K2-21 is 273 light-years from the Sun. The NASA Exoplanet Archive lists 2 planets around this M0.0 star; the first was found in 2015 by transit (K2).
Fly there in 3DK2-21 b goes round its star every 9.33 days, 9 times as often as Mercury goes round the Sun.
| Spectral type | M0.0 |
| Surface temperature | 4,222 K |
| Mass | 0.676023 solar masses |
| Radius | 0.646783 solar radii |
| Luminosity | 0.1035 times the Sun |
| Apparent magnitude | 12.851 |
| Age | about 1 billion years |
| Distance from the Sun | 272.8 light-years (83.6 parsecs) |
| Position (J2000) | RA 340.3038°, Dec -14.4893° |
| Constellation | Aquarius |
| Planet | Year | Orbit | Radius | Mass | Found |
|---|---|---|---|---|---|
| K2-21 b | 9.33 days | 0.0760 AU | 1.84 R⊕ | 4.04 M⊕ estimated | Transit, 2015 |
| K2-21 c | 15.5 days | 0.107 AU | 2.49 R⊕ | 6.76 M⊕ estimated | Transit, 2015 |
Values are the NASA Exoplanet Archive’s composite parameters. A radius marked estimated comes from a mass–radius relation; a mass marked minimum is M sin i. Planet sizes and colours in the 3D view are renderings: none of these worlds has been photographed as more than a point of light.
For a star of 4,222 K, 0.10 times as bright as the Sun, the habitable zone, where starlight could keep water liquid on a rocky surface, runs from about 0.33 to 0.62 AU. None of its known planets orbits inside it. The zone says how much starlight arrives, not whether a planet has water or air. The edges follow Kopparapu et al. (2014), as the 3D view draws them.
The light you see left 273 years ago, around 1750.