| Discovery | |
|---|---|
| Discovery date | 2016 |
| Orbital characteristics | |
| Eccentricity | <0.05 |
| 17.7 days | |
| Physical characteristics | |
| 2.2R🜨 | |
| Mass | 5.47M🜨 |
Meandensity | 2.83 g/cm3 |
| Temperature | 266 K |
K2-332 b (alsoEPIC 211579112.01)[1][2] is apotentially habitableSuper-Earth orMini-Neptune exoplanet with a radius of 2.2 earths. It is in theempirical habitable zone, receiving 1.17 times the light that Earth gets from the sun. Its star,K2-332, is typeM4V, with a temperature of ~3300 K.[3] It wasdetected using the transit method in 2016 and is 402light-years away.[4]
The planet is confirmed to exist and was discovered by the K2 "Second Light" mission in 2016. It was originally referred to by its EPIC designation. The average transit time is 2 hours and 2 minutes and the average depth is 0.6508%.[1][2][4][5] The object's star is within the2MASS catalog.[5]
The planet has an estimated mass of 5.47 earths, and at a radius of more than twice that of the Earth, the density corresponds to that of awatery orgaseous Mini-Neptune rather than a rocky Super-Earth. It has anequilibrium temperature of 266 K (−7 °C; 19 °F), somewhat higher than Earth's.[3][5]
The planet orbits within the inner part of the habitable zone, about 1/3 of the way between therunaway G limit for Super-Earths and the absolute inner edge. Its orbital period is 17.7 days, but the planet has an unknownsemi-major axis. Its star is a dim red dwarf with about 20% the mass and size of the sun. In its habitable-zone orbit, the planet receives 1.17 times theinsolation Earth gets from the sun.[1][2][3][4][5]
The planet is large (over 2 Earth-radii) and has a low density consistent with that of a watery orNeptune-like planet and not a silicate planet or a partiallymetallic planet like Earth. This compromises its habitability, for a solid surface is required for life to develop spontaneously on a planet.[3][4][5]
However, 2021 studies show that sub-Neptunes have an abundance ofwater and life-friendly molecules (nitrogen,oxygen,CO2, etc.) in their atmospheres, and the area with habitable temperatures and pressures is fairly stable. As a result, K2-332 b could be a habitable planet despite its extremely low density. If the system has a leftoverdust disk orasteroid/comet belt,panspermia ofmicrobial life from a terrestrial planet orearthlike moon could occur, and the organisms would have enough time toreproduce before dying due to the harsh conditions.[6] 2019 studies of theTOI-270 system support the notion that Mini-Neptunes have life-friendly atmospheres rich inorganic matter.[7]
The planet is very close to its star with a low eccentricity, so it is likely to betidally locked, with one side always facing the star. In this case, the dayside would be extremely hot, while the nightside would be cold enough to freeze an atmosphere on a terrestrial planet, where the terminator line and adjacenttwilight region would be the only habitable parts of the planet. This occurs in 4.5Gyrs in planets orbiting stars M1 and later, and in 1 Gyr in planets around stars M7 and later.[8] However, oceanic currents and wind can distribute heat evenly around a planet (any planet, not just an Earth-size one), warming the nightside past the freezing point of the atmosphere and cooling the dayside to below 100 °C. The area in the life-friendly pressure tier of the atmosphere that would also have habitable temperatures would then extend to 55° in both hemispheres on the dayside and around the nightside near the equator, with a maximum temperature of ~42 °F (6 °C). For higher levels of carbon dioxide, this area could even extend around the entire planet (minus thenadir and highpolar regions).[9]
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