HAT-P-21 is 904 light-years from the Sun. The NASA Exoplanet Archive lists 1 planet around this G3 star; the first was found in 2010 by transit (HATNet).
Fly there in 3DHAT-P-21 b goes round its star every 4.12 days, 21 times as often as Mercury goes round the Sun.
| Spectral type | G3 |
| Surface temperature | 5,588 K |
| Mass | 1.24 solar masses |
| Radius | 1.21 solar radii |
| Luminosity | 1.52 times the Sun |
| Apparent magnitude | 11.459 |
| Age | about 10.2 billion years |
| Distance from the Sun | 904.4 light-years (277.3 parsecs) |
| Position (J2000) | RA 171.2749°, Dec 41.0280° |
| Constellation | Ursa Major |
| Planet | Year | Orbit | Radius | Mass | Found |
|---|---|---|---|---|---|
| HAT-P-21 b | 4.12 days | 0.0504 AU | 12.442 R⊕ | 1547.8 M⊕ | Transit, 2010 |
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.