Neptunian exoplanets are similar in size to the

ice giant An ice giant is a giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two ice giants in the Solar System: Uranus and Neptune. In astrophysics and planetary science ...

Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...

and

Uranus Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured ice giant. Most of the planet is made of water, ammonia, and methane in a Supercritical fluid, supercritical phase of matter, which astronomy calls "ice" or Volatile ( ...

in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

. Neptunian exoplanets may have a mixture of interiors though all would be rocky with heavier metals at their cores. Neptunian planets typically have

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

- and

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

-dominated atmospheres. There are several recognized subtypes of Neptunian exoplanets: *

Hot Neptune A hot Neptune is a type of giant planet with a mass similar to that of Neptune or Uranus orbiting close to its star, normally within less than 1 AU. The first hot Neptune to be discovered with certainty was Gliese 436 b (Awohali) in 2007, an ex ...

– orbiting close to its star * Helium planet – a hypothetical type that can form from hot Neptune via hydrogen

evaporation Evaporation is a type of vaporization that occurs on the Interface (chemistry), surface of a liquid as it changes into the gas phase. A high concentration of the evaporating substance in the surrounding gas significantly slows down evapora ...

, leaving a helium-dominated atmosphere *

Mini-Neptune A Mini-Neptune (sometimes known as a gas dwarf or transitional planet) is a planet less massive than Neptune but resembling Neptune in that it has a thick hydrogen-helium atmosphere, probably with deep layers of ice, rock or liquid oceans (made o ...

– considerably smaller than Neptune but still having a thick hydrogen-helium envelope, relatively common *

Super-puff A super-puff is a type of exoplanet with a mass only a few times larger than Earth's but with a radius larger than that of Neptune, giving it a very low mean density.

– inflated planets with unusually low mean

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

Hycean planet A hycean planet ( ) is a Hypothetical astronomical object, hypothetical type of planet with liquid water oceans underneath a hydrogen-rich atmosphere. Definition The term ''hycean'' is a Blend word, portmanteau of ''hydrogen'' and ''ocean'' ...

– a hypothetical transitional type to

ocean planet An ocean world, ocean planet or water world is a type of planet or natural satellite that contains a substantial amount of water in the form of oceans, as part of its hydrosphere, either beneath the planetary surface, surface, as subsurface ...

s with a thin, hydrogen-helium-dominated atmosphere overlaying a liquid water ocean

List of Neptunian exoplanets

HAT

HAT-P-26 HAT-P-26 is a K-type main-sequence star located about away in the constellation of Virgo. A survey in 2015 did not find any stellar companions in orbit around it, although a red dwarf companion with a temperature is suspected on wide orb ...

b *

HAT-P-11b HAT-P-11b (or Kepler-3b) is an extrasolar planet orbiting the star HAT-P-11. It was discovered by the HATNet Project team in 2009 using the transit method, and submitted for publication on 2 January 2009. This planet is located approximatel ...

GJ

* GJ 436b

TOI

* TOI-1231 b

OGLE

* OGLE-2005-BLG-390L b

References

Neptunian Neptune has appeared in fiction since shortly after its 1846 discovery, albeit infrequently. It initially made appearances indirectly—e.g. through its inhabitants—rather than as a setting. The earliest stories set on Neptune itself portrayed ...

Types of planet {{Exoplanet-stub