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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]
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
- ^ "Finding the constellation which contains given sky coordinates". djm.cc. 2 August 2008.
- ^ a b c d e f Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b c d e f g h Petigura, Erik A.; et al. (2015). "Two Transiting Earth-Size Planets Near Resonance Orbiting a Nearby Cool Star". The Astrophysical Journal. 811 (2) 102. arXiv:1507.08256. Bibcode:2015ApJ...811..102P. doi:10.1088/0004-637X/811/2/102.
- ^ a b c d "K2-21". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 24 May 2023.
- ^ a b El Moutamid, Maryame; et al. (April 2023). "Mass derivation of planets K2-21b and K2-21c from transit timing variations". Monthly Notices of the Royal Astronomical Society. 520 (3): 4226–4234. arXiv:2305.11359. Bibcode:2023MNRAS.520.4226E. doi:10.1093/mnras/stad238.
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