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K2-21, also known as EPIC 206011691, is a red dwarf star located 273 light-years (84 parsecs) away in the constellation Aquarius. It hosts two known exoplanets, discovered in 2015 by the transit method as part of Kepler's K2 mission.[3] Both planets have significantly lower densities than Earth, indicating that they are not rocky planets and are better described as mini-Neptunes. The inner planet, K2-21b, is less dense than the outer planet, K2-21c.[5]

The K2-21 planetary system[5]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
Eccentricity Inclination Radius
b 1.59+0.52
−0.44
 M🜨
0.0731+0.0057
−0.0067
[3]
9.3238+0.0002
−0.0001
88.54+0.49
−0.59
°
1.93±0.07 R🜨
c 3.88+1.22
−1.07
 M🜨
0.1026+0.0079
−0.0094
[3]
15.5017±0.0002 89.02+0.33
−0.41
°
2.25±0.05 R🜨

References


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