Solar System Overview
The
4 Terrestrial Planets
The four small inner planets closest to the Sun--Mercury, Venus, Earth, and Mars--are called the terrestrial planets because they have solid rocky surfaces.
The 4 Jovian Planets
The
four large outer planets beyond the orbit of Mars-- Jupiter, Saturn, Uranus,
and Neptune--are called gas giants because they are composed primarily of
two gases, hydrogen and helium.
Pluto (and Charon)
Beyond
the gas giants is one tiny little distant planet called Pluto (after Pluto
the Roman god of the deep dark underworld because Pluto is
way out there in the deep dark outerworld of our Solar System).
Pluto has a solid rocky surface (like the terrestrials) but, being so far
away from the Sun, has a much colder surface than the terrestrial planets.
Atmosphere
Nearly every planet--and even some of their moons--has an atmosphere, even though it may be so small that it’s close to none at all. What is an atmosphere? Good question. An atmosphere is the gas blanket that surrounds a planet. It can be thick or thin. An atmosphere is composed of different types of gases all at different concentrations.
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For example, Earth’s atmospheric gases are primarily nitrogen (79%) and oxygen (21%). Venus, Earth’s closest neighbor (after the Moon of course), has a dense atmosphere of carbon dioxide, with traces of poisonous sulfur dioxide. Mars, on the far side of Earth (away from the Sun), has an atmosphere of carbon dioxide that is extremely thin and almost not there.
The four Jovian gas giants are primarily gas like our sun. But, even they have a type of atmosphere surrounding their outer limits.
Pluto which is way out there at the edge of our Solar System is quite special. It has an atmosphere only half the year. You see, when Pluto travels to the outer regions of its orbit, the atmosphere freezes and falls like snow to the planet's surface.
These are just a few of the
wild and natural wonders of our celestial neighbors.
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