Which Planets Have Surfaces Made of Gases?

Jupiter

• Jupiter is the largest and most massive planet in the solar system. This gas planet is roughly 11 times the diameter of the Earth, and 300 times as massive. Jupiter's composition resembles that of a star; in fact, if the planet had more mass, it would have become a sister-star to the sun. It consists primarily of light elements, including 90 percent hydrogen, 10 percent helium and trace amounts of methane. Beneath its surface clouds of ammonia crystals, Jupiter has numerous cloud layers, including ammonium hydrosulfide clouds, water crystal clouds and liquid water clouds. The bulk of Jupiter comprises liquid molecular and metallic hydrogen. The planet may have a small solid core occupying as much as 15 percent of its radius.

Saturn

• Saturn is the second largest planet in the solar system. It is roughly 9.4 times the diameter of Earth, and 95 times as massive. Saturn's composition is almost identical to that of Jupiter. Like Jupiter, the motions of its liquid molecular and metallic hydrogen layers produce a very strong magnetosphere. Winds in the upper atmosphere reach speeds of 1,600 feet per second, compared with 360 feet per second on Earth. These winds, combined with the heat rising from its interior, produce the yellow and gold bands that are visible in Saturn's atmosphere. Saturn may have a core with 10 to 20 times the mass of Earth.

Uranus

• The Voyager 2 space mission confirmed the belief, based on the planet's low overall density, that Uranus consists primarily of hydrogen and helium. The outer layer of its atmosphere contains methane gas. As light reflects off the cloud tops below this layer, the methane absorbs red light, giving Uranus its blue-green appearance. Uranus has a diameter four times that of Earth, and is almost 15 times as massive. The planet's liquid core of water, methane and ammonia probably accounts for more than 80 percent of this mass. Unlike Jupiter and Saturn, Uranus does not appear to have any internal source of heat; as a result, it's much colder than these planets. This lack of heat limits the planet's surface activity.

Neptune

• Nearly a sister-planet of Uranus, Neptune is four times the size of Earth, and roughly 17 times as massive. Like Uranus, it has an outer layer of methane gas. However, its blue color is much more vivid, apparently due to an unknown chemical component. Neptune's atmosphere reaches deep into the planet, eventually merging into water. The planet may have an Earth-sized solid core. Its surface winds are three times as strong as Jupiter's, and nine times as strong as Earth's.