K2-21
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. 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.
| 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 |
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 |
15.5017±0.0002 | — | 89.02+0.33 −0.41° |
2.25±0.05 R🜨 |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h 41m 12.88625s |
| Declination | −14° 29′ 20.3492″ |
| Apparent magnitude (V) | 12.85 |
| Characteristics | |
| Evolutionary stage | Main sequence |
| Spectral type | M0.0±0.5V |
| Apparent magnitude (B) | 14.14±0.06 |
| Apparent magnitude (V) | 12.85±0.02 |
| Apparent magnitude (G) | 12.268±0.003 |
| Apparent magnitude (J) | 10.251±0.021 |
| Apparent magnitude (H) | 9.633±0.022 |
| Apparent magnitude (K) | 9.417±0.020 |
| Astrometry | |
| Radial velocity (Rv) | 3.54±0.82 km/s |
| Proper motion (μ) | RA: 20.672 mas/yr Dec.: -78.914 mas/yr |
| Parallax (π) | 11.9662 ± 0.0150 mas |
| Distance | 272.6 ± 0.3 ly (83.6 ± 0.1 pc) |
| Details | |
| Mass | 0.64±0.11 M☉ |
| Radius | 0.60±0.10 R☉ |
| Luminosity (bolometric) | 0.086±0.064 L☉ |
| Temperature | 4043±375 K |
| Metallicity [Fe/H] | −0.11±0.13 dex |
| Age | >1 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
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