K2-72
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h 18m 29.27s[1] |
| Declination | −09° 36′ 44.6″[1] |
| Characteristics | |
| Spectral type | M?V |
| Astrometry | |
| Distance | 227.7[1] ly (69.8[1] pc) |
| Details | |
| Mass | 0.217 ± 0.081[1] M☉ |
| Radius | 0.232 ± 0.56[1] R☉ |
| Surface gravity (log g) | 5.048±0.075[1] cgs |
| Temperature | 3497 ± 150[1] K |
| Other designations | |
EPIC 206209135, 2MASS J22182923-0936444 | |
K2-72 is a cool red dwarf star located about 227 light-years (70 pc) away from the Earth in the constellation of Aquarius. It is known to host four planets, all smaller than Earth, with two of them residing within the habitable zone.
Nomenclature and history
K2-72 also has the 2MASS catalogue number J22182923-0936444.
The star's planetary companions were discovered by NASA's Kepler Mission, a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits move in front of their stars from the perspective of Earth. The name K2-72 derives directly from the fact that the star is the catalogued 72nd star discovered by the K2 mission to have confirmed planets.
The designation b, c, d, and e derives from the order of discovery. The designation of b is given to the first planet orbiting a given star, and e to the last.[2] In the case of K2-72, there were four planets, so only letters b to e are used.
Stellar characteristics
K2-72 is a M-type star that is approximately 21% the mass of and 23% the radius of the Sun. It has a surface temperature of 3497 K and its age is unknown. In comparison, the Sun is about 4.6 billion years old[3] and has a surface temperature of 5778 K.[4]
The star's apparent magnitude, or how bright it appears from Earth's perspective, is unknown.
Planetary system
The star is known to host four planets, with two orbiting in the habitable zone. All are smaller than Earth by some magnitude.
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | — | 0.037 | 5.5774 | — | — | 0.75±0.20 R⊕ |
| d | — | 0.046 | 7.76 | — | — | 0.76±0.20 R⊕ |
| c | — | 0.0722 | 15.1871 | — | — | 0.86±0.22 R⊕ |
| e | — | 0.098 | 24.1669 | — | — | 0.82±0.22 R⊕ |
References
- 1 2 3 4 5 6 7 8 9 "NASA Exoplanet Archive". NASA Exoplanet Science Institute. 18 July 2016. Retrieved 2016-07-18.
- ↑ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707
[astro-ph.SR]. - ↑ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
- ↑ Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.