National Library of Medicine (opens in new tab). For perspective, methane crystallizes at minus 296 Fahrenheit (minus 183 degrees Celsius), according to the U.S. This is because Uranus and Neptune have more atmospheric water and other ice-forming molecules, such as methane, hydrogen sulfide and phosphene, that crystallize into clouds in the planets' frigid conditions, according to the Planetary Society (opens in new tab).

Jupiter and Saturn are sometimes called the gas giants, whereas the more distant Uranus and Neptune have been nicknamed the ice giants. If you were to order the planets by size from smallest to largest they would be Mercury, Mars, Venus, Earth, Neptune, Uranus, Saturn and Jupiter. They're also mostly made of gases like hydrogen, helium and ammonia rather than of rocky surfaces, although astronomers believe some or all of them may have solid cores. The four large outer worlds - Jupiter, Saturn, Uranus and Neptune - are sometimes called the Jovian or 'Jupiter-like' planets because of their enormous size relative to the terrestrial planets. Pluto also has a rocky, albeit frozen, surface but has never been grouped with the four terrestrials. The inner four planets closest to the sun - Mercury, Venus, Earth and Mars - are often called the ' terrestrial planets' because their surfaces are rocky. Related: 15 stunning places on Earth that look like they're from another planet Types of planets in the solar system The alleged 'Planet Nine,' also called 'Planet X,' is believed to be about 10 times the mass of Earth and 5,000 times the mass of Pluto.

Pluto is truly way out there and on a wildly tilted, elliptical orbit (two of the several reasons it was demoted).Īstronomers, however, are still hunting for another possible planet in our solar system, a true ninth planet, after mathematical evidence of its existence was revealed on Jan. If you insist on including Pluto, it would come after Neptune on the list.

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