Earth's natural satellite: Formation of the Moon

The Moon is Earth's only natural satellite, and the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having a quarter the diameter of Earth and 1⁄81 its mass. Charon is larger relative to Pluto, the Pluto, at slightly more than 1/9 (11.6%) of Pluto's mass, but Pluto has been re-classified as dwarf planet.

However, the Earth and Moon are still considered a planet–satellite system, rather than a double-planet system, as their barycentre, the common centre of mass, is located 1,700 km (about a quarter of the Earth's radius) beneath the surface of the Earth.

Stats

Diameter: 3,474 km

Semi-major axis: 384,399 km

Orbital Period: 27.32 days

Formation

Several mechanisms have been proposed for the Moon's formation 4.527 ± 0.010 billion years ago, some 30–50 million years after the origin of the Solar System. These include:

1. Fission of the Moon from the Earth's crust through centrifugal forces.
-- but which would require too great an initial spin of the Earth.

2. Gravitational capture of a pre-formed Moon.
-- but which would require an unfeasibly extended atmosphere of the Earth to dissipate the energy of the passing Moon.

3. Co-formation of the Earth and Moon together.
-- but which does not explain the depletion of metallic iron in the Moon.

All these hypotheses also cannot account for the high angular momentum of the Earth–Moon system.

Giant impact hypothesis

The giant impact hypothesis proposes that the Moon was created out of the debris left over from a collision between the young Earth and a Mars-sized body. The colliding body is sometimes called Theia (or Euryphaessa) for the mythical Greek Titan who was the mother of Selene, the goddess of the moon.

The giant impact hypothesis is the current favoured scientific hypothesis for the formation of the Moon. Supporting evidence includes Moon samples which indicate the surface of the Moon was once molten, the Moon's apparently relatively small iron core and a lower density than the Earth, and evidence of similar collisions in other star systems (which result in debris disks). Further, giant collisions are consistent with the leading computer models of the formation of the solar system.

Still, there remain several unanswered questions concerning the best current models of the giant impact hypothesis. The energy of such a giant impact is predicted to heat Earth to produce a global 'ocean' of magma; yet there is no evidence of the resultant planetary differentiation of the heavier material sinking into Earth's mantle. Further, lunar samples do not have expected ratios of oxygen isotopic ratios, volatile elements, iron oxide, or siderophilic elements compared to those of Earth.

Moons of the Solar System

While the planets orbit the Sun, moons of the planets orbit the planets.

Only Mercury and Venus have no natural satellite.

Earth: 1 moon
Mars: 2 moons
Jupiter: 64 moons
Saturn: 62 moons
Uranus: 27 moons
Neptune: 13 moons

Some of the dwarf planets and asteroids also have moons:
Pluto: 4 moons
Haumea: 2 moons
Eris: 1 moon

Is the Sun a normal star?

After all the planets, I will talk about the most important member of the Solar System.

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields. It has a diameter of about 1,392,000 km, about 109 times that of Earth, and its mass (about 2×1030 kilograms, 330,000 times that of Earth) accounts for about 99.86% of the total mass of the Solar System.



The Sun is a typical G-type main-sequence star. But is it typical or normal?

Currently, the Sun is the only star known to habour life. Despite our efforts, we have yet to find an exact twin of our sun and our solar system.

There could be something very special and makes the sun the "odd" star in the universe.

Is Pluto a Planet or Not?

Planet X

Pluto was first referred to as Planet X by the astronomer Percival Lowell. He reasoned it existed because something was causing slight variations in the orbits of the planets Neptune and Uranus. He believed only another body large enough to exert a strong enough gravitational field could affect Neptune and Uranus' orbits.

Unfortunatley Percival Lowell died in 1916 without having proven the existence of Planet X. In 1930, astronomer Clyde Tombaugh discovered "Planet X" 3.7 billion miles from our sun. He did this by
using an astronomical telescope to expose a series of photographic plates. The Plates clearly showed a small object had moved against the background of distant stars.

This discovery turned out to be the result of a happy accident. The calculations that predicted the existence of a planet beyond the orbit of Neptune later proved to be in error. The Voyager 2 spacecraft was able to measure the mass of the planet Neptune more accurately. When this new data is used the variations in the orbits of Uranus and Neptune disappear.

Naming

None the less the new planet was dubbed Pluto. Several names were suggested including Zeus, Cronus and Minerva. But in 1930 Pluto was officially labeled the ninth planet by the International Astronomical Union and named for the Roman god of the underworld.

Orbit

The axis of Pluto's poles do not point "up" and "down" out of the plane of the solar system like planet Earth's. Instead the point more inward toward the Sun. Pluto is usually farther from the Sun than any of the other planets. But due to it's eccentric orbit, it is closer to the Sun than Neptune for 20 years out of its 249 year orbit. Pluto crossed inside Neptune's orbit on January 21, 1979 and made its closest approach to the Sun on September 5, 1989. It remained within the orbit of Neptune until February 11, 1999. This will not happen again until September 2226.

Pluto's odd orbit has lead some to say it is a "trans-Neptunian interloper". Which means it is more like a Kuiper belt comet than a planet.

The composition of Pluto is unknown, but its density (about 2 gm/cm3) probably indicates it is a mixture of and 30% water ice and 70% rock. The bright areas of the surface appear to be covered with ices of nitrogen and smaller amounts of methane, ethane and carbon monoxide. The composition of the darker areas on Pluto's surface is not known.

Atmosphere

Pluto does have an atmosphere which probably consists mostly of nitrogen with some carbon monoxide and methane. It is extremely thin with a surface pressure of only a few microbars. Pluto's atmosphere probably exist as a gas only when Pluto is near the Sun. For the rest of Pluto's long orbit the atmospheric gases are frozen solid. Near the Sun it is possible that some of the atmospheric gases escape into space. NASA mission planners hope to arrive at Pluto while the atmosphere is still in gas form.

Moon

In 1978 it was discovered that pluto has a moon. Officially named Charon after the mythological figure who ferried the dead across the River Acheron into the underworld. Charon was discovered by Jim Christy and may have been named in honor of his wife Charlene. Before the discovery of
Charon it was believed Pluto was much larger since the images of the two were blurred together.

Pluto and Charon are unique in that they rotate synchronously with each other. Which means they both keep the same face toward one another. It has been suggested that Charon was formed by a giant impact against Pluto similar to the one that formed Earth's Moon. In 2005 a team using
the Hubble Space Telescope discovered two tiny moons orbiting around both Pluto and Charon. They have been named Nix and Hydra. They are very small with diameters between 40 and 60 kilometers.

Recently there has been considerable debate about the classification of Pluto. It was classified as the a planet just after its discovery and remained so for 75 years. But on 2006 Aug 24 the International Astronomical Union decided to change the definition of a "planet". The new definition does not include Pluto.

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Pluto: Dwarf Planet

From young, we have learned that the Solar System has nine planets. Now, with the new classification of Dwarf Planet, the Planet Family has only eight members.

When the New Horizons Spacecraft reaches Pluto in 2015, its destination is no longer a planet.

A dwarf planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite. More explicitly, it has to have sufficient mass to overcome its compressive strength and achieve hydrostatic equilibrium.

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Interesting Facts About Neptune, By Kum Martin

Neptune is the eighth planet in our Solar System. It is positioned between Uranus and Pluto, and is sometimes called the Blue Giant. The planet is nearly 49,500 kilometers in diameter, making it nearly 4 times the size of our planet, Earth. Also, Neptune is situated around 4.4 billion kilometers from Earth, and therefore, it is not visible to naked eyes. Even using binoculars, you will not be able to see the planet clearly.

Here are some interesting facts about Neptune:

• Neptune was observed by many astronomers from ancient times. Even the great Galileo observed Neptune, but did not realize that he was looking at a planet. In ancient times, the telescopes were not powerful enough to help the researchers and astronomers discern planets. So when Neptune was seen, the astronomers could not see the disc shape of the planet.

• The planet was discovered through mathematical calculations. In the year 1843, a mathematician and astronomer from Britain was instrumental in calculating where Neptune was located. As per the calculations, it was estimated that Neptune was one billion miles further from Sun compared to Uranus.

• Another French astronomer was interested in Neptune and was calculating its position. He also has the same results as the British astronomer.

• Based on the calculations of the French astronomer, Neptune was discovered by Johann C. Galle on September 23, 1846.

• The discovery of Neptune is credited to the British astronomer as well as the French astronomer.

• As Neptune looks blue, it was named after the Roman god of sea, just like all the other planets in our Solar System are named after Roman gods.

• The core of the planet consists of iron, nickel and other silicates. While the mantle of Neptune is made up of water, methane, ammonia and other chemical compounds. The mantle of the planet is
very hot with temperature ranging from 3000 K to 5000 K.

• The atmosphere of Neptune is made up of 80 percent hydrogen, 19 percent helium, and 1 percent of ammonia, water and methane.

• The planet gets its characteristic blue color because methane present in its atmosphere absorbs the red light from the sun and then reflects it as blue into space.

• Till today, researchers and astronomers have discovered thirteen moons revolving around Neptune. It is quite possible there are still more moons waiting to be discovered.

• Voyager 2 was the first spaceship to reach Neptune in the year 1989. It took images of the planet and through these images, researchers found that the planet has five rings. These rings are called Galle, LeVerrier, Lassell, Arago and Adams. It is believed that the rings formed when one of planet's moons got too close and broke up into millions of particles as a result of Neptune's gravity.

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Uranus - The Farthest Planet That Can be Seen Without a Telescope

Uranus is the ancient Greek deity of the Heavens, the earliest supreme god. Uranus is the seventh planet from the Sun and the third largest (by diameter). Uranus, the first planet discovered in modern times, was discovered by William Herschel while systematically searching the sky with his telescope on March 13, 1781.

Uranus is composed primarily of rock and various ices, with only about 15% hydrogen and a little helium (in contrast to Jupiter and Saturn which are mostly hydrogen). Uranus' atmosphere is about 83% hydrogen,15% helium and 2% methane. Uranus' blue color is the result of absorption of red light by methane in the upper atmosphere.

Uranus is a large, plain, blue-green planet which can only be seen from the Earth with the unaided eye on a clear, dark night. Uranus has 15 satellites orbiting in nearly circular orbits in the planet's equatorial plane, hence they are also "tilted" about 90 to the ecliptic.

Uranus' core is in many ways similar to the cores of Jupiter and Saturn minus the massive liquid metallic hydrogen surrounding the cores. Uranus's diameter is four times larger than Earth's and its mass is 14. Uranus is best remembered as the "tilted planet," or the "planet that rotates on its side," because of the inclination of its rotation axis with respect to its orbital plane.

Rings

The rings of Uranus were discovered from ground-based observations in 1977. Rings of Uranus has a faint planetary ring system, composed of dark particulate matter up to ten meters in diameter. There are 11 known rings, all very faint; the brightest is known as the Epsilon ring. This was of considerable importance since we now know that rings are a common feature of planets, not a peculiarity of Saturn alone. These rings are very dark and narrow, unlike Saturn's, which are bright. Uranus has 21 known natural satellites (and may have at least 27), both within the rings and outside of the rings.

Orbit

Orbit around the Sun: Uranus goes around the Sun once every 84 Earth years. Most have nearly circular orbits in the plane of Uranus' equator (and hence at a large angle to the plane of the ecliptic); the outer 4 are much more elliptical.

Uranus is nevertheless hotter at its equator than at its poles. Uranus is no longer the bland boring planet that Voyager saw. Uranus is unique in our solar system because it is tilted 98 degrees. Uranus is the farthest planet that can be seen without a telescope. Uranus has a mass (quantity of matter) 14 1/2 times larger than that of Earth. Uranus seems to radiate as much heat into space as it gets from the sun. Uranus is composed mostly of liquid water, methane and ammonia, surrounded by a thick gas atmosphere of mostly hydrogen and helium. Uranus, like Venus, has a rotation axis that is greatly tilted and sometimes points near the Sun. Uranus is composed mostly of rock and ices, but with a thick hydrogen and helium atmosphere.

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