The Solar
System
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Our
solar system has one star, called the Sun, eight planets, moons, comets, asteroids, and meteoroids.
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As
of May 2007 there are 206 planets in 97 solar systems. Less than 10 years
earlier there were only 9 known planets.
Rocky Planets
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The four planets closest to
the Sun are called rocky planets because they are composed of dense,
rocky material.
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Mercury is closest to the Sun and has no atmosphere due to a weak gravitational
force.
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Venus is second from the Sun and is covered with a cloud of sulfuric acid.
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Earth is third from the Sun and the only planet where water exists in all
three phases (solid, liquid, gas).
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Mars, also called the ÒRed PlanetÓ, is fourth from the Sun and has all of the
elements necessary for colonization.
Gaseous Giants
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The four planets outermost
from the Sun are called gaseous giants because they are composed of
gasses and icy materials.
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Jupiter is fifth from the Sun and the largest planet.
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Saturn is sixth from the Sun and has rings.
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The two outermost planets,
which we know little about, are Uranus and Neptune.
Comets
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A comet is a large
chunk of ice, gas, and dust (dirty snowball) traveling through space.
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Comets originate from a
cluster of debris from beyond the planets called an Oort
cloud.
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Comets follow a path that
revolves around the Sun
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Comets - Schedule
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Comet Halley orbits every 76 years
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HalleyÕs last appearance was in 1987
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Comet Hale-Bopp orbits every 3,000 years
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Hale-BoppÕs last appearance was in 1997
Asteroids
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An asteroid is a
small rocky object.
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Most asteroids are found in
an asteroid belt between Mars and Jupiter.
Meteors
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A meteor is an
asteroid that has entered EarthÕs atmosphere.
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A Òshooting starÓ is
actually a meteor.
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It is called a meteorite
if it survives to strike EarthÕs surface.
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The extinction of dinosaurs
is blamed on a meteorite crashing into the Earth and causing a dust cloud to
block out sunlight for many years.