Outer Planets
Astronomers have divided the eight planets of our solar system in to the
inner planets and the outer planets. The 4 inner planets are the closest to
the Sun, and the outer planets are the other four – Jupiter, Saturn, Uranus,
and Neptune. The outer planets are also called the Jovian planets or gas
giants. Like the inner planets, the outer planets have similar characteristics
to one another. The outer planets are so much larger than the inner planets
that they make up 99 percent of the mass of the celestial bodies that orbit
the Sun. Although mainly composed of gas, the outer planets also have
other ingredients. Somewhere at the center is what scientist refer to as a
rocky core, although it is actually composed of liquid heavy metals. While
the inner planets have few or no moons, the outer planets have dozens
each. The inner and outer planets are separated by the asteroid belt.
Jupiter is the largest planet in our Solar System with a mass more than
three hundred times Earth’s mass. Jupiter is not only the largest planet; it
also has the most moons – 63 identified so far. Jupiter is one of the
brightest objects in the sky and has a very stormy atmosphere. One major
storm, the Great Red Spot, is as big as the Earth.
Saturn is hard to miss with its distinctive, large rings. Although all of the
outer planets have rings, Saturn’s are the most visible ones. Astronomers
did not know there were any other planets with rings until 1977 when
Uranus’ rings were discovered. Soon after that, astronomers discovered
rings around both Jupiter and Neptune.
Uranus has the smallest mass of the outer planets, although in size it’s a
little bigger than Neptune. It is the only planet to rotate on its side.
Scientists are unsure why it rotates that way, although there are a couple
theories. One suggests it suffered a major collision and another
hypothesizes that smaller shifts during the planets’ formation caused its
unusual rotation.
Neptune is the final outer planet in the solar system. Neptune’s winds are
the fastest of any planets in the Solar System and can reach more than
1,200 miles per hour. While all of the outer planets’ atmospheres contain
hydrogen and helium, Neptune and Uranus contain significant amounts of
what astronomers call ices. These ices include water, ammonia, and
methane. The methane in Neptune and Uranus is what gives the planets
their blue color.
