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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The Rings of Saturn

All the Gas giants of our Solar System have rings, but the ones around Jupiter, Uranus and Neptune are relatively small. Saturn's rings are magnificent.

Discovery

The first reference to Saturn's rings appears to be from Galileo. In 1610 he looked at Saturn through his telescope. He was puzzled by what he saw. He described the rings variously as ears, handles and arms. He said that the planet appeared to be triple-bodied. He also speculated that Saturn might have two large moons.

His telescope was not very powerful, and he was hampered in his observations by the fact that the angle the rings are seen from, looking from the Earth, changes. It we are looking at the rings when they are completely edge on, they are difficult to see at all.

In 1659, Christiaan Huygens looked at the rings with a more powerful telescope and saw that they are flat rings round the planet.

Flat Rings

The rings are very big in the sense that they look big, looking at them flat. The closest ring is something like 7000 Kilometres from the Planet while the edge of the furthest one may be about 250,000 Kilometres from Saturn's surface. However, many of the rings seem to be only about 10 Metres thick.

Mass

The total amount of matter in the rings may only be about the same as a small moon, perhaps one with a diameter of 400 Kilometres although different measurements and their interpretations give quite different answers.

Water

The main material in the rings appears to be water ice.

Age

This is another thing we do not know. Different theories about the rings give ages of between 100 million and 4 billion years.

Life in the Rings

This might sound like a strange idea, and probably few serious scientists would think it is likely, but we really do not know how widespread life is in the universe, or what forms it can take. Ben Bova introduced the idea of life in the rings of Saturn.

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Jupiter - A Closer Look

Jupiter is the fifth planet from the sun and is by far the largest in the solar system. In fact, Jupiter is so massive that it's 2.5 times the size of the all the planets combined. Along with Saturn, Uranus, and Neptune, Jupiter is classified as a gas giant.

The existence of the planet has been known to astronomers for centuries. Next to the moon and Venus, Jupiter is the brightest object in the sky. Note that on occasion, Mars can exceed it's brightness.

The most notable characteristic of the planet is it's Great Red Spot. This Great Red Spot is a giant storm that has been known to exist since the 17th century. Although Saturn is easily identified by its rings, many people aren't aware that Jupiter has a faint planetary ring system. The planet has at least 63 moons, one of which is larger than the planet Mercury.

Mass

Jupiter dwarfs any other celestial body in our solar system other than the sun. It's size is a bit baffling but some refer to Jupiter as a "failed star". Although this has not been proven scientifically, this notion is generally accepted. The smallest red dwarf star is still 30% larger than Jupiter.

Jupiter's Moons

As mentioned earlier, Jupiter has at least 63 moons. These moons are so massive they are easily the largest satellites in the solar system. Io, Europa, and Ganymede are among the largest of this group. These 3 moons have an intriguing orbit around Jupiter. For every 4 orbits that Io makes, Europa makes exactly 2, and Ganymede completes 1. This pattern is known as a Laplace resonance.

Galileo discovered Jupiter's 4 largest moons, Io, Europa, Callisto, and Ganymede, using a telescope in 1610. This is believed to be the first observation of moons other than Earth's. This Galilean credit comes not without dispute. Gan De, a Chinese astronomer, is believed to have discovered the moons in 362 BC according to a Chinese astronomy historian named Xi Zezong.

Orbit and Rotation Specs

Jupiter's average distance from the sun is 778 million km. That is 5 times the distance between the Earth and the Sun. Unlike the Earth, Jupiter has a small axial tilt resulting in it having no seasonal real changes. Jupiter has the fastest rotation of all the planets in the Solar System. It rotates in a mind-numbing 10 hours. This excessive rotation causes a very noticeable bulge that can be seen with an entry-level telescope.

Is There Life?

Jupiter's extreme environment does not leave much room for the possibility of sustainable life. It possesses some basic building blocks of life that could form organic compounds but Jupiter's chances end there at least in the terms of Earth-like life.

Jupiter is much more than just the largest planet in our solar system. It has fascinated astronomers and casual star gazers for millenniums and will continue to do so. The more we learn about our neighboring planets may give us an idea of what other planets are like outside of our solar system.

Every budding astronomer should experience the majestic nighttime skies with the best star gazing equipment available. BinocularsAnnex.com has a vast array of reflecting telescopes, refracting telescopes, and dobsonian telescopes to fit your liking.

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Some Cool Facts About the Planet Mars, By David J R

Here are some facts about our neighboring planet i.e. Mars. I am sure you will enjoy reading these. So, here they are...

A day on Mars is just about 39 minutes longer than that of Earth. This means that it spends about 39 minutes more than Earth to revolve around itself. While a Martian year consists of 686.98 Earth days.

Normally the temperature on this planet remains between -140° C to 20° C

Do you have any idea about age of the red planet. Can you guess? In case you can't, it was formed about 4.5 billion years ago.

It is 6794.4 km in diameter.

The atmosphere of this planet is mostly made up of Carbon Dioxide, which according to an estimate is 95.32% of the total atmospheric composition. Nitrogen is the second largest content which makes the 2.7% of the atmosphere.

It is thought that the core of this planet is composed of iron, nickel, and sulfur.

It has seasons like Earth. This scenario is caused by the tilt of the planet's axis, at a similar angle to the tilt of Earth's axis.

A person who weighs 70 pounds on Earth would weigh 27 pounds on Mars.

The red planet was named after the Roman god of war.

It has polar caps like Earth, containing frozen different layers of carbon dioxide, small amount of water and dust.

The average temperature on the planet Mars is -55 C or -67 F.

Did you know that the third month March is named after Mars, which is not the planet Mars but the god.

Did you know that the red planet has the largest canyon in the solar system? It would reach from Los Angeles to Chicago if it was on Earth!

It is 227,900,000 km away from the Sun.

The mean density of the red planet is 3933kg/m3, while that of the Earth is 5515kg/m3. So, it's density is about 30% less than that of the Earth.

It has almost no atmosphere. The air pressure at the surface of Mars is only 1% of what we have here on Earth.

This planet can be seen from the Earth with a naked eye.

The average distance of Mars from the Sun is almost 228 million kilometers.

Scientists believe that 3.5 billion years ago, Mars experienced the largest known floods in the solar system.

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Our Life-Friendly Planet Earth - Are We One and Only?

Total Solar Eclipse - Window to the Universe

In addition to the dramatic and awe-inspiring novelty of a total solar eclipse, the highly improbable exact size/distance equality between sun and moon as viewed from Earth, provides a unique opportunity for modern and advanced telescopy to observe the heavens as never before. The perfect match of relative sizes in a total eclipse completely blocks out the sun's aura, thus, for brief moments, mankind has lately been able to clearly see the universe without the blocking aura of the sun, and therefore is better able to probe heaven's mysteries.

What has been learned is, not only that Earth and our moon seem to be the best viewing platform in all of space, but also that Earth is quite possibly the only life-sustaining planet in the universe - despite the billions of stars in millions of galaxies. This seems to be so because of many factors:

• Earth's encompassing magnetic field from its molten-metal core plus the four giant planets patrolling outer orbits (Jupiter, Saturn, Uranus, Neptune) provide powerful protective shielding against deadly cosmic radiation - devastating to star systems in the very common spiral galaxies such as our Milky Way.
• Black hole singularities, one at the core of our Milky Way, are deadly, deeply mysterious structures of "infinite" density. Their gravity fields are so powerful that even rays of light cannot escape.
• the fragility of our water-based life in an extremely hostile universe.
• our optimum distance from the sun provides a life-friendly moderate temperature range. varying between tolerable heat and tolerable cold.
• As evidenced in a recent NASA (Phoenix) soil experiment on Mars, foreign substances in soils or atmospheres may be inhospitable to fragile life systems such as ours - Mars soil, for example is extremely oxidizing and destructive.
• Despite almost fifty years of effort, and with increased sophistication of radio receivers and telescopes (estimated at 100 trillion times more powerful than the first attempt to contact extra-terrestrial life in 1960), there has been no success whatsoever. The program is called SETI - Search for Extra-Terrestrial Intelligence.
• Even if other life does exist elsewhere in the Universe, the unimaginable distances plus the (Einstein established) fact that the speed of light cannot be exceeded, preclude any form of communication, much less interaction (as in the popular Television series Star Trek.)

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Venus, A Mysterious Planet

Although it's our closest neighbor, we haven't known much about Venus until recently. Ancient civilizations however, were keeping track of it long ago. Each one had unique beliefs.

A planet with many names, we know it as Venus, the Roman goddess of love and beauty. The Greeks believed that it was two separate entities. Hesperus when they saw it in the morning, Phosphorus when they saw it in the evening. Mayans thought Venus was the god Kukulkan. Aztecs believed it was Quetzalcoatl. You have to admire them for the interesting explanations they came up with to describe this entity in their night sky!

Venus is an inner planet, the second from the sun. It's also the second brightest object in the night sky after the moon. Although you can observe it without any aids, even with a telescope you can't see very much as it is covered in thick clouds, which reflect light back. The only way to see past the clouds is with a radar system.

In some ways Venus is similar to Earth in that they are almost the same size, have almost the almost the same density and gravity. They both have thick atmospheres made of gases. However it does not have a moon, rings, or a magnetic field. Venus has a similar composition to the Earth as well.

Astronomers and scientists were curious to know what was beneath the clouds. Two spacecraft went up on the space shuttle Atlantis to find more about the surface, clouds, and other data. In May of 1989 on the STS-30 mission, Magellan went up to orbit around Venus. Galileo followed on the STS-34 mission in October of 1989. Although Galileo's main objective was to probe Jupiter, it did a flyby of Venus to take infrared pictures of the clouds in February of 1990. Magellan was named after the 16th century explorer Ferdinand Magellan. Even though Magellan was launched first it did not go into orbit around Venus until August of 1990. Magellan mapped the surface using a SAR, Synthetic Aperture Radar.

From these and other probes and spacecraft we have learned a number of things. The surface is dusty, arid, and mostly flat with some deep valleys. It is very hot, with a surface temperature of 860°. This makes Venus the hottest planet in the solar system! Since the atmosphere is made of mostly carbon dioxide, Venus is uninhabitable. The barometric pressure is almost 100 times that of the Earth. To give you an idea of how much that is, the probes that landed on the surface would fail because of the high pressure. It sometimes rains on Venus, sulfuric acid and water vapor. Because of the high temperatures and dense cloud cover, Venus has what some scientists call "the greenhouse effect gone wild". What that means is heat from the sun can get in, but cannot escape. Put very simply, the clouds hold all the heat in.

We have learned a lot about Venus in the last few centuries. We still watch in the evening or in the morning depending on what phase it is in. But somehow it still seems mysterious the way it hides behind its clouds.

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Mercury- Messenger of the Gods, By Michael D. Watson

In our tour of the solar system, we should begin by exploring the innermost planet. A short distance from the inferno of our sun we find it, hurtling through space at 40 to 60 kilometers per second in its 88 day cycle around the sun. As we approach it we notice its similarity to a body much closer to Earth, our own moon. It too is heavily cratered, with no atmosphere (or only a trace of one) to protect its surface or erode signs of previous collisions. The sun as seen from this distance is approximately three times as large as from Earth, and we know this is going to be the most dominant force affecting our trip to this planet.

Now we have touched down and we take a quick look around. We know that the surface gravity of Mercury is 38% of Earth's, so if we weighed 200 pounds before, here we weigh only 76 pounds. Looking up at the sky we see a black, star-speckled sky dominated by the fiery globe of a sun almost three times larger than we are familiar with. There is only the faintest trace of an atmosphere, and the only way we even know it is there is the instrumentation we have with us. It will be totally useless to us. The sun beats down unabated in all its fury, and the temperature hovers around 800 degrees Fahrenheit. If we were on the night side the temperature would drop to -270 degrees. We would never survive here without space suits.

Bending down to inspect the surface we find a layer of dust similar to what astronauts found on the moon. This is the result of billions of years of meteor impacts, and also the extreme temperature differentials applied from a hellishly close sun. The processes which shaped this world across the eons were much different than the ones which shaped our home planet.

Around us are the pockmarks of craters, some mountain ranges, and a horizon much nearer than what we know at home.

Contrary to what astronomers once thought, there is actually a cycle of days here, but it is much different than anything we are used to. Mercury is not tidally locked with the sun, but tidal forces have slowed it to the point where its day is 58 of our days (indeed it will one day many years from now become locked one side to its huge neighbor). This means that Mercury's day is about three quarters as long as its year. This results in some very peculiar observations if we were to stay that long. We would observe the sun snake across the sky very slowly. In certain places on this world we would then see the sun slow and actually backtrack a short distance before continuing its slow march across the sky. Then the very long night would follow.

We take one more look around this world. No, Mercury is not an enticing place for humans to visit. Maybe one day we will have reason to be here, either for the rich deposits of iron and other metals or for observational purposes, but this is not the day.

Studies of Mercury Through History
Mercury has been know and observed at least since the times of the Sumerians in the 3rd millennium BC. Following the Sumerians there is better documentation from the Babylonian Empire. Records from the 7th century BC refer back to much earlier records which described observations of the planet. The Babylonians called the planet Nebu, after the messenger of the gods in their mythology. This is an interesting parallel to the later Greek mythology and reference to the innermost planet. The ancient Greeks had two names for the planet, Apollo visible in the morning and Hermes visible in the evening. They eventually came to understand that these were the same object, and it was even proposed this early in history that Mercury and Venus orbited the sun.

Early modern astronomy began making observations of Mercury in the early 17th century when Galileo turned an early telescope to the inner world. A sketchy vision of the planet developed from that point, but its proximity to the sun has always made this one of the most difficult members of our solar system to study. It has only been recently with the advent of new imaging techniques that ground-based observation has drastically improved.

And what of research with space probes? This is also laced with technical difficulties. An application of Newton's Laws of Motion shows that it takes more rocket fuel to achieve an orbit around Mercury than it takes to escape the solar system. Because of this only one spacecraft has visited the planet to date, the Mariner 10.

The Mariner 10 was launched on November 3, 1973 to study both Venus and Mercury. After its study of Venus, the probe made three flybys of Mercury in 1974 and 1975 when it mapped about 45% of the planet's surface. Its closest approach was 203 miles on March 16,1975. The Mariner 10 circles the sun in its own lone orbit around the sun to this day, although its electronic instruments have long since been destroyed by the sun's intense radiation.

Our most ambitious Mercury research project to date was begun August 3,2004 with the launch of the Messenger by NASA from Cape Canaveral. After two quick flybys of Venus in 2006 and 2007 the Messenger will finally work its way inward and make three flybys of Mercury in 2008 and 2009. Then in March of 2011, if all goes well, it will finally become the first orbiting spacecraft around Mercury. It is carrying high resolution imaging devices, spectrometers to determine the composition of the crust, and magnetometers to study charged particles around the planet.

There is an astronomical event which is of interest to amateurs and professionals alike, but not necessarily for any scientific value. Once every couple of centuries there is an occultation of Mercury and Venus. This occurs when Venus actually passes directly in front of Mercury for a few minutes. The last one occurred on May 28,1737 and the next will occur in 2133.

Structure of Mercury
Much of Mercury's mass is composed of an iron rich core. Current theories suggest that this core comprises most of the 4879 mile diameter of the planet. This is surrounded by a 350-400 mile thick mantle and finally by a crust some 100 miles thick. Because of Mercury's slow rotation period, there is very little tectonic or volcanic activity.

There have been several theories presented to explain why Mercury is so metal rich, and why its core comprises such a huge part of the planet's structure. One popular theory is that the planet was struck by a large body early in its history and lost most of its outer, "lighter", mantle. Another theory is that the extreme heat of the early sun vaporized the outer part of the planet, giving the young Mercury a dense atmosphere of gaseous rock, which was carried away by the huge solar winds of a much more volatile sun. The competing theories to explain the unusually heavy composition of Mercury will be tested by the upcoming Messenger mission.

The Future of Mercury and Its Possible Role in Our Own Future
Mercury's most dominant feature makes it an attractive part of our future: its huge stores of heavy metals, especially iron. Although its proximity to the sun makes it hard to imagine humans working and living there, I can envision automated factories mining its surface and freighters picking up the ore to bring it back for our use.

Mercury will remain pretty much as it is for billions of years to come. As the sun slowly gains in intensity over the next 4 to 5 billion years, the planet's surface temperature will slowly rise with it. Then a singular moment will arrive as the entire solar system changes with the beginning of the sun's passage into its next phase. When the sun consumes a critical amount of its hydrogen fuel it will, within a matter of just a few days, enter its red giant phase.

At that time Mercury will be the first of the inner planets to be entirely consumed.

Planetary Statistics of Mercury
1. Closest distance to the sun(perihelion).....46,001,272km(28,583,865 miles)
2. Farthest distance from the sun (aphelion).....69,817,079km(43,382,322 miles)
3. Density.....5.427 g/cubic cm
4. Diameter.....4879.4km (3031.9 miles)
5. Orbital period (year).....87.96934 days
6. Rotation period (day).....58.6462 days
7. Max surface temperature.....700K (800F)
8. Satellites.....None
9. Atmospheric pressure.....trace
10.Surface gravity.....38% Earth's

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Solar System Basics

Our Sun and eight planets with their moons make up what astronomers call the "Solar System". Although our Solar System is not the only one in the galaxy, scientists have not yet found the one like it. Each planet in the Solar System is as unique as the system in which it orbits. As a matter of fact, eight planets have very few attributes in common. They similarly orbit around the Sun, and they have largely the same chemical compositions. Beyond those two properties, the planets contrast far more sharply than they neatly compare.

The Sun's gravity and magnetic field, called the "heliosphere", envelop the major planets and all the dwarf planets in the Solar System. Although we frequently represent the planets' orbits as circular, the major planets actually trace cosmic ellipses as they rotate around the Sun.

The planets take their names from Roman gods and goddesses. Of course, "Jupiter", by far the largest of the eight planets, is named for the King of the Roman gods. Saturn, frigid and ice-bound almost beyond measure and imagination, paradoxically carries the name of the Roman god of agriculture. Mars, relatively small and desolate, carries the name of the Romans' war god.

Until 1977 scientists thought only Saturn had "rings" - vast planes of ice and rocks suspended in orbit around them. Further investigation has shown that Uranus and Neptune also have ring systems. Naturally, their ring systems are not so pronounced as Saturn's, because they are proportional to the two much smaller planets.

Astronomers refer to the bodies we generally call "moons" as "satellites", and our moon has generally the same characteristics and properties as the other 139 satellites in the Solar System: it orbits the Earth as the Earth orbits the Sun, held in its elliptical pattern around the third planet by gravity and magnetism much like the Sun holds the planets.

In the last several years debate has raged over Pluto's status: does it qualify as a planet, or does it fall into some other category of celestial objects?

In the course of the debate over Pluto the International Astronomical Society (IAS) the governing body that sets standards for measurements, observations, and discoveries changed the definition of and criteria for a planet. In order to meet official planet standards, a celestial body must orbit the Sun, have sufficient gravity to maintain a uniformly spherical shape, and clear its own orbit. After the IAS established its current standards, Pluto no longer met the requirements. Astronomers, after changing their assessments several times, finally classified Pluto as a "dwarf planet".

Pluto travels in a little cluster of celestial objects very much like it, and astronomers developed an official classification for the whole group, calling these objects "plutoids". They have gravity and hold their shape as they orbit the Sun, but they have not cleared their orbits. Many astronomers have become fascinated with the plutoids, arguing that insight into their development and evolution will contribute to proving "The Big Bang Theory".

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