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The smallest known extrasolar planet that is likely a "gas planet" is Kepler-138d, which has the same mass as Earth but is 60% larger and therefore has a density that indicates a thick gas envelope. [16] A low-mass gas planet can still have a radius resembling that of a gas giant if it has the right temperature. [17]
For the very hottest gas giants, with temperatures above 1400 K (2100 °F, 1100 °C) or cooler planets with lower gravity than Jupiter, the silicate and iron cloud decks are predicted to lie high up in the atmosphere. The predicted Bond albedo of a class V planet around a Sun-like star is 0.55, due to reflection by the cloud decks.
A giant planet, sometimes referred to as a jovian planet (Jove being another name for the Roman god Jupiter), is a diverse type of planet much larger than Earth. Giant planets are usually primarily composed of low- boiling point materials ( volatiles ), rather than rock or other solid matter, but massive solid planets can also exist.
[14] [15] The largest planetesimals can grow much faster via pebble accretion, [10] but if the formation or delivery of pebbles is rapid numerous Earth-mass planets form instead of a few giant planet cores. [16] As the largest objects approach Earth-mass the radius from which pebbles are accreted is limited by the Hill radius. [3]
PSO J318.5−22 is an extrasolar object of planetary mass that does not orbit a parent star, it is an analog to directly imaged young gas giants. [6] There is no consensus yet among astronomers whether the object should be referred to as a sub-brown dwarf , [ 7 ] [ 8 ] as a rogue planet [ 9 ] [ 10 ] or as a young brown dwarf .
“The planet is basically super fluffy” because it's made mostly of light gases rather than solids, lead author Khalid Barkaoui of Massachusetts Institute of Technology said in a statement
Astronomers say they have uncovered an unusual planet that’s about 50% bigger than Jupiter and somehow still the second lightest planet ever found. Unusual giant planet as fluffy as cotton candy ...
For the giant planets, the "radius" is defined as the distance from the center at which the atmosphere reaches 1 bar of atmospheric pressure. [ 11 ] Because Sedna and 2002 MS 4 have no known moons, directly determining their mass is impossible without sending a probe (estimated to be from 1.7x10 21 to 6.1×10 21 kg for Sedna [ 12 ] ).