13th Largest Moon of Saturn - Pandora (5th Moon outwards from Saturn)

Pandora is an inner satellite of Saturn.

Pandora is the 13th largest moon of Saturn, and the 52th largest moon in the Solar System currently known.

Discovery

Pandora was discovered in October 1980 from photos taken by the Voyager 1 probe.


Naming

Pandora was provisionally designated S/1980 S26. In late 1985, the moon was officially named after Pandora, from Greek mythology.

In Greek mythology, Pandora was allegedly the first woman, who was made out of clay. As Hesiod related it, each god helped create her by giving her unique gifts. Zeus ordered Hephaestus to mold her out of earth as part of the punishment of mankind for Prometheus' theft of the secret of fire, and all the gods joined in offering her "seductive gifts".

Pandora's Box is an artifact in Greek mythology, taken from the myth of Pandora's creation in Hesiod's Works and Days. The "box" was actually a large jar given to Pandora, which contained all the evils of the world, although the particular evils, aside from plagues and diseases, are not specified in detail by Hesiod. When Pandora opened the jar, all its contents except for one item were released into the world. The one remaining item was Hope. Today, to open Pandora's box means to create evil that cannot be undone.

Stats

Diameter (mean): 81.4 ± 3.0 km

Semi-major axis: 141,720 km

Orbital Period: 0.629 days

Orbit

Pandora rotates synchronously with its orbital period, keeping one face pointed toward Saturn.

Pandora is the outer shepherd satellite of the F Ring.

The orbit of Pandora appears to be chaotic, as a consequence of a series of four 118:121 mean motion resonances with Prometheus. The most appreciable changes in their orbits occur approximately every 6.2 years, when the periapsis of Pandora lines up with the apoapsis of Prometheus and the moons approach to within about 1,400 kilometres.

Pandora also has a 3:2 mean-motion resonance with Mimas.

Physical Characteristics

Pandora is more heavily cratered than nearby Prometheus, and has at least two large craters 30 kilometres in diameter.

From Pandora's very low density and relatively high albedo, it seems likely that it is a very porous icy body. There is a lot of uncertainty in these values, however, so this remains to be confirmed.

13th Largest Moon of Jupiter - Lysithea (12th Moon outwards from Jupiter)

Lysithea is a prograde irregular satellite of Jupiter.

Lysithea is the 13th largest moon of Jupiter and 75th largest moon in the Solar System currently known.

Discovery

Lysithea was discovered by Seth Barnes Nicholson on July 6, 1938 with the 100-inch (2.5 m) Hooker telescope at the Mount Wilson Observatory.

Naming

Lysithea the moon is named after the mythological Lysithea, daughter of Oceanus and one of Zeus' lovers.

In Greek mythology, Lysithea was a daughter of Oceanus and one of Zeus' lovers.

Lysithea didn't receive its present name until 1975; before then, it was simply known as Jupiter X. Or it was sometimes called "Demeter" from 1955 to 1975.

In Greek mythology, Demeter is the goddess of the harvest, who presided over grains and the fertility of the earth.

A name ending in "a" was chosen for this moon in keeping with the International Astronomical Union's policy for designating Jupiter's outer moons which have prograde orbits (orbiting in the same direction as Jupiter's rotation).

Stats

Diameter (mean): 36 km

Semi-major axis: 11,740,560 km

Orbital Period: 259.2 day

Orbit

Lysithea belongs to the Himalia group, a family of Jovian satellites which have similar orbits and appearance, and are therefore thought to have a common origin. Its orbital elements are as of January 2000. They are continuously changing due to solar and planetary perturbations.

Physical characteristics

Lysithea has an estimated diameter of 36 km (assuming an albedo of 0.04).

Lysithea may be a chunk of an asteroid (a C- or D-class asteroid, judging by the fact that it reflects only about 4% of the light it receives), which was broken apart in a collision either before or after being captured by Jupiter's gravity.

In this scenario, the other pieces became the other moons in the Himalia group: Leda, Himalia (the largest) and Elara. A fifth moon, called S/2000 J11, only about 2 km in radius, was considered a candidate for this group. However, it was lost before its orbit could be definitively determined.

S/2000 J11 may have crashed into Himalia, reuniting two pieces of the former asteroid, and perhaps creating a faint temporary ring of Jupiter near the orbit of Himalia.

Centaurs (minor planets)

Centaurs are an unstable orbital class of minor planets that behave with characteristics of both asteroids and comets.

The generic definition of a centaur is a small body that orbits the Sun between Jupiter and Neptune and crosses the orbits of one or more of the giant planets.

It has been estimated that there are around 44,000 centaurs in the Solar System with diameters larger than 1 km.

Naming

They are named after the mythological race of beings, centaurs, which were a mixture of horse and human.

In Greek mythology, a centaur or hippocentaur is a member of a composite race of creatures, part human and part horse. In early Attic and Boeotian vase-paintings, they are depicted with the hindquarters of a horse attached to human; in later renderings centaurs are given the torso of a human joined at the waist to the horse's withers, where the horse's neck would be.

The centaurs were usually said to have been born of Ixion and Nephele (the cloud made in the image of Hera).

Orbits

Centaurs' orbits are characterised by a wide range of eccentricity, from highly eccentric (Pholus, Asbolus, Amicus, Nessus) to more circular (Chariklo and the Saturn-crossers: Thereus, Okyrhoe).

Since the centaurs cross the orbits of the giant planets and are not protected by orbital resonances, their orbits are unstable within a timescale of 10⁶ – 10⁷ years.

Dynamical studies of their orbits indicate that centaurs are probably an intermediate orbital state of objects transitioning from the Kuiper belt to the Jupiter family of short-period comets. Objects may be perturbed from the Kuiper belt, whereupon they become Neptune-crossing and interact gravitationally with that planet. They then become classed as centaurs, but their orbits are chaotic, evolving relatively rapidly as the centaur makes repeated close approaches to one or more of the outer planets.

Some centaurs will evolve into Jupiter-crossing orbits whereupon their perihelia may become reduced into the inner Solar System and they may be reclassified as active comets in the Jupiter family if they display cometary activity. Any centaur that is perturbed close enough to the Sun is expected to become a comet.

Centaurs will thus ultimately collide with the Sun or a planet or else they may be ejected into interstellar space after a close approach to one of the planets, particularly Jupiter.

Physical characteristics

The relatively small size of centaurs precludes surface observations, but colour indices and spectra can indicate possible surface composition and can provide insight into the origin of the bodies.

Color

Centaurs display a puzzling diversity of colour that challenges any simple model of surface composition.

Centaurs appear to be grouped into two classes:
1. Very red, for example 5145 Pholus
2. Blue (or blue-grey), for example 2060 Chiron

There are numerous theories to explain this colour difference, but they can be divided broadly into two categories:
1. The colour difference results from a difference in the origin and/or composition of the centaur.
2. The colour difference reflects a different level of space-weathering from radiation and/or cometary activity.

Spectra

The interpretation of spectra is often ambiguous, related to particle sizes and other factors. For example, if there is cometary activity, the spectra observed vary depending on the period of the observation. Water ice signature was detected during a period of low activity and disappeared during high activity.

Origin

The study of centaur development is rich in recent developments but still hampered by limited physical data. Different models have been put forward for possible origin of centaurs.

Simulations indicate that the orbit of some Kuiper-belt objects can be perturbed, resulting in the object's expulsion so that it becomes a centaur. Scattered disk objects would be dynamically the best candidates for such expulsions, but their colours do not fit the bicoloured nature of the centaurs. Plutinos are a class of Kuiper-belt object that display a similar bicoloured nature, and there are suggestions that not all plutinos' orbits are as stable as initially thought, due to perturbation by Pluto.

Further developments are expected with more physical data on KBOs.

34th Largest Asteroid, 6 Hebe

6 Hebe is a large main-belt asteroid and the 34th largest asteroid currently known.




Discovery

Hebe was the sixth asteroid to be discovered, on July 1, 1847 by Karl Ludwig Hencke at Driesen. It was the second and final asteroid discovery by Hencke, who had previously found 5 Astraea.

Naming

The name Hebe, goddess of youth, was proposed by Carl Friedrich Gauss, who was a German mathematician and physical scientist who contributed significantly to many fields, including number theory, statistics, analysis, differential geometry, geodesy, geophysics, electrostatics, astronomy and optics.

In Greek mythology, Hēbē is the goddess of youth (Roman equivalent: Juventas). She is the daughter of Zeus and Hera. Hebe was the cupbearer for the gods and goddesses of Mount Olympus, serving their nectar and ambrosia, until she was married to Heracles.

The name Hebe comes from Greek word meaning "youth" or "prime of life". Juventas likewise means "youth", as can be seen in such derivatives as juvenile. In art, Hebe is usually depicted wearing a sleeveless dress. Hebe was also worshipped as a goddess of pardons or forgiveness; freed prisoners would hang their chains in the sacred grove of her sanctuary at Phlius.

Stats

Diameter (mean): 185 km
Aphelion: 2.914 AU
Perihelion: 1.935 AU
Semi-major axis: 2.425 AU
Orbital Period: 3.78 years
Rotation period: 7.27 hrs
Date discovered: 1847.7.1
Class: S
Type: Main-belt Asteroid
Satellite: 1 ?
(data from JPL Small-Body Database)

Orbit and Brightness

In brightness, Hebe is the fifth brightest object in the asteroid belt after Vesta, Ceres, Iris and Pallas. It has a mean opposition magnitude of +8.3, about equal to the mean brightness of Titan and can reach +7.5 at an opposition near perihelion.

Physical characteristics

Hebe containing around half a percent of the mass of the asteroid belt. Hebe's size/volume does not rank among the top twenty asteroids. But its apparently high bulk density is even greater than that of the Earth's Moon or even Mars. This high bulk density suggests an extremely solid body that has not been impacted by collisions, which is not typical of asteroids of its size, as they tend to be loosely bound rubble piles.

Lightcurve analysis suggests that Hebe has a rather angular shape, which may be due to several large impact craters. Hebe rotates in a prograde direction.

Major meteorite source

6 Hebe is the probable parent body of the H chondrite meteorites and the IIE iron meteorites. Remarkably, this would imply that it is the source of about 40% of all meteorites striking Earth. Evidence for this connection includes:

- The spectrum of Hebe matches a mix of 60% H chondrite and 40% IIE iron meteorite material.

- The IIE type are unusual among the iron meteorites, and probably formed from impact melt, rather than being fragments of the core of a differentiated asteroid.

- The IIE irons and H chondrites likely come from the same parent body, due to similar trace mineral and oxygen isotope ratios.

- Asteroids with spectra similar to the ordinary chondrite meteorites (accounting for 85% of all falls, including the H chondrites) are extremely rare.

- 6 Hebe is extremely well placed to send impact debris to Earth-crossing orbits. Ejecta with even relatively small velocities (~280 m/s) can enter the chaotic regions of the 3:1 Kirkwood gap at 2.50 AU and the nearby secular resonance which determines the high-inclination edge of the asteroid belt at about 16° inclinations hereabouts.

- Of the asteroids in this "well-placed" orbit, Hebe is the largest.

- An analysis of likely contributors to the Earth's meteorite flux places 6 Hebe at the top of the list, due to its position and relatively large size. If Hebe is not the H-chondrite parent body, then where are the meteorites from Hebe?

Satellite

On March 5, 1977 Hebe occulted Kaffaljidhma (γ Ceti), a moderately bright 3rd magnitude star. No other observed occultations by Hebe have been reported.

As a result of that occultation, a small Hebean moon was reported by Paul D. Maley. It was nicknamed "Jebe". However, the discovery has not been confirmed.

33th Largest Asteroid, 16 Psyche

16 Psyche is a large main-belt asteroids and the largest member of the Themistian asteroid family. Psyche is the 33th largest asteroid and is the most massive metallic M-type asteroid currently known.

Discovery

16 Psyche was discovered on 17 March 1852 by Annibale de Gasparis at Naples.

Naming

Psyche the asteroid was named after the Greek mythological figure Psyche.

In Greek mythology, Psyche was the deification of the human soul. She was portrayed in ancient mosaics as a goddess with butterfly wings (because psyche is also the Greek word for 'butterfly').

Psyche was originally the youngest daughter of the king and queen of Sicily, and the most beautiful person on the island. Suitors flocked to ask for her hand.

She eventually boasted that she was more beautiful than Aphrodite (Venus) herself, and Aphrodite sent Eros to transfix her with an arrow of desire, to make her fall in love with the nearest person or thing available. But even Eros (Cupid) fell in love with her, and took her to a secret place, eventually marrying her and having her made a goddess by Zeus (Jupiter).

Stats

Diameter (mean): 186 km
Aphelion: 3.328 AU
Perihelion: 2.521 AU
Semi-major axis: 2.922 AU
Orbital Period: 4.99 years
Rotation period: 4.20 hrs
Date discovered: 1852.3.17
Class: M
Type: Main-belt Asteroid

Physical Characteristics

Radar observations indicate Pysche has a fairly pure iron–nickel composition. Psyche appears to be a genuine case of an exposed metallic core from a larger differentiated parent body. Psyche is the most massive metallic M-type asteroid currently known.

Unlike some other M-type asteroids, Psyche shows no sign of the presence of water or water-bearing minerals on its surface, consistent with its interpretation as a metallic body. Small amounts of pyroxene appear to be present.

It is possible that at least some examples of enstatite chondrite meteorites originated from this asteroid, based on similar spectral analysis results.

Asteroid family ?

If Psyche is the core remnant of a larger parent body, we might expect other asteroids on similar orbits. However, we do not find any asteroid family belonging to Psyche.

One hypothesis is that the collision occurred very early in the Solar System's history, and all the other remnants have since been ground into fragments by subsequent collisions or had their orbits perturbed beyond recognition.

Star occultation

16 Psyche on August 21, 2010 occulted the star HIP 22112 in Taurus over a long path that passed from the central Baja peninsula to the central Atlantic coast. Maximum duration was predicted to be 10.3 seconds. For this event, 12 observers at 17 sites recorded 14 chords across the profile of the asteroid. Fifteen sites used video to record the event while one station used visual techniques and one station used drift scan.

The resulting chords and least squares ellipse produce a smooth ellipse with dimensions of 235.4 ± 3.9 x 230.4 ± 2.4 km. The maximum occultation duration of 10.12 seconds occurred at station nine and is just 2% shorter than predicted. The observed path was just 32 km north of the prediction.

Only two other occultations by Psyche have been observed: a single-chord event on 2002 March 22 and a five-chord occultation on 2004 May 16 (TYC 5783-01228-1). The four useable chords for the 2004 event were spaced well across the asteroid, being fit by an ellipse with axes of 214 ± 6 km by 181 ± 7 km.

32th Largest Asteroid, 128 Nemesis

128 Nemesis is a large asteroid in the main asteroid belt. It is the 32th largest asteroid currently known.

Discovery

Nemesis was discovered by James Craig Watson on November 25, 1872 from Ann Arbor, Michigan, USA.

Naming

Nemesis the asteroid was named after Nemesis, the goddess of retribution in Greek mythology.

In Greek mythology, Nemesis, also called Rhamnousia/Rhamnusia ("the goddess of Rhamnous") at her sanctuary at Rhamnous, north of Marathon, was the spirit of divine retribution against those who succumb to hubris (arrogance before the gods). The Greeks personified vengeful fate as a remorseless goddess: the goddess of revenge.

Stats

Diameter (mean): 188 km
Aphelion: 3.099 AU
Perihelion: 2.408 AU
Semi-major axis: 2.751 AU
Orbital Period: 4.56 years
Rotation period: 39 hrs
Date discovered: 1872.11.25
Class: C
Group: Nemesis group
Type: Main-belt Asteroid
Satellite: 0
(data from JPL Small-Body Database)

Orbit

Nemesis is the largest member of the Nemesian asteroid family bearing its name.

Physical Characteristics

Nemesis is a very dark main-belt asteroid, of carbonaceous composition.

Rotation

Nemesis rotates very slowly, taking about one and half Earth days (39 hours) to complete one revolution.

Extensive photoelectric lightcurves of Nemesis show that it has extremely long rotational period, the longest known currently for asteroids.

31th Largest Asteroid, 372 Palma

372 Palma is a large asteroid in the main asteroid belt. It is the 31th largest asteroid currently known.

Discovery

Palma was discovered by Auguste Honoré Charlois on August 19, 1893 from Nice.

Naming

Palma the asteroid is named for the capital city of Majorca, an island located in the Mediterranean Sea, one of the Balearic Islands (Spain), and south of France.

The capital of Majorca, Palma, was founded as a Roman camp called Palmaria upon the remains of a Talaiotic settlement. The turbulent history of the city saw it subject to several Vandal sackings during the fall of the Roman Empire. It was later reconquered by the Byzantines, colonised by the Moors (who called it Medina Mayurqa), and finally established by James I of Aragon. In 1983, Palma became the capital of the autonomous region of the Balearic Islands.

Palma the asteroid is one of seven of Charlois's discoveries that was expressly named by the Astromomisches Rechen-Institut (Astronomical Calculation Institute).

Stats

Diameter (mean): 189 km
Aphelion: 3.971 AU
Perihelion: 2.327 AU
Semi-major axis: 3.149 AU
Orbital Period: 5.59 years
Rotation period: 8.57 hrs
Date discovered: 1893.8.19
Class: B
Type: Main-belt Asteroid
(data from JPL Small-Body Database)

Star Occultation

On the morning of January 26, 2007 the occultation of the star 32 Lyncis by 372 Palma was observed.

The observations can be fit to an ellipse with dimensions 207 kilometers by 184 kilometers, to an accuracy of +/-2 km.

Moons of outer solar system - S/2007 (148780) 1 (moon of Altjira)

S/2007(148780)1, is a retrograde natural satellite of 148780 Altjira, which is a binary classical Kuiper belt object (cubewano).

S/2007(148780)1, is large compared to the primary, estimated diameter 246 km vs 340 km.

S/2007(148780)1 is the 25th largest moon in the Solar System currently known.

Discovery

S/2007(148780)1 was reported in March 2007.

Naming

Upon discovery, the moon was issued a provisional designation, S/2007 (148780)1.

Stats

Diameter (estimated): 246 km (200 - 360 km)

Semi-major axis: 9904 ± 56 km

Orbital Period: 139.56 days

Rotation Period: ?

How big is it?

Altjira and S/2007(148780)1 are so far away in the outer solar system that we don't know for sure how large they are. 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.

(28978) Ixion - 24th Largest TNO? 4th Largest Plutino ?

28978 Ixion is a trans-Neptunian object in the Kuiper belt. It is considered to be a dwarf planet by some astronomers, but the IAU has not formally designated it as such.

Ixion is possibly the 24th largest TNO and 4th largest Plutino currently known.

Discovery

Ixion was discovered on May 22, 2001 by Deep Ecliptic Survey (DES) at the Cerro Tololo Inter-American Observatory in the Atacama Desert of northern Chile.

Other than Pluto, Ixion was the first TNO discovered that was originally estimated to be larger than asteroid Ceres. Even in 2002, a year after its discovery, Ixion was still believed to be more than 1000 km in diameter. More recent estimates suggest that Ixion has a high albedo and is smaller than Ceres. Observations of Ixion by Spitzer Space Telescope in the far-infrared part of the spectrum revealed that its size is about 650 km.

Naming

Ixion the TNO is named after Ixion, a figure from Greek mythology. The name was suggested by E. K. Elliot.

In Greek mythology, Ixion was king of the Lapiths, the most ancient tribe of Thessaly. By killing his father-in-law, Ixion was reckoned the first man guilty of kin-slaying in Greek mythology. That alone would warrant him a terrible punishment.

However, Zeus had pity on Ixion and brought him to Olympus and introduced him at the table of the gods. Instead of being grateful, Ixion grew lustful for Hera, Zeus's wife, a further violation of guest-host relations.

Zeus thwarted this by creating the cloud Nephele, which resembled Hera and by whom Ixion fathered the Centaurs. For his crimes Ixion was bound to a wheel that turns forever in the underworld.

Stats

Estimated Diameter: 650 km (430 – 910 km)
Aphelion: 49.27 AU
Perihelion: 29.73 AU
Semi-major axis: 39.42 AU
Orbital Period: 247.53 years
Rotation period: ? hrs
Date discovered: 2001.5.22
Satellite: 0
Classification: TNO, KBO - Plutino

Orbit

Ixion is a plutino, locked in a 2:3 resonance with Neptune, making two revolutions around the Sun, while Neptune makes three.

Ixion and Pluto follow similar but differently oriented orbits: Ixion’s perihelion is below the ecliptic whereas Pluto's is above it. Uncharacteristically for bodies locked in resonance with Neptune (such as Orcus), Ixion approaches Pluto with less than 20 degrees of angular separation.

Ixion is currently crossing the ecliptic heading below, and will reach its perihelion in 2070. Pluto has passed its perihelion (1989) and is descending toward the ecliptic.

Ixion does demonstrate some regular changes in brightness, which are thought to be caused by its rotation. As of 2010, however, the rotation period of Ixion remains undetermined.

Physical characteristics

Ixion is moderately red in visible light and has a surface made of a mixture of tholin and water ice.

Ixion has a higher albedo (>0.15) than the mid-sized red cubewanos. There may be an absorption feature at the wavelength of 0.8 μm in its spectrum, which is commonly attributed to the alteration of surface materials by water.

Both visible and infrared spectroscopic results indicate that Ixion's surface is a mixture of water ice, dark carbon and tholin, which is a heteropolymer formed by irradiation of clathrates of water and organic compounds.

The Very Large Telescope (VLT) has checked Ixion for cometary activity, but did not detect a coma. Ixion is currently about 41 AU from the Sun, and it is possible that Ixion could develop a coma or temporary atmosphere when it is closer to perihelion.

How big is it?

Ixion 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.

2010 KZ39 - 23th Largest TNO? 10th Largest Cubewano ?

2010 KZ39 is a large trans-Neptunian object. 2010 KZ39 is possibly the 23th largest TNO and 10th largest Cubewano currently known.

Discovery

2010 KZ39 was discovered by Andrzej Udalski, Scott S. Sheppard, M. Szymanski and Chad Trujillo on May 21, 2010 at Las Campanas Observatory, located in the southern Atacama Desert of Chile.

2010 KZ39 has been observed 19 times over two oppositions.

Stats

Estimated Diameter: 661 km (440 – 980 km)
Aphelion: 52.5 AU
Perihelion: 39.11 AU
Semi-major axis: 45.75 AU
Orbital Period: 309.44 years
Rotation period: ?
Date discovered: 2010.5.21
Satellite: ?
Classification: TNO, KBO - Cubewano

Orbit

2010 KZ39 is currently 46.3 AU from the Sun. Using the best-fit values for its orbit it is expected to come to perihelion in 2085.

Physical Characteristics

Very little is known about 2010 KZ39.

How big is it?

2010 KZ39 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.

Dwarf planet candidate?

Assuming a generic trans-Neptunian albedo of 0.09, it would be about 735 km in diameter. But since its albedo is unknown and it has a preliminary absolute magnitude of 3.9, it could easily be somewhere between 440 (albedo: 0.25) and 980 km (albedo: 0.05) in diameter.

Mike Brown's automatically updated website lists it as a highly likely dwarf planet.

(145452) 2005 RN43 - 22th Largest TNO? 9th Largest Cubewano ?

2005 RN43 is a large trans-Neptunian object. 2005 RN43 is possibly the 22th largest TNO and 9th largest Cubewano currently known.

Discovery

2005 RN43 was discovered by Andrew C. Becker, Andrew W. Puckett and Jeremy M. Kubica on September 10, 2005 at Apache Point Observatory in Sunspot, New Mexico.

2005 RN43 has been observed 119 times over 13 oppositions with precovery images back to 1954.

Stats

Estimated Diameter: 661 km
Aphelion: 42.55 AU
Perihelion: 40.55 AU
Semi-major axis: 41.61 AU
Orbital Period: 268.45 years
Rotation period: 5.62 hours
Date discovered: 2005.9.10
Satellite: 0
Classification: TNO, KBO - Cubewano

Classification

The Minor Planet Center (MPC) classifies it as a cubewano. But since 2005 RN43 has an inclination of 19.3°, and it is unknown how it acquired this moderate inclination, the Deep Ecliptic Survey (DES) classifies it as scattered-extended.

Physical Characteristics

Very little is known about 2005 RN43.

How big is it?

2005 RN43 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.

Dwarf planet candidate?

2005 RN43 is very likely a dwarf planet. Mike Brown's automatically updated website lists it as a highly likely dwarf planet, but the diameter of the object has never been measured.

(90568) 2004 GV9 - 21th Largest TNO? 8th Largest Cubewano ?

2004 GV9 is a large trans-Neptunian object. 2004 GV9 is possibly the 21th largest TNO and 8th largest Cubewano currently known.

Discovery

2004 GV9 was discovered on April 13, 2004, by the Near-Earth Asteroid Tracking (NEAT) at Palomar.

2004 GV9 has been observed 47 times with precovery images back to 1954.

Stats

Estimated Diameter: 677 km (677 ± 70 km)
Aphelion: 45.74 AU
Perihelion: 38.7 AU
Semi-major axis: 41.81 AU
Orbital Period: 270.37 years
Rotation period: 5.86 hours
Date discovered: 2004.4.13
Satellite: 0
Classification: TNO, KBO - Cubewano

Physical Characteristics

Very little is known about 2004 GV9.

How big is it?

2004 GV9 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.

Dwarf planet candidate?

2004 GV9 is very likely a dwarf planet. The Spitzer Space Telescope has estimated it to have a diameter of 677 ± 70 km. Light-curve-amplitude analysis shows only small deviations, suggesting that 2004 GV9 could be a spheroid with small albedo spots and hence a dwarf planet.

2010 EK139 - 20th Largest TNO?

2010 EK139 is a large, 2:7 resonant trans-Neptunian object.

Discovery

2010 EK139 was discovered on March 13, 2010 by astronomers from the OGLE team led by Andrzej Udalski from Warsaw University.

There are precovery images dating back to 2002.

Stats

Estimated Diameter: 677 km (462 – 1033 km)
Aphelion: 106.25 AU
Perihelion: 32.49 AU
Semi-major axis: 68.91 AU
Orbital Period: 572 years
Rotation period: ? hrs
Date discovered: 2010.3.13
Satellite: 0
Classification: TNO, 2:7 resonance

Orbit

2010 EK139 will come to perihelion around 2038, and is currently 39.1 AU from the Sun.

2010 EK139 has been observed 122 times over 5 oppositions and has an orbit quality of 2 [JPL ranks orbital quality from 0 to 9 (0 being best)].

A ten million year integration of the orbit shows that 2010 EK139 may be in a 7:2 resonance with Neptune.

How big is it?

2010 EK139 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.

Dwarf-planet candidate

Assuming a generic trans-Neptunian albedo of 0.09, but since the true albedo is unknown and it has an absolute magnitude of 3.8, 2010 EK139 could easily be from about 462 to 1033 km in diameter.

Mike Brown lists 2010 EK139 as highly likely dwarf planet.

2006 QH181 - 19th Largest TNO? 5th Largest SDO ?

2006 QH181 is a large trans-Neptunian object. 2006 QH181 is possibly the 19th largest TNO and 5th largest SDO currently known.

Discovery

2006 QH181 was discovered on August 21, 2006. The discover was not known.

Stats

Estimated Diameter: 677 km (460 - 1030 km)
Aphelion: 97.02 AU
Perihelion: 38.24 AU
Semi-major axis: 67.71 AU
Orbital Period: 557.16 years
Rotation period: ?
Date discovered: 2006.8.21
Classification: TNO, SDO, 1:5 resonance?

Orbit

2006 QH181 came to perihelion around 1859. 2006 QH181 is currently 82.7 AU from the Sun. The only dwarf-planet-type bodies currently further from the Sun are Eris (96 AU), Sedna (87 AU) and 2007 OR10 (86 AU). Being so far from the Sun, it only has an apparent magnitude of 23.

2006 QH181 has been observed 10 times over only 2 oppositions and thus currently has a poorly known orbit. JPL ranks orbital quality from 0 to 9 (0 being best), and 2006 QH181 is currently listed with a poor orbital quality of 8.

2006 QH181 could be part of the scattered disc. 2006 QH181 may be a detached object since a perihelion of 38.24 AU may place it outside of the direct influence of Neptune, or it could have a 5:1 resonance with Neptune. Further observations of the orbit will be required.

How big is it?

2006 QH181 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.

Dwarf-planet candidate

Mike Brown lists 2006 QH181 as highly likely dwarf planet.

12th Largest Moon of Neptune - Laomedeia (11th Moon outwards from Neptune)

Laomedeia is a prograde irregular satellite of Neptune.

Laomedeia is the 12th largest satellite of Neptune and 71th largest moon in the Solar System currently known.

Discovery

Laomedeia was discovered 13 August 2002 by Matthew J. Holman, John J. Kavelaars, Tommy Grav, Wesley C. Fraser and Dan Milisavljevic using images taken by the 4.0-m Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile and the 3.6-m Canada-France-Hawaii Telescope in Hawaii. Multiple images were digitally combined until stars appeared as streaks, while the moons appeared as points of light.

Laomedeia is so distant and so small it is about 100 million times fainter than can be seen with the unaided eye. Laomedeia was missed by the Voyager 2 spacecraft in 1989 because it is so faint and distant from Neptune.

Naming

The moon was given the temporary designation S/2002 N3.

Laomedeia the moon is named after one of the Nereids, the fifty daughters of Nereus and Doris. Laomedeia was The Nereid "leader of the folk".

Orbit

Laomedeia is considered an irregular satellite because of its distant, eccentric orbit around Neptune. Like most irregular satellites of the giant planets in our outer solar system, Laomedeia most likely formed after a collision between a larger moon and a comet or an asteroid.

Physical characteristics

Very little is known about Laomedeia.

Laomedeia is about 42 kilometers in diameter (assuming an albedo of 0.04).

12th Largest Moon of Uranus - Rosalind (8th Moon outwards from Uranus)

Rosalind is an inner satellite of the planet Uranus.

Rosalind is the 12th largest Moon of Uranus and the 56th largest moon in the Solar System currently known.

Discovery

Rosalind 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 U4.

The moon was named after the daughter of the banished Duke in William Shakespeare's play "As You Like It".

As You Like It is a pastoral comedy by William Shakespeare believed to have been written in 1599 or early 1600.

As You Like It follows its heroine Rosalind as she flees persecution in her uncle's court, accompanied by her cousin Celia and Touchstone the court jester, to find safety and eventually love in the Forest of Arden. Historically, critical response has varied, with some critics finding the work of lesser quality than other Shakespearean works and some finding the play a work of great merit.

Stats

Diameter (mean): 72 ± 12 km

Semi-major axis: 69,927 km

Orbital Period: 0.558 days

Orbit

Rosalind 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.

Rosalind belongs to a group of satellites called the Portia Group, which includes Bianca, Cressida, Desdemona, Portia, Juliet, Cupid, Belinda and Perdita. These satellites have similar orbits and photometric properties.

Rosalind is very close to a 3:5 orbital resonance with Cordelia.

Physical characteristics

Other than its orbit, diameter of 72 km and geometric albedo of 0.08, virtually nothing is known about Rosalind.

In the Voyager 2 images Rosalind appears as an almost spherical object. The ratio of axes of Rosalind's prolate spheroid is 0.8-1.0. Its surface is grey in color.

Exploration Status

No close-up image of Rosalind has been photographed.

No mission is planned in the foreseeable future.

12th Largest Moon of Saturn - Prometheus (4th Moon outwards from Saturn)

Prometheus is an inner satellite of Saturn.


Prometheus is the 12th largest moon of Saturn, and the 49th largest moon in the Solar System currently known.


Discovery

Prometheus was discovered in 1980 (some time before October 25) from photos taken by the Voyager 1 probe.



Naming

Prometheus was provisionally designated S/1980 S27. In late 1985, the moon was officially named after Prometheus, a Titan in Greek mythology.

In Greek mythology, Prometheus is a Titan, the son of Iapetus and Clymene, and brother to Atlas, Epimetheus and Menoetius. He was a champion of mankind, known for his wily intelligence, who stole fire from Zeus and gave it to mortals. Zeus then punished him for his crime by having him bound to a rock while a great eagle ate his liver every day only to have it grow back to be eaten again the next day. His myth has been treated by a number of ancient sources, in which Prometheus is credited with – or blamed for – playing a pivotal role in the early history of mankind.

Stats

Diameter (mean): 86.2 ± 5.4 km

Semi-major axis: 139,380 km

Orbital Period: 0.613 days

Orbit

Prometheus rotates synchronously with its orbital period, keeping one face pointed toward Saturn.

Prometheus acts as a shepherd satellite for the inner edge of Saturn's F Ring. Recent images from the Cassini probe show that the Promethean gravitational field creates kinks and knots in the F Ring as the moon 'steals' material from it.

The orbit of Prometheus appears to be chaotic, as a consequence of a series of four 121:118 mean motion resonances with Pandora. The most appreciable changes in their orbits occur approximately every 6.2 years, when the periapsis of Pandora lines up with the apoapsis of Prometheus and the moons approach to within about 1400 km.

Prometheus is itself a significant perturber of Atlas, with which it is in a 53:54 mean longitude resonance.

Physical Characteristics

Prometheus is extremely elongated, measuring about 136 by 79 by 59 km. It has several ridges and valleys and a number of impact craters of about 20 km diameter are visible, but it is less cratered than nearby Pandora, Epimetheus and Janus.

From its very low density and relatively high albedo, it seems likely that Prometheus is a very porous icy body. There is a lot of uncertainty in these values, however, and so this remains to be confirmed.

12th Largest Moon of Jupiter - Sinope (62th Moon outwards from Jupiter)

Sinope is a retrograde irregular satellite of Jupiter and was the outermost known moon of Jupiter until the discovery of Megaclite in 2000. The most distant moon of Jupiter now known is S/2003 J2.

Sinope is the 12th largest moon of Jupiter and 74th largest moon in the Solar System currently known.

Discovery

Sinope was discovered by Seth Barnes Nicholson at Lick Observatory on July 21, 1914.

Naming

Sinope the moon is named after Sinope of Greek mythology.

In Greek Mythology, Sinope was one of the daughters of Asopus and thought to be an eponym of the city Sinope on the Black Sea.

According to Corinna and Diodorus Siculus, Sinope was seized by the god Apollo and carried over to the place where later stood the city honouring her name. Diodorus adds that she bore to Apollo a son named Syrus, supposedly afterwards king of the Syrians, who were named after him.

However, the Argonautica and Valerius Flaccus relate that Sinope was abducted to the site by Zeus, who, in his passion, swore to fulfil her dearest wish. Sinope declared she wished to remain a virgin. Sinope later tricked Apollo and the river Halys in the same fashion and remained a virgin all her life.

Stats

Diameter (mean): 38 km

Semi-major axis: 24,057,865 km

Orbital Period: -762.33 day

Orbit

Sinope orbits Jupiter on a high eccentricity and high inclination retrograde orbit. The orbital elements are as of January 2000. They are continuously changing due to solar and planetary perturbations.

It is often believed to belong to the Pasiphaë group. However, given its mean inclination and different colour, Sinope could be also an independent object, captured independently, unrelated to the collision and break-up at the origin of the group.

Sinope is also known to be in a secular resonance with Jupiter, similar to Pasiphae. However, Sinope can drop out of this resonance and has periods of both resonant and non resonant behaviour.

Physical characteristics

Sinope has an estimated diameter of 38 km (assuming an albedo of 0.04). The satellite is red, unlike Pasiphae which is grey.

Its infrared spectrum is similar to D-type asteroids and also different from Pasiphae. These dissimilarities of the physical parameters suggest a different origin from the core members of the group.

Moon of 121 Hermione -- S/2002 (121) 1 "LaFayette"

The moon of 121 Hermione is the 6th largest moon of the asteroids currently known.

Discovery

The moon of 121 Hermione was discovered 28 September 2002 by W. J. Merline, P. M. Tamblyn, C. Dumas, L. M. Close, C. R. Chapman, F. Menard, W. M. Owen, D. C. Slater and J. Pepin using the Keck II telescope at Mauna Kea.

Naming

The moon was given the temporary designation S/2002 (121) 1, but has not yet received an official name.

"LaFayette" has been proposed by a group of astronomers in reference to the frigate used in secret by the Marquis de Lafayette to reach America to help the insurgents.

Stats

Diameter (estimated): 12 km (12 ± 4 km)

Semi-major axis: 768 ± 11 km

Orbital Period: 2.58 days

Rotation period: ?

30th Largest Asteroid, 121 Hermione

121 Hermione is a large asteroid in the outer main asteroid belt. It is the 30th largest asteroid currently known.

Discovery

Hermione was discovered by James Craig Watson on May 12, 1872 from Ann Arbor, Michigan, USA.

Naming

Hermione the asteroid was named after Hermione, daughter of Menelaus and Helen in Greek mythology.

In Greek mythology, Menelaus was a legendary king of Mycenaean Sparta, the husband of Helen of Troy, and a central figure in the Trojan War.

Helen of Troy, also known as Helen of Sparta, was the daughter of Zeus and Leda (or Nemesis), step-daughter of King Tyndareus and wife of Menelaus. Her abduction by Paris brought about the Trojan War.

Stats

Diameter (mean): 190 km
Aphelion: 3.933 AU
Perihelion: 2.983 AU
Semi-major axis: 3.449 AU
Orbital Period: 6.41 years
Rotation period: 5.55 hrs
Date discovered: 1872.5.12
Class: C
Group: Cybele group
Type: Outer Main-belt Asteroid
Satellite: 1
(data from JPL Small-Body Database)

Orbit

Hermione is a Cybele asteroid and orbits beyond most of the main-belt asteroids.

Satellite

A satellite of Hermione was discovered in 2002 with the Keck II telescope.

Physical properties

Hermione is an asteroid of the dark C spectral type, and is probably composed of carbonaceous materials.

Hermione has a bi-lobed shape, as evidenced by adaptive optics images, the first of which were taken in December 2003, with the Keck telescope. Of several proposed shape models that agreed with the images, a "snowman"-like shape was found to best fit the observed precession rate of Hermione's satellite. In this "snowman" model, the asteroid's shape can be approximated by two partially overlapping spheres of radii 80 and 60 km, whose centers are separated by 115 km. A simple ellipsoid shape was ruled out.

Observation of the satellite's orbit has made possible an accurate determination of Hermione's mass. For the best-fit "snowman" model, the density is found to be 1.8 ± 0.2 g/cm³, giving a porosity of the order of 20%, and possibly indicating that the main components are fractured solid bodies, but that the asteroid is rather not a rubble pile.

Star Occultation

Occultations by Hermione have been successfully observed three times so far, the last time in February 16, 2004, when Hermione occulted TYC 1905-00864-1 in Gemini.

Moon of asteroid 702 Alauda -- Pichi üñëm

The moon of 702 Alauda is the 12th largest moon of the asteroids currently known.

Discovery

P . Rojo, Universidad de Chile; and J. L. Margot, Cornell University, reported the discovery on July 26, 2007 of a satellite of 702 Alauda from adaptive-optics imaging with the ESO 8-m Very Large Telescope UT4/YEPUN on Cerro Paranal, Chile.

The satellite was observed at two epochs on each of two consecutive nights. On July 26, the companion was at a separation of 0".58 (projected separation about 900 km).

The primary-to-secondary H-band flux ratio is about 1250, yielding a diameter ratio of about 35.

Naming

The moon was given the temporary designation S/2007(702)1.

The moon has been named Pichi üñëm, which means "little bird" in the Mapuche language of Chile, the country from which the moon was discovered.

Stats

Diameter (estimated): 5.5 km

Semi-major axis: 900 km

Orbital Period: 3 days ?

Rotation period: ?

29th Largest Asteroid, 702 Alauda

702 Alauda is a large asteroid and the 29th largest asteroid currently known.

Discovery

702 Alauda was discovered on 16 July 1910 by Joseph Helffrich at Heidelberg.

Naming

Alauda the asteroid was named after the Alaudidae family of birds (the larks).

Larks are passerine birds of the family Alaudidae. All species occur in the Old World, and in northern and eastern Australia; only one, the Shore Lark, has spread to North America, where it is called the Horned Lark.

Stats

Diameter (mean): 195 km
Aphelion: 3.261 AU
Perihelion: 3.129 AU
Semi-major axis: 3.195 AU
Orbital Period: 5.71 years
Rotation period: 8.35 hrs
Date discovered: 1910.7.16
Class: C
Satellite: 1
Group: Alauda Group
Type: Main-belt Asteroid
(data from JPL Small-Body Database)

Satellite

Alauda's satellite, Pichi üñëm, was discovered in 2007 from observations using adaptive-optics imaging with the European Southern Observatory (ESO) 8-m Very Large Telescope (VLT) on Cerro Paranal, Chile.

Orbital characteristics

Alauda has been identified as the largest member of a dynamical family. Alauda's moon may be a result of the collision that created the asteroid family.

Physical characteristics

The discovery of Alauda's moon enabled Alauda's mass to be determined. Rojo and Margot (2010) have estimated its mass to be 6.06×1018 kg with a density of 1.57 g/cm³.

Star Occultations

Alauda has been observed to occult stars on several occasions, providing important information on its size and shape. Alauda produced occultations on 2001-07-12 (on SAO 188447) and 2009-10-17 (on TYC 1920-00620-1).

28th Largest Asteroid, 24 Themis

24 Themis is a large main-belt asteroids and the largest member of the Themistian asteroid family. Themis is the 28th largest asteroid currently known.

Discovery

24 Themis was discovered on 5 April 1853 by Annibale de Gasparis at Naples.

Naming

Themis the asteroid was named after Themis, the Greek goddess of law.

Themis is an ancient Greek Titaness. She is described as "of good counsel", and is the embodiment of divine order, law and custom.

Themis was named by Angelo Secchi, who was Director of the Observatory at the Pontifical Gregorian University (then called the Roman College). He was a pioneer in astronomical spectroscopy, and was one of the first scientists to state authoritatively that the Sun is a star.

Stats

Diameter (mean): 198 km
Aphelion: 3.539 AU
Perihelion: 2.732 AU
Semi-major axis: 3.316 AU
Orbital Period: 5.55 years
Rotation period: 8.37 hrs
Date discovered: 1853.4.5
Class: C
Group: Themis Group
Type: Main-belt Asteroid
(data from JPL Small-Body Database)

Orbit and rotation

Themis is in an elliptical orbit around the Sun with an eccentricity of 0.1306 and an inclination of 0.76°.

Themis is part of the Themis family of asteroids, which is located in the outer part of the main belt. The family consists of a core of large objects surrounded by a cloud of smaller objects; 24 Themis is a member of the core.

Surface ice

On October 7, 2009, the presence of water ice was confirmed on the surface of Themis using NASA’s Infrared Telescope Facility. The surface of Themis appears completely covered in ice. As this ice layer is sublimated, it may be getting replenished by a reservoir of ice under the surface. Organic compounds were also detected on the surface.

Scientists hypothesize that some of the first water brought to Earth was delivered by asteroid impacts after the collision that produced the Moon. The presence of ice on 24 Themis supports this theory. Because of its proximity to the sun (~3.3 AU), the widespread ice on the surface of 24 Themis is somewhat unexpected. The surface ice may be replenished by a sub-surface reservoir of water.

An alternative mechanism to explain the presence of water ice on Themis is similar to the hypothesized formation of water on the surface of the Moon by solar wind. Trace amounts of water would be continuously produced by high-energy solar protons impinging oxide minerals present at the surface of Themis.

27th Largest Asteroid, 7 Iris

7 Iris is a large main-belt asteroid and is the 27th largest asteroid currently known.

Among the S-type asteroids, it ranks fifth in geometric mean diameter after Eunomia, Juno, Herculina and Amphitrite.

Discovery

Iris was the seventh asteroid discovered, on August 13, 1847, by John Russell Hind from London. Iris was Hind's first asteroid discovery.

Naming

Iris was named after the rainbow goddess Iris of Greek mythology, sister of the Harpies and messenger of the gods, especially Hera. Her quality of attendant of Hera was particularly appropriate to the circumstances of discovery, as Iris was spotted following 3 Juno (Juno is the Roman equivalent of Hera) by less than an hour of right ascension.

In Greek mythology, Iris is the personification of the rainbow and messenger of the gods. She is also known as one of the goddesses of the sea and the sky. Iris links the gods to humanity. She travels with the speed of wind from one end of the world to the other, and into the depths of the sea and the underworld.

Stats

Diameter (mean): 200 km
Aphelion: 2.937 AU
Perihelion: 1.824 AU
Semi-major axis: 2.387 AU
Orbital Period: 3.69 years
Rotation period: 7.139 hrs
Date discovered: 1847.8.13
Class: S
Type: Main-belt Asteroid
(data from JPL Small-Body Database)

Brightness

Iris's bright surface and small distance from the Sun make it the fourth brightest object in the asteroid belt after Vesta, Ceres, and Pallas. But at typical oppositions it marginally outshines the larger though darker Pallas.

Iris has a mean opposition magnitude of +7.8, comparable to that of Neptune, and can easily be seen with binoculars at most oppositions. At rare oppositions near perihelion Iris can reach a magnitude of +6.7 (next time on October 31st, 2017 reaching a magnitude of +6.9), which is as bright as Ceres ever gets. Reports of Iris being seen without optical aid are unverified.

Characteristics

Lightcurve analysis indicates a somewhat angular shape and that Iris' pole points towards ecliptic coordinates with a 10° uncertainty. This gives an axial tilt of 85°, so that on almost a whole hemisphere of Iris, the sun does not set during summer, and does not rise during winter. On an airless body this gives rise to very large temperature differences.

The Iridian surface likely exhibits albedo differences, with possibly a large bright area in the northern hemisphere. Overall the surface is very bright and is probably a mixture nickel-iron metals and magnesium- and iron-silicates. Its spectrum is similar to that of L and LL chondrites with corrections for space weathering, so it may be an important contributor of these meteorites. Planetary dynamics also indicates that it should be a significant source of meteorites.

Star Occultation

Iris was observed occulting a star on May 26, 1995, and later on July 25, 1997. Both observations gave a diameter of about 200 km.

Moon of asteroid 624 Hektor -- S/2006 (624) 1

The moon of 624 Hektor is the 4th largest moon of the asteroids currently known.

Discovery

On 16 July 2006, a satellite of Hektor was found by F. Marchis, M. H. Wong, J. Berthier, P. Descamps, D. Hestroffer, F. Vachier, D. Le Mignant and I. de Pater based on observations from the Keck-II adaptive optics telescope.

Naming

The moon was given the temporary designation S/2006(624)1, but has not yet received an official name.

Stats

Diameter (estimated): 15 km

Semi-major axis: 1000 km

Orbital Period: 2.08 days

Rotation period: ?

26th Largest Asteroid, 624 Hektor [Largest Jupiter Trojan]

624 Hektor is the largest Jupiter Trojan and is the 26th largest asteroid currently known.

Discovery

624 Hektor was discovered on Feb 10, 1907 by August Kopff at Heidelberg.

Naming

Hektor is named after the Trojan hero Hektor.

In Greek mythology, Hectōr or Hektōr, was a Trojan prince and the greatest fighter for Troy in the Trojan War. He acts as leader of the Trojans and their allies in the defense of Troy, killing 31 Greek fighters in all.

Stats

Diameter (mean): 203 km
Aphelion: 5.349 AU
Perihelion: 5.121 AU
Semi-major axis: 5.243 AU
Orbital Period: 12.01 years
Rotation period: 6.924 hrs
Date discovered: 1907.2.10
Class: D
Satellite: 1
Type: Jupiter Trojan
(data from JPL Small-Body Database)

Orbit

Hektor is a D-type asteroid, dark and reddish in colour. It lies in Jupiter's leading Lagrangian point, L4, called the 'Greek' node after one of the two sides in the legendary Trojan War.

Hektor is thus one of two trojan asteroids that is "misplaced" in the wrong camp (the other being 617 Patroclus in the Trojan node).

Formation

Hektor is found to be a truly extraordinary object in that it is larger and far more irregular in shape than other measured Trojans and far more irregular than other belt asteroids of comparable size.

It is proposed that Hektor could be a partially coalesced pair of Trojan asteroids which collided with energy too low to cause complete fragmentation, thus forming a dumbbell-shaped object.

Contact binary plus moonlet

Hektor is one of the most elongated bodies of its size in the Solar System, being 370 × 200 km. It is thought that Hektor might be a contact binary. Hubble Space Telescope observations of Hektor in 1993 did not show an obvious bilobate shape because of a limited angular resolution.

On 17 July 2006, the Keck-10m II telescope and its Laser guide star Adaptive Optics (AO) system indicated a bilobate shape for Hektor.

Additionally, a 15-km moonlet at 1000 km of Hektor was detected. The satellite's provisional designation is S/2006(624)1.

Hektor is, so far, the only known binary trojan asteroid in the L4 point and the first trojan with a satellite companion.

Moons of outer solar system - Vanth (moon of Orcus)

Vanth, officially (90482) Orcus I Vanth, is the single known natural satellite of the plutino and likely dwarf planet Orcus.

Vanth is the 23th largest moon in the Solar System currently known.

Discovery

Vanth was discovered by Mike Brown and T.-A. Suer using discovery images taken by the Hubble Space Telescope on November 13, 2005. The discovery was announced on 22 February, 2007 in IAUC 8812.

Naming

Upon discovery, Vanth was issued a provisional designation, S/2005 (90482) 1. On March 23, 2009, Brown asked readers of his weekly column to suggest possible names for the satellite, with the best one to be submitted to the International Astronomical Union (IAU) on April 5.

The name Vanth, the winged Etruscan psychopomp who guides the souls of the dead to the underworld, was chosen from among a large pool of submissions.

Vanth was the only suggestion that was purely Etruscan in origin. It was the most popular submission, first suggested by Sonya Taaffe.

The Etruscan Vanth is frequently portrayed in the company of Charun (Charon), and so as the name of the moon of Orcus (nicknamed the "anti-Pluto" because resonance with Neptune keeps it on the opposite side of the Sun from Pluto), it is an allusion to the parallels between Orcus and Pluto.

Stats

Diameter (estimated): 280 km (280 - 380 km)

Semi-major axis: 9030 ± 89 km

Orbital Period: 9.54 days

Rotation Period: Synchronous

Orbit

Vanth orbits Orcus "in a tight precise circle", with a period of approximately 10 days.

Michael E. Brown suspects that, like Pluto and Charon, Orcus and Vanth are tidally locked.

Formation

The satellite does not resemble other known collisional satellites because its spectrum is very different of that of primary and thus may be a captured KBO.

Physical Properties

Vanth was found at 0.25 arcsec from Orcus with magnitude difference of 2.7 ± 1.0. Estimates made in 2009 by Mike Brown show that the apparent magnitude of Vanth is 21.97 ± 0.05 which is 2.54 ± 0.01 magnitudes fainter than Orcus. Assuming equal albedos this would mean a diameter of 280 km, or 2.9 times smaller than the primary.

However, the dissimilar colors of Orcus (neutral) and Vanth (red) suggest that Vanth could have an albedo a factor of two lower than Orcus. Should Vanth have an albedo of only 0.12, Vanth could be as large as 380 km with Orcus being 760 km in diameter. The mass of Vanth also depends on its albedo and can vary from 3 to 9% of the total system mass.

(55637) 2002 UX25 - 18th Largest TNO? 7th Largest Cubewano ?

2002 UX25 is a large trans-Neptunian object. 2002 UX25 is possibly the 18th largest TNO and 7th largest Cubewano currently known.

Discovery

2002 UX25 was discovered on October 30, 2002, by the Spacewatch program at Kitt Peak.

2002 UX25 has precovery images back to 1991.

Stats

Estimated Diameter: 681 km (567 - 797 km)
Aphelion: 48.92 AU
Perihelion: 36.77 AU
Semi-major axis: 42.94 AU
Orbital Period: 281.41 years
Rotation period: 14.38 hours
Date discovered: 2002.10.30
Satellite: 1
Classification: TNO, KBO - Cubewano

Orbit

2002 UX25 is a Spitzer dwarf-planet candidate that orbits the Sun in the Kuiper belt beyond Neptune. It takes roughly 281 years to orbit the Sun.

2002 UX25 has a perihelion (closest approach to the Sun) of 36.77 AU, which it will next reach in 2065. As of 2010, 2002 UX25 is 41 AU from the Sun.

Physical Characteristics

A variability of the visual brightness was detected which could be fit to a period of 14.38 or 16.78 h rotation period (depending on a single-peaked or double peaked curve).

The Spitzer Space Telescope has estimated it to have a size of 681 +116 or
−114 km.

Satellite

The discovery of a satellite of 2002 UX25 was reported in IAUC 8812 on 22 February 2007.

The satellite was detected using the Hubble Space Telescope in August 2005. The orbit of this satellite has yet to be determined. The satellite was found at 0.16 arcsec from the primary with an apparent magnitude difference of 2.5. Assuming a similar albedo the magnitude suggests the satellite has a diameter of 205 ± 55 km.

How big is it?

2002 UX25 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.

Dwarf planet candidate?

2002 UX25 has an absolute magnitude of 3.6, making it a dwarf planet candidate. The Spitzer Space Telescope has estimated 2002 UX25 to have a diameter of about 681 km, and most icy objects around 400 km in diameter are believed to be spherical.

Michael E. Brown's automatically updated website lists it as a highly likely dwarf planet, and Michael E. Brown called it a probable dwarf planet. But light curve analysis has questioned whether it would truly qualify as a dwarf planet.

(208996) 2003 AZ84 - 17th Largest TNO? 3rd Largest Plutino ?

(208996) 2003 AZ84, is a plutino, like Pluto, in a 2:3 resonance with Neptune. 2003 AZ84 is possibly the 17th largest TNO and 3rd largest Plutino currently known.

Discovery

2003 AZ84 was discovered on January 13, 2003 by Michael E. Brown and Chadwick A. Trujillo using the Samuel Oschin telescope in the Palomar Observatory.

Stats

Estimated Diameter: 685 km (686 ± 96 km)
Aphelion: 46.48 AU
Perihelion: 32.61 AU
Semi-major axis: 39.56 AU
Orbital Period: 248.81 years
Rotation period: 13.42 hours
Date discovered: 2003.1.13
Satellite: 1 ?
Classification: TNO, KBO - Plutino

Orbit

2003 AZ84 is classified as a plutino, which means that it is in a 3:2 orbital resonance with Neptune, similar to that of Pluto. It orbits the Sun in just over 248 Earth years.

2003 AZ84 is currently 45.3 AU from the Sun and came to aphelion (farthest distance from the Sun) in 1982. It will come to perihelion in 2107.

Physical characteristics

The Spitzer Space Telescope has estimated 2003 AZ84 to have a size of 686 ± 96 km, while an analysis of a combination of Spitzer and Hershel data yielded a somewhat higher estimate of 910 ± 60 km.

The spectra and colors of 2003 AZ84 are very similar to those of Orcus, another large planetoid in 3:2 resonance with Neptune. Both bodies have a flat featureless spectrum in the visible and moderately strong water ice absorption bands in the near-infrared, although 2003 AZ84 has a lower albedo. Both bodies also have a weak absorption band near 2.3 μm, which may be caused by ammonia hydrate or methane ice.

A stellar occultation in 2010 measured a single chord of 573 ± 21 km. But this is only a lower limit for the diameter of 2003 AZ84 as the chord may not have passed through the center of the body.

Satellite

Using observations with the Hubble Space Telescope, the discovery of a satellite of 2003 AZ84 was reported in IAUC 8812 on 22 February 2007.

The object was measured with a separation of 0.22 arcsec and an apparent magnitude difference of 5.0.

As of 2012, attempts to recover the satellite have failed. The unrecovered satellite is estimated to be about 68 ± 20 km in diameter.

How big is it?

2003 AZ84 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.

(278361) 2007 JJ43 - 16th Largest TNO?

(278361) 2007 JJ43 is a large trans-Neptunian object (TNO). 2007 JJ43 is possibly the 16th largest TNO currently known.

Discovery

2007 JJ43's discovery images were taken on May 14, 2007 at Palomar Observatory.

Stats

Estimated Diameter: 694 km (650 - 800 km)
Aphelion: 55.37 AU
Perihelion: 40.29 AU
Semi-major axis: 47.8 AU
Orbital Period: 330.53 years
Rotation period: ? hours
Date discovered: 2007.5.14
Satellite: ?
Classification: TNO, other

Orbit

2007 JJ43 is orbiting the Sun near the outer edge of the Kuiper belt. As of 2012, 2007 JJ43 is about 41.5 AU from the Sun.

How big is it?

2007 JJ43 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.

Dwarf-planet candidate

2007 JJ43's absolute magnitude of 3.7 is one of the twenty brightest exhibited by TNOs. Assuming it has a typical albedo, this would make it roughly the same size as Ixion (~650–800 km diameter).

Mike Brown's automatically updated website lists it as a highly likely dwarf planet, but the diameter of the object has never been measured.

(307261) 2002 MS4 - 15th Largest TNO? 6th Largest Cubewano ?

2002 MS4 is a large trans-Neptunian object. 2002 MS4 is possibly the 15th largest TNO and 6th largest Cubewano currently known.

Discovery

2002 MS4 is discovered on June 18, 2002 by Michael E. Brown and Chadwick A. Trujillo at Palomar Observatory.

2002 MS4 has precovery images back to 1954.

Stats

Estimated Diameter: 726 km (603 - 849 km)
Aphelion: 47.86 AU
Perihelion: 35.51 AU
Semi-major axis: 41.67 AU
Orbital Period: 268.98 years
Rotation period: 16.34 hours
Date discovered: 2002.6.18
Satellite: ?
Classification: TNO, KBO - Cubewano

Orbit

2002 MS4 currently 47.2 AU from the Sun and will come to perihelion around 2122.

How big is it?

2002 MS4 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.

Dwarf-planet candidate

Mike Brown's automatically updated website lists it as a highly likely dwarf planet.

The Spitzer Space Telescope has estimated it to have a diameter of 726 ± 123 km.

(303775) 2005 QU182 - 14th Largest TNO? 4th Largest SDO?

2005 QU182 is a trans-Neptunian object and is possibly the 14th largest TNO and 4th largest SDO currently known.

Discovery

2005 QU182 is discovered on August 30, 2005 by Michael E. Brown, Chadwick A. Trujillo and David Lincoln Rabinowitz.

2005 QU182 has precovery images back to 1974.

Stats

Estimated Diameter: 730 km (530 - 1186 km)
Aphelion: 190.75 AU
Perihelion: 37.01 AU
Semi-major axis: 113.88 AU
Orbital Period: 1215 years
Rotation period: ? hours
Date discovered: 2005.8.30
Satellite: ?
Classification: TNO, SDO

Orbit

2005 QU182 takes over 1,200 years to orbit the Sun. Of the dwarf planets and known dwarf-planet candidates, only Sedna is known to have a longer orbit around the Sun.

2005 QU182 came to perihelion in 1971, and is currently 49 AU from the Sun.

How big is it?

2005 QU182 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.

Dwarf-planet candidate

2005 QU182 has a bright absolute magnitude of 3.5. This qualifies it as one of the largest dwarf-planet candidates. As of August 2011, Mike Brown lists it as highly likely a dwarf planet.

(55565) 2002 AW197 - 13th Largest TNO? 5th Largest Cubewano ?

2002 AW197 is a large trans-Neptunian object. 2002 AW197 is possibly the 13th largest TNO and 5th largest Cubewano currently known.

Discovery

2002 AW197 is discovered on January 10, 2002 by Michael E. Brown, Chadwick A. Trujillo, Eleanor F. Helin, Michael Hicks, Kenneth J. Lawrence and Steven H. Pravdo at Palomar Observatory.

Stats

Estimated Diameter: 734 km (626 - 850 km)
Aphelion: 53.53 AU
Perihelion: 41.07 AU
Semi-major axis: 47.28 AU
Orbital Period: 325.15 years
Rotation period: 8.86 hours
Date discovered: 2002.1.10
Satellite: ?
Classification: TNO, KBO - Cubewano

Orbit

2002 AW197 is currently 46.2 AU from the Sun and will come to perihelion around 2079.

Surface

ESO analysis of 2002 AW197 spectra reveals a strong red slope and no presence of water ice.

Dwarf-planet candidate

Measurements with the Spitzer Space Telescope have confirmed 2002 AW197 as a reliable dwarf-planet candidate, although it has not been officially classified as such by the IAU. Light-curve-amplitude analysis shows only small deviations, which suggests that 2002 AW197 is a spheroid with small albedo spots.

11th Largest Moon of Neptune - Sao (10th Moon outwards from Neptune)

Sao is a prograde irregular satellite of Neptune.

Sao is the 11th overall largest satellite of Neptune and 68th 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.

One of the satellites was Sao.

Naming

The moon was given the temporary designation S/2002 N2.

Sao the moon is named after one of the Nereids, the fifty daughters of Nereus and Doris. Sao was associated with sailing and is referred to as "The rescuer" or "Safety".

Stats

Diameter (mean): 44 km

Semi-major axis: 22,228,000 km

Orbital Period: 2912.72 days

Rotation Period: ?

Orbit

Sao follows an exceptionally inclined and moderately eccentric orbit in relation to other irregular satellites of Neptune.

Sao is in so-called Kozai resonance, i.e. its inclination and eccentricity are coupled (the inclination of the orbit decreases while eccentricity increases and vice versa).

Physical characteristics

Little is known about Sao.

Sao is about 44 kilometers in diameter (assuming an albedo of 0.04).

11th Largest Moon of Uranus - Cressida (4th Moon outwards from Uranus)

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.

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.

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.

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.

24th Largest Asteroid, 13 Egeria

13 Egeria is a large main-belt G-type asteroid and the third largest G-type asteroid after 1 Ceres and 19 Fortuna.

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.

22th Largest Asteroid, 29 Amphitrite

29 Amphitrite is one of the largest S-type asteroids, probably fourth in diameter after 15 Eunomia, 3 Juno and 532 Herculina.

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.

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: ?

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: ?