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Jovian planets are also known as gas giants. There are four Jovian planets: Jupiter, Saturn, Uranus, and Neptune. These four planets also comprise the outer planets. The term Jovian came from Jupiter, describing the other gas giants in our Solar System as Jupiter-like. Despite common belief, gas giants are not composed entirely of gas. A rocky core exists somewhere within these balls of gas, but it is difficult if not impossible as of yet, to determine where this center is. Because of the intense high temperatures in the middle of these planets, the rocky core of a gas giant is actually believed to be liquid heavy compounds, such as nickel. Thus, it is sometimes misleading when astronomers refer to the rocky core of these planets. The Jovian planets are larger than the other planets of the Solar System and have dozens of moons.
Jupiter, the largest planet in the Solar System, is bright and can be viewed by the naked eye from Earth. In addition to being the largest, Jupiter has the greatest mass of all the planets. The planet has 63 moons, more than any other planet in the Solar System. Jupiter has rings, like all of the Jovian planets, although they are very faint. It is often considered the prototype of gas giants.
Saturn is the 2nd largest planet in the Solar System with distinctive, highly visible rings. Saturn has the biggest and most visible rings of any planet in the Solar System. Records indicate that Galileo first discovered the planet’s rings through his telescope. Sixty-one moons of Saturn have been identified as of 2009, although astronomers have only named 52 of them.
William Herschel discovered that Uranus was a planet in 1781. Although astronomers had identified it earlier, it was mistaken for a star because it is a dim planet with a slow orbit. Helium and hydrogen are the main components of the atmospheres of all the gas giants, but Uranus and Neptune contain higher amounts of methane and ammonia. The higher amount of ices in the atmospheres of these planets results in the Neptune and Uranus being nicknamed the ice giants. One unique feature of Uranus is its axial tilt. The planet rotates on its side with a tilt of 97.77 degrees.
Higher levels of methane and ammonia make Neptune the other ice giant in the Solar System. The high levels of ammonia in Neptune’s atmosphere are partly responsible for the planet’s bright blue color. Neptune also has a difficult to see planetary ring, which could not be confirmed until Voyager’s mission in 1989.
Check out these other articles from Universe Today on the outer solar system and the inner solar system.
Astronomy Cast has a number of episodes on the Jovian planets including this one on Jupiter.