Our Solar System,

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Our Solar System, Part II
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Terrestrial or Rocky Planets
Mercury, Venus, Earth, Mars
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Mercury
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• Mercury
• Average distance from Sun 57,910,000 kilometers
  (35,980,000 miles)
• Diameter 4,880 km (3,032 miles)
• Mercury is, in many ways, similar to Earths
  moon, because its solid surface is covered with
  craters.
• There is evidence of water ice in the protected
  shadows of craters near the north pole.
• Mercury has almost no atmosphere.
• Mercury is the smallest planet and the closest
  to the Sun.
• Mercurys diameter is about one-third of Earths
  diameter.
• Mercury has no moons.

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MESSENGER
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Venus
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• Venus
• Average distance from Sun 108,200,000
  kilometers (67,230,000 miles)
• Diameter 12,103 kilometers (7,521 miles)
• Venus is the sixth largest planet and the second
  from the Sun.
• The surface is rocky and very hot. The
  atmosphere completely hides the surface and traps
  the heat. The temperature is around 482 degrees
  Celsius (900 degrees Fahrenheit). The atmosphere
  contains mostly carbon dioxide. The layers of
  clouds surrounding Venus contain sulfuric acid.
• Venus looks white and featureless because of the
  dense clouds that surround it.
• Venus is sometimes regarded as Earths sister
  planet. The two objects are very similar in size,
  mass, density, and volume. The two planets also
  are made from similar kinds of material, such as
  rock.
• However, Venus is very different from Earth. It
  has no oceans, its day is longer than its year,
  and it has no moons.

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The surface of Venus is always covered by a veil
of thick clouds and remains hidden from even the
powerful telescopic eyes of earth-bound
astronomers. But in the early 1990s, using
imaging radar, the Venus orbiting Magellan
spacecraft was able to lift the veil from the
face of Venus and produce spectacular high
resolution images of the planet's surface.
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Earth
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• Earth
• Average distance from Sun 149,600,000
  kilometers (92,960,000 miles)
• Diameter 12,756 kilometers (7,926 miles)
• Earth is the fifth largest planet and the third
  from the Sun.
• Earths atmosphere is made of 78 percent
  nitrogen and 21 percent oxygen, with traces of
  argon, carbon dioxide, and water.
• Liquid water covers 71 percent of the Earths
  surface. The other 29 percent is made of rock and
  soil.
• White clouds of water droplets and ice crystals
  hide much of Earths surface.
• Earth has one Moon.

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Mars
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• Mars
• Average distance from Sun 227,940,000
  kilometers (141,600,000 miles)
• Diameter 6,794 kilometers (4,222 miles)
• Mars surface has craters, valleys, ridges,
  hills, and plateaus.
• A long time ago, Mars surface had liquid water,
  too. The planet has clear evidence of erosion in
  many places.
• Mars has a very thin atmosphere that contains
  mostly carbon dioxide.
• Mars surface is red its clouds and haze look
  blue. Mars is the seventh largest planet and the
  fourth from the Sun. Its diameter is about
  one-half of Earths diameter.
• Mars has two known moons named Phobos and
  Deimos.

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Husband Hill on Mars as taken from the Spirit
Rover
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Volcanic activity on Mars has produced towering
mountains. The largest one, Olympus Mons, is
pictured here in this Viking Orbiter image.
Olympus Mons is a shield volcano nearly 15 miles
high and over 300 miles wide at its base. By
comparison, Earth's largest volcano, Mauna Loa in
Hawaii, is just over 5 miles high and about 12
miles wide.
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Asteroids
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• Asteroids
• Scientists estimate that there are one million
  asteroids bigger than 1 km (0.6 miles) across. A
  tiny fraction of these have been found. There are
  likely hundreds of thousands more that are too
  small to be seen from Earth.
• Asteroids are bodies of rock, metal ore, and
  some ice. They are covered with craters.
• One of the largest is called Vesta. Vesta is
  different from most asteroids. Data collected by
  the Hubble Space Telescope have shown that Vesta
  has light and dark areas on its surface.
• Most asteroids orbit the Sun in the area between
  Mars and Jupiter called the asteroid belt.
• Though they are not visible with the naked eye,
  many asteroids can be seen with small telescopes,
  appearing as small points of light.

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Gas Giant Planets
Jupiter, Saturn, Uranus, Neptune
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Jupiter
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• Jupiter
• Average distance from Sun 778,330,000
  kilometers (483,600,000 miles)
• Diameter 142,984 kilometers (88,850 miles)
• Jupiter is the largest planet and the fifth
  planet from the Sun. Its diameter is about 11
  times greater than Earths diameter.
• More than 1000 Earths could fit inside Jupiter.
• Jupiter does not have a solid surface. The
  planet is a ball of liquid surrounded by gas.
• By mass, Jupiter is made of 75 percent hydrogen
  and 23 percent helium, with traces of methane,
  water, ammonia, and, in its core, some rock.
• Jupiter has an interesting feature called the
  Great Red Spot, a huge storm of swirling gas that
  has lasted for hundreds of years.
• Jupiter has more than 60 moons. Its four largest
  moons were discovered in 1609 by Galileo.

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From July 16 through July 22, 1994, pieces of an
object designated as Comet Shoemaker-Levy
collided with Jupiter. This is the first
collision of two solar system bodies ever to be
observed, and the effects of the comet impacts on
Jupiter's atmosphere have been simply spectacular
and beyond expectations. Comet Shoemaker-Levy 9
consisted of at least 21 discernable fragments
with diameters estimated at up to 2 kilometers.
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Saturn
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Cassini
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• Saturn
• Average distance from Sun 1,429,400,000
  kilometers (888,200,000 miles)
• Diameter 120,536 kilometers (74,900 miles)
• Saturn is the second largest planet and the
  sixth from the Sun.
• Its diameter is about nine times larger than
  Earths diameter.
• Saturn is made of materials that combined to
  make it lighter than water. If you could fit
  Saturn in a bathtub, it would float! By mass,
  Saturn contains about 92 percent hydrogen and 6
  percent helium, with traces of methane, ammonia,
  water, and rock.
• Saturn has thousands of rings. Saturns rings
  are made of rocks, dust, and water ice, all of
  which are orbiting the planet.
• Saturn has more than 30 moons. Titan, Saturns
  largest moon, is the only moon in the solar
  system with a significant atmosphere.

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Saturnian Moon Mysteries The Anomalies of
Hyperion Iapetus
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Hyperion
What lies at the bottom of Hyperion's strange
craters? Nobody knows. To help find out, the
robot Cassini spacecraft orbiting Saturn swooped
past the sponge-textured moon in late 2005 and
took an image of unprecedented detail. That
image, shown above in false color, shows a
remarkable world strewn with strange craters and
a generally odd surface. The slight differences
in color likely show differences in surface
composition. At the bottom of most craters lies
some type of unknown dark material. Inspection of
the image shows bright features indicating that
the dark material might be only tens of meters
thick in some places. Hyperion is about 250
kilometers across, rotates chaotically, and has a
density so low that it might house a vast system
of caverns inside.
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Iapetus
What has happened to Saturn's moon Iapetus? A
strange ridge 12 miles high and 12 miles wide,
crosses the moon near the equator, making Iapetus
appear similar to the pit of a peach. Half of
Iapetus is so dark that it can nearly disappear
when viewed from Earth. Recent observations show
that the degree of darkness of the terrain is
strangely uniform, like a dark coating was
somehow recently applied to an ancient and highly
cratered surface. The other half of Iapetus is
relatively bright but oddly covered with long and
thin streaks of dark. A 400-kilometer wide impact
basin is delineated by deep scarps that drop
sharply to the crater floor. This image was taken
by the Saturn-orbiting Cassini spacecraft during
a flyby of Iapetus.
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Uranus
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• Uranus
• Average distance from Sun 2,870,990,000
  kilometers (1,784,000,000 miles)
• Diameter 51,118 kilometers (31,760 miles)
• Uranus is the third largest planet and the
  seventh from the Sun. Its diameter is about four
  times larger than Earths diameter.
• Uranus is one of the four giant gas planets.
  Like other giant gas planets, Uranus core is
  made from rock pieces and frozen gas.
• The atmosphere on Uranus contains, by mass,
  about 72 percent hydrogen, 26 percent helium, and
  some methane. The methane is what makes the
  planet appear blue-green.
• Uranus spins on an axis that is tilted more than
  any other planet. The planet looks like its
  spinning on its side.
• Uranus has more than 20 moons. William Herschel
  discovered its two largest moons, Titania and
  Oberon, in 1787.

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Neptune
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• Neptune
• Average distance from Sun 4,504,000,000
  kilometers (2,799,000,000 miles)
• Diameter 49,528 kilometers (30,780 miles)
• Neptune is the fourth largest planet and the
  eighth from the Sun.
• Neptune is about 30 times as far from the sun as
  Earth. Its diameter is about four times larger
  than Earths diameter.
• Neptunes atmosphere contains mostly hydrogen
  and helium, with a small amount of methane. The
  methane gives Neptune its blue-green color.
• Neptune has strong winds that sometimes gust to
  1,400 kilometers per hour (900 miles per hour).
• Neptune has more than ten moons. The largest,
  Triton, is almost as big as Earths Moon.

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Dwarf Planets
A "dwarf planet" is a celestial body that (a) is
in orbit around the Sun, (b) has a nearly round
shape, (c) has not cleared the neighborhood
around its orbit, and (d) is not a satellite.
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Comets
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Kuiper Belt The Kuiper Belt is a region in our
outer solar system where many "short-period"
comets originate. The orbits of short-period
comets are less than 200 years. This region
begins near Neptunes orbit at 30 astronomical
units (AU) and extends to about 50 AU away from
the Sun. An astronomical unit is the average
distance between Earth and the Sun. The Kuiper
Belt may have as many as 100 million comets.
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Our Solar system is surrounded by two large
formations of objects. The Kuiper Belt The
Oort Cloud
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