freshly deposited. This means that Sedna is too cold for methane to evaporate from its surface and then fall back as snow, as happens on Triton and probably on Pluto.
Models of internal heating via radioactive decay suggest that Sedna might be capable of supporting a subsurface ocean of liquid water.
Origin
Sedna's exceptionally long and elongated orbit, taking approximately 11,400 years to complete, and distant point of closest approach to the Sun, at 76 AU, have led to much speculation as to its origin.
The Minor Planet Center currently places Sedna in the scattered disc, a group of objects sent into highly elongated orbits by the gravitational influence of Neptune. However, this classification has been contested, as Sedna never comes close enough to Neptune to have been scattered by it, leading some astronomers to conclude that it is in fact the first known member of the inner Oort cloud.
Others speculate that it might have been tugged into its current orbit by a passing star, perhaps one within the Sun's birth cluster, or even that it was captured by the Sun from a passing extrasolar planetary system.
A hypothesis suggests that Sedna's orbit is the result of influence by a large binary companion to the Sun, thousands of AU distant. One such hypothetical companion is Nemesis, a dim companion to the Sun which has been proposed to be responsible for the supposed periodicity of mass extinctions on Earth from cometary impacts, the lunar impact record, and the common orbital elements of a number of long period comets. However, to date no direct evidence of Nemesis has been found, and many lines of evidence (such as crater counts), have thrown its existence into doubt.
Another hypothesis suggests that its orbit may be evidence for an as-yet-undiscovered large planet beyond the orbit of Neptune.
How big is it?
Sedna is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
(225088) 2007 OR10 - 5th Largest TNO? 2nd Largest SDO ?
(225088) 2007 OR10 is a very large trans-Neptunian object. 2007 OR10 is possibly the 5th largest TNO and 2nd largest SDO currently known.
2007 OR10's mass has never been measured, and its diameter is not well known. Some astronomers consider it a dwarf planet and others consider it likely to be one, but it has not been officially classified as a dwarf planet by the IAU.
Discovery
2007 OR10 was discovered by California Institute of Technology astronomers as part of the PhD thesis of Meg Schwamb, who was at the time a graduate student of Michael E. Brown. The survey that found 2007 OR10 was specifically looking for quite distant objects like Sedna.
Naming
The newly discovered TNO was provisionally designated 2007 OR10. Currently, it is the largest body in the Solar System without a name.
Michael E. Brown nicknamed the object "Snow White" for its presumed white color, as it would have to be very large or very bright to be detected by their survey.
Stats
Estimated Diameter: 1420 km (1000 - 1500 km)
Aphelion: 100.79 AU
Perihelion: 33.62 AU
Semi-major axis: 67.21 AU
Orbital Period: 550.98 years
Rotation period: ?
Date discovered: 2007.7.17
Satellite: ?
Classification: TNO, Scattered Disc Object
Orbit
2007 OR10 is on an orbit similar to that of the dwarf planet Eris, making it a scattered disc object.
The preliminary motion of 2007 OR10 librating in a 10:3 resonance with Neptune. This resonance is not confirmed and may be merely a near resonance.
2007 OR10 is currently 86 AU from the Sun. This makes it the 3rd farthest known large body currently known in the Solar System, after Eris (97 AU) and Sedna (88 AU). 2007 OR10 will be further from the Sun than Sedna in 2013 and will be further than both Sedna and Eris by 2045. 2007 OR10 will come to aphelion (furthest distance from the Sun) in 2130.
Physical characteristics
Despite the nickname "Snow White", 2007 OR10 is among the reddest Kuiper belt objects known, comparable only to Quaoar, so the nickname turned out to not be very appropriate. This is probably in part due to methane frosts, which turn red when bombarded by sunlight and cosmic rays.
2007 OR10's spectrum shows signatures for both water ice and methane. The presence of red methane frost on the surfaces of 2007 OR10 implies the existence of a tenuous methane atmosphere, slowly evaporating into space.
Although 2007 OR10 comes closer to the Sun than Quaoar, and is thus warm enough that a methane atmosphere should evaporate, its larger mass makes retention of an atmosphere just possible. The presence of water ice on the surface of 2007 OR10 implies a brief period of cryovolcanism in its distant past.
Dwarf-planet status
If a trans-Neptunian dwarf-planet candidate does not have a known natural satellite with a well determined orbit, astronomers can not directly calculate the objects mass to determine if it might be in hydrostatic equilibrium.
Most objects at that distance are too small and too far away to directly resolve their diameters. Thus candidates' diameters can generally only be estimated from their absolute magnitude and best-fit albedo estimates.
2007 OR10 has no known satellite, so its mass is unknown. The diameter range of 2007 OR10 is based off of an assumed albedo that is a best-fit from Mike Brown's model. It is accepted as a dwarf planet by Mike Brown, and is listed on his website as "nearly certainly" a dwarf planet, saying it "must be a dwarf planet even if predominantly rocky".
2007 OR10's mass has never been measured, and its diameter is not well known. Some astronomers consider it a dwarf planet and others consider it likely to be one, but it has not been officially classified as a dwarf planet by the IAU.
Discovery
2007 OR10 was discovered by California Institute of Technology astronomers as part of the PhD thesis of Meg Schwamb, who was at the time a graduate student of Michael E. Brown. The survey that found 2007 OR10 was specifically looking for quite distant objects like Sedna.
Naming
The newly discovered TNO was provisionally designated 2007 OR10. Currently, it is the largest body in the Solar System without a name.
Michael E. Brown nicknamed the object "Snow White" for its presumed white color, as it would have to be very large or very bright to be detected by their survey.
Stats
Estimated Diameter: 1420 km (1000 - 1500 km)
Aphelion: 100.79 AU
Perihelion: 33.62 AU
Semi-major axis: 67.21 AU
Orbital Period: 550.98 years
Rotation period: ?
Date discovered: 2007.7.17
Satellite: ?
Classification: TNO, Scattered Disc Object
Orbit
2007 OR10 is on an orbit similar to that of the dwarf planet Eris, making it a scattered disc object.
The preliminary motion of 2007 OR10 librating in a 10:3 resonance with Neptune. This resonance is not confirmed and may be merely a near resonance.
2007 OR10 is currently 86 AU from the Sun. This makes it the 3rd farthest known large body currently known in the Solar System, after Eris (97 AU) and Sedna (88 AU). 2007 OR10 will be further from the Sun than Sedna in 2013 and will be further than both Sedna and Eris by 2045. 2007 OR10 will come to aphelion (furthest distance from the Sun) in 2130.
Physical characteristics
Despite the nickname "Snow White", 2007 OR10 is among the reddest Kuiper belt objects known, comparable only to Quaoar, so the nickname turned out to not be very appropriate. This is probably in part due to methane frosts, which turn red when bombarded by sunlight and cosmic rays.
2007 OR10's spectrum shows signatures for both water ice and methane. The presence of red methane frost on the surfaces of 2007 OR10 implies the existence of a tenuous methane atmosphere, slowly evaporating into space.
Although 2007 OR10 comes closer to the Sun than Quaoar, and is thus warm enough that a methane atmosphere should evaporate, its larger mass makes retention of an atmosphere just possible. The presence of water ice on the surface of 2007 OR10 implies a brief period of cryovolcanism in its distant past.
Dwarf-planet status
If a trans-Neptunian dwarf-planet candidate does not have a known natural satellite with a well determined orbit, astronomers can not directly calculate the objects mass to determine if it might be in hydrostatic equilibrium.
Most objects at that distance are too small and too far away to directly resolve their diameters. Thus candidates' diameters can generally only be estimated from their absolute magnitude and best-fit albedo estimates.
2007 OR10 has no known satellite, so its mass is unknown. The diameter range of 2007 OR10 is based off of an assumed albedo that is a best-fit from Mike Brown's model. It is accepted as a dwarf planet by Mike Brown, and is listed on his website as "nearly certainly" a dwarf planet, saying it "must be a dwarf planet even if predominantly rocky".
(136472) Makemake - 4th Largest TNO ? / Largest Cubewano
Makemake is a dwarf planet and perhaps the largest Kuiper belt object (KBO) in the classical population (cubewano) with a diameter that is probably about 2/3 the size of Pluto. Makemake has no known satellite, which makes it unique among the largest KBOs and means that it's mass can only be estimated.
Discovery
Makemake was discovered by the team of Mike Brown, Chad Trujillo and David Rabinowitz on March 31, 2005.
Despite its relative brightness (it is about a fifth as bright as Pluto), Makemake was not discovered until well after many much fainter Kuiper belt objects. Most searches for minor planets are conducted relatively close to the ecliptic (the region of the sky that the Sun, Moon and planets appear to lie in, as seen from Earth), due to the greater likelihood of finding objects there.
Makemake probably escaped detection during the earlier surveys due to its relatively high orbital inclination, and the fact that it was at its farthest distance from the ecliptic at the time of its discovery.
Besides Pluto, Makemake is the only other dwarf planet that was bright enough for Clyde Tombaugh to have possibly detected during his search for trans-Neptunian planets around 1930. At the time of Tombaugh's survey, Makemake was only a few degrees from the ecliptic, near the border of Taurus and Auriga, at an apparent magnitude of 16.0. This position, however, was also very near the Milky Way, and Makemake would have been almost impossible to find against the dense background of stars.
Naming
Makemake was discovered just a few days after Easter and was nicknamed "Easterbunny." by the discovery team. Its official designation was 2005 FY9.
In July 2008, in accordance with IAU rules for classical Kuiper belt objects, 2005 FY9 was given the name of a creator deity. It was decided that, since the planet was discovered on Easter, to name it after Easter Island mythology over Roman Mythology, and thus the name Makemake was chosen.
Makemake, in the Rapa Nui mythology of Easter Island, was the creator of humanity, the god of fertility and the chief god of the "Tangata manu" or bird-man cult (this cult succeeded the island's more famous Moai era).
Stats
Estimated Diameter: 1440 km (1360 – 1480 km)
Aphelion: 53.07 AU
Perihelion: 38.51 AU
Semi-major axis: 45.79 AU
Orbital Period: 309.88 years
Rotation period: 7.77 hrs
Date discovered: 2005.3.31
Satellite: 0
Classification: Dwarf Planet, Kuiper Belt Object - Cubewano
Orbit
Makemake is classified a classical Kuiper belt object (Cubewano), which means its orbit lies far enough from Neptune to remain stable over the age of the Solar System. Cubewanos have perihelia further from the Sun and free from Neptune's perturbation.
Cubewanos have relatively low eccentricities (e below 0.2) and orbit the Sun in much the same way the planets do. Makemake, however, is a member of the "dynamically hot" class of classical KBOs, meaning that it has a high inclination (29°) compared to others in that population.
Makemake is, probably coincidentally, near the 11:6 resonance with Neptune.
Brightness
Makemake is currently visually the second-brightest Kuiper belt object after Pluto, having a March opposition apparent magnitude of 16.7 in the constellation Coma Berenices. This is bright enough to be visible using a high-end amateur telescope.
Size
The size of Makemake is not precisely known, but the detection in infrared by the Spitzer space telescope and Herschel Space Telescope, combined with the similarities of spectrum with Pluto yielded an estimate of the diameter from 1,360 to 1,480 km. This makes Makemake possibly the third largest known trans-Neptunian object after Eris and Pluto.
Makemake is now designated the fourth dwarf planet in the Solar System because it has a bright V-band absolute magnitude of −0.44. This practically guarantees that it is large enough to achieve hydrostatic equilibrium and become an oblate spheroid.
Spectra and surface
Like Pluto, Makemake appears red in the visible spectrum, and significantly redder than the surface of Eris. The near-infrared spectrum is marked by the presence of the broad methane (CH4) absorption bands.
Spectral analysis of Makemake's surface revealed that methane must be present in the form of large grains at least one centimetre in size. In addition large amounts of ethane and tholins may be present as well, most likely created by photolysis of methane by solar radiation. The tholins are probably responsible for the red color of the visible spectrum.
Although evidence exists for the presence of nitrogen ice on its surface, at least mixed with other ices, there is nowhere near the same level of nitrogen as on Pluto and Triton, where it composes more than 98 percent of the crust. The relative lack of nitrogen ice suggests that its supply of nitrogen has somehow been depleted over the age of the Solar System.
The far-infrared (24–70 μm) and submillimeter (70–500 μm) photometry performed by Spitzer and Herschel telescopes revealed that the surface of Makemake is not homogeneous. While the majority of it is covered by nitrogen and methane ices, where the albedo ranges from 78 to 90%, there are small patches of dark terrain whose albedo is only 2 to 12%, and which make up 3–7% of the surface.
Atmosphere
The presence of methane and possibly nitrogen suggests that Makemake could have a transient atmosphere similar to that of Pluto near its perihelion. Nitrogen, if present, will be the dominant component of it.
The existence of an atmosphere also provides a natural explanation for the nitrogen depletion: since the gravity of Makemake is weaker than that of Pluto, Eris and Triton, a large amount of nitrogen was probably lost via atmospheric escape. Methane is lighter than nitrogen, but has significantly lower vapor pressure at temperatures prevalent at the surface of Makemake (30–35 K), which hinders its escape. The result of this process is a higher relative abundance of methane.
How big is it?
Makemake is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the dwarf planet. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Thursday 9 February 2012
(136108) Haumea - 3th Largest TNO?
Haumea is a plutoid, a technical term used to describe dwarf planets beyond Neptune's orbit.
Haumea's extreme elongation makes it unique among known dwarf planets. Although its shape has not been directly observed, calculations from its light curve suggest it is an ellipsoid, with its major axis twice as long as its minor. Nonetheless, its gravity is believed sufficient for it to have relaxed into hydrostatic equilibrium, thereby meeting the definition of a dwarf planet.
This elongation, along with its unusually rapid rotation, high density, and high albedo (from a surface of crystalline water ice), are thought to be the results of a giant collision, which left Haumea the largest member of a collisional family that includes several large trans-Neptunian objects (TNOs) and its two known moons.
Discovery
Two teams claim credit for the discovery of Haumea. Mike Brown and his team at Caltech discovered Haumea in December 28, 2004 on images they had taken on May 6, 2004. On July 20, 2005, they published an online abstract of a report intended to announce the discovery at a conference in September 2005.
At around this time, José Luis Ortiz Moreno and his team at the Instituto de Astrofísica de Andalucía at Sierra Nevada Observatory in Spain found Haumea on images taken on March 7–10, 2003. Ortiz emailed the Minor Planet Center with their discovery on the night of July 27, 2005.
IAU (International Astronomical Union) protocol is that discovery credit for a minor planet goes to whoever first submits a report to the MPC (Minor Planet Center) with enough positional data for a decent determination of its orbit, and that the credited discoverer has priority in choosing a name.
However, the IAU announcement on September 17, 2008, that Haumea had been accepted as a dwarf planet, did not mention a discoverer. The location of discovery was listed as the Sierra Nevada Observatory of the Spanish team, but the chosen name, Haumea, was the Caltech proposal; Ortiz's team had proposed "Ataecina", named for the ancient Iberian goddess of Spring.
Naming
Until it was given a permanent name, the Caltech discovery team used the nickname "Santa" among themselves, as they had discovered Haumea on December 28, 2004, just after Christmas. The Spanish team proposed a separate discovery to the Minor Planet Center (MPC) in July 2005.
On July 29, 2005, Haumea was given its first official label, the temporary designation 2003 EL61, with the "2003" based on the date of the Spanish discovery image. On September 7, 2006, it was numbered and admitted into the official minor planet catalogue as (136108) 2003 EL61.
In September 2006 the Caltech team submitted formal names from Hawaiian mythology to the IAU for both (136108) 2003 EL61 and its moons, in order "to pay homage to the place where the satellites were discovered".
In Hawaiian mythology, Haumea is the Hawaiian goddess of fertility and childbirth. She is the mother of Pele, Kanemilohai, Kā-moho-aliʻi, Nāmakaokaha'i, Kapo and HiʻiakaikapolioPele. She was a powerful being, and gave birth to many creatures, some after turning herself into a young woman to marry her children and grandchildren. She was finally killed by Kaulu.
Stats
Estimated Diameter: 1500 km (1150 - 1500 km)
Aphelion: 51.54 AU
Perihelion: 34.72 AU
Semi-major axis: 43.13 AU
Orbital Period: 283.28 years
Rotation period: 3.92 hrs
Date discovered: 2004.12.28
Satellite: 2
Classification: TNO, KBO - fifth-order 7:12 resonance with Neptune
Orbit
Haumea has a typical orbit for a classical Kuiper-belt object, with an orbital period of about 283 Earth years, a perihelion of 35 AU, and an orbital inclination of 28°.
Haumea's orbit has a slightly greater eccentricity than the other members of its collisional family. This is thought to be due to Haumea's weak fifth-order 7:12 orbital resonance with Neptune gradually modifying its initial orbit over the course of a billion years, through the Kozai effect, which allows the exchange of an orbit's inclination for increased eccentricity.
Haumea displays large fluctuations in brightness over a period of 3.92 hours, which can only be explained by a rotational period of this length. This is faster than any other known equilibrium body in the Solar System, and indeed faster than any other known body larger than 100 km in diameter. This rapid rotation is thought to have been caused by the impact that created its satellites and collisional family.
With a visual magnitude of 17.3, Haumea is the third-brightest object in the Kuiper belt after Pluto and Makemake, and easily observable with a large amateur telescope.
Most early surveys for distant objects focused on the ecliptic - the apparent path that the Sun and planets follows through the sky over the course of the year . As the region of sky close to the ecliptic became well explored, later sky surveys began looking for objects that had been dynamically excited into orbits with higher inclinations, as well as more distant objects, with slower mean motions across the sky. These surveys eventually covered the location of Haumea, with its high orbital inclination and current position far from the ecliptic.
Physical characteristics
The rotation and amplitude of Haumea's light curve place strong constraints on its composition. If Haumea had a low density like Pluto, with a thick mantle of ice over a small rocky core, its rapid rotation would have elongated it to a greater extent than the fluctuations in its brightness allow. Such considerations constrain its density to a range of 2.6–3.3 g/cm3.
This range covers the values for silicate minerals such as olivine and pyroxene, which make up many of the rocky objects in the Solar System. This suggests that the bulk of Haumea is rock covered with a relatively thin layer of ice. A thick ice mantle more typical of Kuiper belt objects may have been blasted off during the impact that formed the Haumean collisional family.
Since no observations of occultations of stars by Haumea or occultations of the dwarf planet with its moons have yet been made, direct, precise measurements of its dimensions, like those that have been made for Pluto, do not yet exist.
Surface
The Gemini and Keck telescopes obtained spectra of Haumea which showed strong crystalline water ice features similar to the surface of Pluto's moon Charon. This is peculiar, because crystalline ice forms at temperatures above 110 K, while the surface temperature of Haumea is below 50 K, a temperature at which amorphous ice is formed.
In addition, the structure of crystalline ice is unstable under the constant rain of cosmic rays and energetic particles from the Sun that strike trans-Neptunian objects. The timescale for the crystalline ice to revert to amorphous ice under this bombardment is on the order of ten million years, while trans-Neptunian objects have been in their present cold-temperature locations for timescales of thousands of millions of years.
Radiation damage should also redden and darken the surface of trans-Neptunian objects where the common surface materials of organic ices and tholin-like compounds are present, as is the case with Pluto. Therefore, the spectra and colour suggest Haumea and its family members have undergone recent resurfacing that produced fresh ice. However, no plausible resurfacing mechanism has been suggested.
Haumea is as bright as snow, with an albedo in the range of 0.6–0.8, consistent with crystalline ice. Other large TNOs such as Eris appear to have albedos as high or higher. Best-fit modeling of the surface spectra suggested that 66% to 80% of the Haumean surface appears to be pure crystalline water ice, with one contributor to the high albedo possibly hydrogen cyanide or phyllosilicate clays. Inorganic cyanide salts such as copper potassium cyanide may also be present.
However, further studies of the visible and near infrared spectra suggest a homomorphous surface covered by an intimate 1:1 mixture of amorphous and crystalline ice, together with no more than 8% organics.
The absence of ammonia hydrate excludes cryovolcanism and the observations confirm that the collisional event must have happened more than 100 million years ago, in agreement with the dynamic studies. The absence of measurable methane in the spectra of Haumea is consistent with a warm collisional history that would have removed such volatiles.
Moons
Two small satellites have been discovered orbiting Haumea, (136108) Haumea I Hiʻiaka and (136108) Haumea II Namaka.
Haumea family
The Haumea family is the only identified trans-Neptunian collisional family; that is, the only group of trans-Neptunian objects (TNOs) with similar orbital parameters and spectra (nearly pure water-ice) that suggest they originated in the disruptive impact of a progenitor body.
Currently, there are 12 confirmed members of the Haumea family.
How big is it?
Haumea is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the dwarf planet. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Wednesday 8 February 2012
(136199) Eris - Largest TNO, Largest dwarf planet ??
Hubble Space Telescope
Eris is the largest object found in orbit around the sun since the discovery of Neptune in 1846. It could be larger than Pluto, discovered in 1930.
Discovery
Eris was discovered by the team of Mike Brown, Chad Trujillo and David Rabinowitz on January 5, 2005, from an ongoing survey of the outer solar system, from images taken on October 21, 2003.
Routine observations were taken by the team on October 21, 2003, using the 1200 mm Samuel Oschin Schmidt telescope at Mount Palomar Observatory. The image of Eris was not discovered at that point due to its very slow motion across the sky: The team's automatic image-searching software excluded all objects moving at less than 1.5 arcseconds per hour to reduce the number of false positives returned.
When Sedna was discovered, it was moving at 1.75 arcsec/h, and in light of that the team reanalyzed their old data with a lower limit on the angular motion, sorting through the previously excluded images by eye. In January 2005, the re-analysis revealed Eris' slow motion against the background stars.
Naming
Due to uncertainty over whether the object would be classified as a planet or a minor planet, Eris was known initially by the provisional designation 2003 UB313, which was granted automatically by the IAU under their naming protocols for minor planets.
As it is the first body discovered that was larger than Pluto, the discovery team used an informal name "Xena" internally ("X" for Planet X).
The informal name was inspired by the eponymous heroine of the television series Xena: Warrior Princess.
The official name was assigned on September 13, 2006. Eris is named after the Greek goddess Eris, a personification of strife and discord.
Stats
Diameter (estimated): 2,330 km (2326 ± 12 km)
Aphelion: 97.56 AU
Perihelion: 37.77 AU
Semi-major axis: 67.67 AU
Orbital Period: 557.8 years
Rotation period: 25.9 ± 8 hrs
Date discovered: 2005.1.5
Satellite: 1
Classification: Dwarf Planet, Scattered Disc Object
Orbit
Eris has an orbital period of 557 years, and as of 2011 lies at 96.6 AU from the Sun, almost its maximum possible distance (its aphelion is 97.56 AU). It came to perihelion between 1698 and 1699, to aphelion around 1977, and will return to perihelion around 2256 to 2258.
Eris and its moon are currently the most distant known objects in the Solar System apart from long-period comets and space probes. However, approximately forty known TNOs, most notably 2006 SQ372, 2000 OO67 and Sedna, while currently closer to the Sun than Eris, have greater average orbital distances than Eris' semimajor axis of 67.7 AU.
The Eridian orbit is highly eccentric, and brings Eris to within 37.9 AU of the Sun, a typical perihelion for scattered objects. This is within the orbit of Pluto, but still safe from direct interaction with Neptune (29.8–30.4 AU).
Unlike the eight planets, whose orbits all lie roughly in the same plane as the Earth's, Eris' orbit is highly inclined: It is tilted at an angle of about 44 degrees to the ecliptic. In about 800 years, Eris will be closer to the Sun than Pluto for some time.
Surface and atmosphere
No surface details of Eris can be resolved from Earth or its orbit with any instrument currently available.
The discovery team followed up their initial identification of Eris with spectroscopic observations made at the 8 m Gemini North Telescope in Hawaii on January 25, 2005. Infrared light from Eris revealed the presence of methane ice, indicating that the surface may be similar to that of Pluto and of Neptune's moon Triton, which also has methane on its surface.
Unlike the somewhat reddish Pluto and Triton, Eris appears almost grey. Pluto's reddish colour is believed to be due to deposits of tholins on its surface, and where these deposits darken the surface, the lower albedo leads to higher temperatures and the evaporation of methane deposits.
In contrast, Eris is far enough away from the Sun that methane can condense onto its surface even where the albedo is low. The condensation of methane uniformly over the surface reduces any albedo contrasts and would cover up any deposits of red tholins.
Even though Eris can be up to three times further from the Sun than Pluto, it approaches close enough that some of the ices on the surface might warm enough to sublime. As methane is highly volatile, its presence shows either that Eris has always resided in the distant reaches of the Solar System where it is cold enough for methane ice to persist, or that the celestial body has an internal source of methane to replenish gas that escapes from its atmosphere.
How big is it?
Eris is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the dwarf planet. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.
Results from the star occultation in October 2011, Eris is estimated to have a diameter of 2,326 +/-12 km, which would make it essentially about the same size as Pluto. Pluto’s diameter is harder to measure because the presence of an atmosphere makes its edge impossible to detect directly by occultations.
Given the error bars in the different size estimates, it is currently uncertain whether Eris or Pluto has the larger diameter. Both Pluto and Eris are estimated to have solid-body diameters of about 2330 km.
Tuesday 7 February 2012
(50000) Quaoar - 7th Largest TNO? 2nd Largest Cubewano
50000 Quaoar is a rocky trans-Neptunian object in the Kuiper belt with one known moon. Several astronomers consider it to be a dwarf planet, although the IAU has not formally designated it as such yet.
Discovery
Quaoar was discovered on June 4, 2002 by astronomers Chad Trujillo and Michael Brown at the California Institute of Technology, from images acquired at the Samuel Oschin Telescope at Palomar Observatory.
The discovery of this magnitude 18.5 object, located in the constellation Ophiuchus, was announced on October 7, 2002, at a meeting of the American Astronomical Society.
The earliest prediscovery image proved to be a May 25, 1954 plate from Palomar Observatory.
Naming
Prior to IAU approval of the name, Quaoar went by the provisional designation 2002 LM60.
The minor planet number 50000 was not coincidence, but chosen to commemorate a particularly large object found in the search for a Pluto-sized object in the Kuiper belt, parallel to the similarly numbered 20000 Varuna.
However, later even larger discoveries were simply numbered according to the order in which their orbits were confirmed.
Quaoar is named for the Tongva creator god, following International Astronomical Union naming conventions for non-resonant Kuiper belt objects. The Tongva are the native people of the area around Los Angeles, where the discovery of Quaoar was made.
In the mythology of the so-called Mission Indians of coastal Southern California, Chingichngish (also spelled Chinigchinix, Chinigchinich, Changitchnish, etc.) also known as Quaoar (also Qua-o-ar, Kwawar, etc.) and by other names including Ouiamot, Tobet and Saor is the name of an important figure.
Chinigchinix was born, or first appeared, after the death of Wiyot, a tyrannical ruler of the first beings, who was poisoned by his sons. Wiyot's murder brought death into the world, and as a consequence, the male creator Night divided the first human ancestors into distinct peoples, assinging them languages and territories.
Stats
Estimated Diameter: 1170 km
Aphelion: 45.12 AU
Perihelion: 41.70 AU
Semi-major axis: 43.41 AU
Orbital Period: 285.97 years
Rotation period: 17.68 hrs
Date discovered: 2002.6.4
Satellite: 1
Classification: TNO, KBO - Cubewano
Star Occultation
On 2011-05-04 Quaoar occulted a 16th-magnitude star, which gave 1170 km as the longest chord and suggests an elongated shape.
Orbit
Quaoar orbits at about 43 astronomical units from the Sun with an orbital period of 286 years. Quaoar's orbit is near-circular and moderately-inclined at approximately 8°, and is not significantly perturbed by Neptune, unlike Pluto which is in 2:3 orbital resonance with Neptune.
Quaoar is the second largest body that is classified as a cubewano.
Physical characteristics
With a density estimated to be around 4.2 ± 1.3 g/cm3, Quaoar is believed to be a mixture of mostly rock with some ice and is possibly the densest known object in the Kuiper belt. Even dwarf planet Haumea is only estimated to have a density of 2.6 g/cm3.
Planetary scientist Erik Asphaug has suggested that Quaoar may have collided with a small planet up to the size of Mars, stripping the lower-density mantle from Quaoar, and leaving behind the denser core. He envisions that Quaoar was originally covered by a mantle of ice that made it 300 to 500 kilometers bigger than it is today, and that it collided with another Kuiper-belt body about twice its size — an object roughly the diameter of Pluto, possibly Pluto itself.
As of 2008, Quaoar is currently only 14 AU from Pluto making it the closest large body to the Pluto–Charon system. By Kuiper Belt standards this is very close.
Cryovolcanism
In 2004, scientists were surprised to find signs of crystalline ice on Quaoar, indicating that the temperature rose to at least −160 °C sometime in the last ten million years.
Speculation began as to what could have caused Quaoar to heat up from its natural temperature of −220 °C. Some have theorized that a barrage of mini-meteors may have raised the temperature, but the most discussed theory speculates that cryovolcanism may be occurring, spurred by the decay of radioactive elements within Quaoar's core.
More precise (2007) observations of Quaoar's near infrared spectrum indicate the presence of small quantity (5%) of (solid) methane and ethane. Given its boiling point (112 K), methane is a volatile ice at average Quaoar surface temperatures, unlike water ice or ethane (boiling point 185 K).
Both models and observations suggest that only a few larger bodies (Pluto, Eris, Makemake) can retain the volatile ices while the dominant population of small TNOs lost them. Quaoar, with only small amounts of methane, appears to be in an intermediary category.
Moon
Quaoar has one known satellite, Weywot.
Discovery
Quaoar was discovered on June 4, 2002 by astronomers Chad Trujillo and Michael Brown at the California Institute of Technology, from images acquired at the Samuel Oschin Telescope at Palomar Observatory.
The discovery of this magnitude 18.5 object, located in the constellation Ophiuchus, was announced on October 7, 2002, at a meeting of the American Astronomical Society.
The earliest prediscovery image proved to be a May 25, 1954 plate from Palomar Observatory.
Naming
Prior to IAU approval of the name, Quaoar went by the provisional designation 2002 LM60.
The minor planet number 50000 was not coincidence, but chosen to commemorate a particularly large object found in the search for a Pluto-sized object in the Kuiper belt, parallel to the similarly numbered 20000 Varuna.
However, later even larger discoveries were simply numbered according to the order in which their orbits were confirmed.
Quaoar is named for the Tongva creator god, following International Astronomical Union naming conventions for non-resonant Kuiper belt objects. The Tongva are the native people of the area around Los Angeles, where the discovery of Quaoar was made.
In the mythology of the so-called Mission Indians of coastal Southern California, Chingichngish (also spelled Chinigchinix, Chinigchinich, Changitchnish, etc.) also known as Quaoar (also Qua-o-ar, Kwawar, etc.) and by other names including Ouiamot, Tobet and Saor is the name of an important figure.
Chinigchinix was born, or first appeared, after the death of Wiyot, a tyrannical ruler of the first beings, who was poisoned by his sons. Wiyot's murder brought death into the world, and as a consequence, the male creator Night divided the first human ancestors into distinct peoples, assinging them languages and territories.
Stats
Estimated Diameter: 1170 km
Aphelion: 45.12 AU
Perihelion: 41.70 AU
Semi-major axis: 43.41 AU
Orbital Period: 285.97 years
Rotation period: 17.68 hrs
Date discovered: 2002.6.4
Satellite: 1
Classification: TNO, KBO - Cubewano
Star Occultation
On 2011-05-04 Quaoar occulted a 16th-magnitude star, which gave 1170 km as the longest chord and suggests an elongated shape.
Orbit
Quaoar orbits at about 43 astronomical units from the Sun with an orbital period of 286 years. Quaoar's orbit is near-circular and moderately-inclined at approximately 8°, and is not significantly perturbed by Neptune, unlike Pluto which is in 2:3 orbital resonance with Neptune.
Quaoar is the second largest body that is classified as a cubewano.
Physical characteristics
With a density estimated to be around 4.2 ± 1.3 g/cm3, Quaoar is believed to be a mixture of mostly rock with some ice and is possibly the densest known object in the Kuiper belt. Even dwarf planet Haumea is only estimated to have a density of 2.6 g/cm3.
Planetary scientist Erik Asphaug has suggested that Quaoar may have collided with a small planet up to the size of Mars, stripping the lower-density mantle from Quaoar, and leaving behind the denser core. He envisions that Quaoar was originally covered by a mantle of ice that made it 300 to 500 kilometers bigger than it is today, and that it collided with another Kuiper-belt body about twice its size — an object roughly the diameter of Pluto, possibly Pluto itself.
As of 2008, Quaoar is currently only 14 AU from Pluto making it the closest large body to the Pluto–Charon system. By Kuiper Belt standards this is very close.
Cryovolcanism
In 2004, scientists were surprised to find signs of crystalline ice on Quaoar, indicating that the temperature rose to at least −160 °C sometime in the last ten million years.
Speculation began as to what could have caused Quaoar to heat up from its natural temperature of −220 °C. Some have theorized that a barrage of mini-meteors may have raised the temperature, but the most discussed theory speculates that cryovolcanism may be occurring, spurred by the decay of radioactive elements within Quaoar's core.
More precise (2007) observations of Quaoar's near infrared spectrum indicate the presence of small quantity (5%) of (solid) methane and ethane. Given its boiling point (112 K), methane is a volatile ice at average Quaoar surface temperatures, unlike water ice or ethane (boiling point 185 K).
Both models and observations suggest that only a few larger bodies (Pluto, Eris, Makemake) can retain the volatile ices while the dominant population of small TNOs lost them. Quaoar, with only small amounts of methane, appears to be in an intermediary category.
Moon
Quaoar has one known satellite, Weywot.
Saturday 4 February 2012
10th Largest Moon of Neptune - Neso (13th Moon outwards from Neptune)
Neso, is the outermost irregular retrograde natural satellite of Neptune.
Neso is the 10th overall largest satellite of Neptune and 62th largest moon in the Solar System currently known.
Discovery
Matthew J. Holman, Harvard-Smithsonian Center for Astrophysics (CfA); John J. Kavelaars, National Research Council of Canada; T. Grav, University of Oslo and CfA; and W. Fraser and Dan Milisavljevic, McMaster University, reported the discovery of three satellites of Neptune on CCD images obtained in 14 August 2002 with the 4-m Blanco telescope at Cerro Tololo.
Naming
The moon was given the temporary designation S/2002 N4.
Neso the moon is named after one of the Nereids, the fifty daughters of Nereus and Doris.
Stats
Diameter (mean): 60 km
Semi-major axis: 49,285,000 km
Orbital Period: -9740.73 days
Rotation Period: ?
Orbit
Neso orbits Neptune at a distance of more than 48 Gm (million km), making it the most distant known moon of any planet. It follows a highly inclined and highly eccentric orbit.
Formation
Given the similarity of the orbit's parameters with the next inner satellite, Psamathe, it was suggested that both irregular satellites could have a common origin in the break-up of a larger moon.
Physical characteristics
Little is known about Neso.
Neso is about 60 kilometers in diameter (assuming an albedo of 0.04).
Neso is the 10th overall largest satellite of Neptune and 62th largest moon in the Solar System currently known.
Discovery
Matthew J. Holman, Harvard-Smithsonian Center for Astrophysics (CfA); John J. Kavelaars, National Research Council of Canada; T. Grav, University of Oslo and CfA; and W. Fraser and Dan Milisavljevic, McMaster University, reported the discovery of three satellites of Neptune on CCD images obtained in 14 August 2002 with the 4-m Blanco telescope at Cerro Tololo.
Naming
The moon was given the temporary designation S/2002 N4.
Neso the moon is named after one of the Nereids, the fifty daughters of Nereus and Doris.
Stats
Diameter (mean): 60 km
Semi-major axis: 49,285,000 km
Orbital Period: -9740.73 days
Rotation Period: ?
Orbit
Neso orbits Neptune at a distance of more than 48 Gm (million km), making it the most distant known moon of any planet. It follows a highly inclined and highly eccentric orbit.
Formation
Given the similarity of the orbit's parameters with the next inner satellite, Psamathe, it was suggested that both irregular satellites could have a common origin in the break-up of a larger moon.
Physical characteristics
Little is known about Neso.
Neso is about 60 kilometers in diameter (assuming an albedo of 0.04).
Friday 3 February 2012
10th Largest Moon of Uranus - Belinda (10th Moon outwards from Uranus)
Belinda is an inner satellite of the planet Uranus.
Belinda is the 10th largest Moon of Uranus and the 53th largest moon in the Solar System currently known.
Discovery
Belinda was discovered by Stephen P. Synnott, who is an American astronomer and Voyager scientist, from the images taken by Voyager 2 on 13 January 1986.
Naming
The moon was given the temporary designation S/1986 U5.
Belinda the moon is named after Belinda, the heroine of Alexander Pope's The Rape of the Lock. Belinda was a beautiful young lady with wondrous hair, two locks of which hang gracefully in curls.
Alexander Pope based The Rape of the Lock on an actual incident in which a British nobleman, Lord Petre, cut off a lock of hair dangling tantalizingly from the head of the beautiful Arabella Fermor. Petre’s daring theft of the lock set off a battle royal between the Petre and Fermor families. John Caryll – a friend of Pope and of the warring families–persuaded the great writer to pen a literary work satirizing the absurdity and silliness of the dispute. The result was one of the greatest satirical poems in all of literature.
Stats
Diameter (mean): 80 km
Semi-major axis: 75,255 km
Orbital Period: 0.623 days
Orbit
Belinda takes as long to rotate on its axis as it does to make one orbit of Uranus; and therefore always keeps the same hemisphere pointed to Uranus.
Belinda belongs to a group of satellites called the Portia Group, which includes Portia, Bianca, Cressida, Desdemona, Rosalind, Cupid, Juliet and Perdita. These satellites have similar orbits and photometric properties.
Physical characteristics
Little is known about Belinda beyond its size of about 80 km, orbit and geometric albedo of about 0.08.
The Voyager 2 images show Belinda as an elongated object with its major axis pointing towards Uranus. The moon is very elongated, with its short axis 0.5 ± 0.1 times the long axis. Belinda's surface is grey in color.
Exploration Status
No close-up image of Belinda has been photographed.
No mission is planned in the foreseeable future.
Belinda is the 10th largest Moon of Uranus and the 53th largest moon in the Solar System currently known.
Discovery
Belinda was discovered by Stephen P. Synnott, who is an American astronomer and Voyager scientist, from the images taken by Voyager 2 on 13 January 1986.
Naming
The moon was given the temporary designation S/1986 U5.
Belinda the moon is named after Belinda, the heroine of Alexander Pope's The Rape of the Lock. Belinda was a beautiful young lady with wondrous hair, two locks of which hang gracefully in curls.
Alexander Pope based The Rape of the Lock on an actual incident in which a British nobleman, Lord Petre, cut off a lock of hair dangling tantalizingly from the head of the beautiful Arabella Fermor. Petre’s daring theft of the lock set off a battle royal between the Petre and Fermor families. John Caryll – a friend of Pope and of the warring families–persuaded the great writer to pen a literary work satirizing the absurdity and silliness of the dispute. The result was one of the greatest satirical poems in all of literature.
Stats
Diameter (mean): 80 km
Semi-major axis: 75,255 km
Orbital Period: 0.623 days
Orbit
Belinda takes as long to rotate on its axis as it does to make one orbit of Uranus; and therefore always keeps the same hemisphere pointed to Uranus.
Belinda belongs to a group of satellites called the Portia Group, which includes Portia, Bianca, Cressida, Desdemona, Rosalind, Cupid, Juliet and Perdita. These satellites have similar orbits and photometric properties.
Physical characteristics
Little is known about Belinda beyond its size of about 80 km, orbit and geometric albedo of about 0.08.
The Voyager 2 images show Belinda as an elongated object with its major axis pointing towards Uranus. The moon is very elongated, with its short axis 0.5 ± 0.1 times the long axis. Belinda's surface is grey in color.
Exploration Status
No close-up image of Belinda has been photographed.
No mission is planned in the foreseeable future.
Thursday 2 February 2012
10th Largest Moon of Saturn - Janus (6th Moon outwards from Saturn)
Janus is an inner moon of Saturn and it is co-orbital with another moon Epimetheus.
Janus is the 10th largest moon of Saturn, and the 30th largest moon in the Solar System currently known.
Discovery
Janus occupies practically the same orbit as the moon Epimetheus. This caused some confusion for astronomers, who assumed that there was only one body in that orbit, and for a long time struggled to figure out what was going on. It was eventually realized that they were trying to reconcile observations of two distinct objects as a single object.
The discovery of Janus is attributed to its first observer: Audouin Charles Dollfus, on December 15, 1966. Previously, Jean Texereau had photographed Janus on October 29, 1966 without realising it. Dollfus named it at the same occasion.
On December 18, Richard Walker made a similar observation which is now credited as the discovery of Epimetheus.
Twelve years later, in October 1978, Stephen M. Larson and John W. Fountain realised that the 1966 observations were best explained by two distinct objects (Janus and Epimetheus) sharing very similar orbits. Voyager 1 confirmed this in 1980.
Naming
The moon was given the temporary designation S/1966 S2 after discovery.
Due to uncertainty in Janus's orbital status, the moon was observed on subsequent occasions and given different provisional designations. It was observed by the Pioneer 11 probe when it passed near Saturn on September 1, 1979: three energetic particle detectors observed its "shadow" (S/1979 S2). Janus was observed by Dan Pascu on February 19, 1980 (S/1980 S1) and then by John W. Fountain, Stephen M. Larson, Harold J. Reitsema and Bradford A. Smith on the 23rd (S/1980 S2).
Janus the moon is named after Janus, the two-faced Roman god.
In ancient Roman religion and mythology, Janus is the god of beginnings and transitions, thence also of gates, doors, doorways, endings and time. He is usually a two-faced god since he looks to the future and the past.
Although the name was informally proposed soon after the initial 1966 discovery, Janus was not officially given this name until 1983.
Stats
Diameter (mean): 179 km
Semi-major axis: 151,472 km
Orbital Period: 0.695 days
Co-orbital moons
Janus and Epimetheus share their orbits, the difference in semi-major axes being less than either's mean diameter. This means the moon with the smaller semi-major axis will slowly catch up with the other. As it does this, the moons gravitationally tug at each other, increasing the semi-major axis of the moon that has caught up and decreasing that of the other.
This reverses their relative positions (proportionally to their masses) and causes this process to begin anew with the moons' roles reversed. In other words, they effectively swap orbits, ultimately oscillating both about their mass-weighted mean orbit.
Janus rotates synchronously with its orbital period, keeping one face pointed toward Saturn.
Formation
Janus and Epimetheus may have formed from a disruption of a single parent to form co-orbital satellites, but if this is the case the disruption must have happened early in the history of the satellite system.
Physical characteristics
Janus is extensively cratered with several craters larger than 30 km but few linear features. Janus's surface appears to be older than Prometheus' but younger than Pandora's. From its very low density and relatively high albedo, it seems likely that Janus is a very porous and icy rubble pile. The moon is also highly non-spherical.
Ring
A faint dust ring is present around the region occupied by the orbits of Janus and Epimetheus, as revealed by images taken in forward-scattered light by the Cassini spacecraft in 2006.
The ring has a radial extent of about 5000 km. Its source is particles blasted off the moons' surfaces by meteoroid impacts, which then form a diffuse ring around their orbital paths.
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