| Discovery | |
|---|---|
| Discovery site | Kepler Space Observatory |
| Discovery date | 2016 |
| Detection method | Transit |
| Orbital characteristics | |
| Semi-major axis | 0.04994 −0.00049 AU |
| Eccentricity | 0.197 −0.060 |
| Orbital period (sidereal) | 4.01593 (± 0.0005) d |
| Inclination | 88.36 −0.15 |
| Star | K2-38 |
| Physical characteristics | |
| Mean radius | 1.54±0.14 R🜨 |
| Mass | 7.3 −1.0 ME |
| Mean density | 11.0 −3.7 g cm |
| Surface gravity | 3.08 −0.74 g |
| Temperature | 1,266 K (993 °C; 1,819 °F) |
K2-38b, also designated EPIC 204221263 b, is a massive rocky exoplanet closely orbiting a Sun-like star and is one of the densest planets ever found. Discovered in 2016 by Crossfield et al. and later characterized by Sinukoff et al., K2-38b is a rocky super-Earth about 55% larger than Earth (nearly 20,000 km wide) but about 12 times more massive (around 7.2*10^25 kg, a bit less than Uranus) indicating a composition rich in iron and an extremely high surface gravity. The planet is within K2 Campaign 2, in the constellation Scorpius.
Characteristics
Mass, radius, and temperature
K2-38b is a massive rocky exoplanet significantly larger and more massive than Earth. It has a radius of 1.55 R🜨, close to the 1.6 R🜨 limit where planets would begin to accumulate thick hydrogen-helium atmospheres and become something similar to a Mini-Neptune. However, K2-38b is instead a very dense terrestrial planet. Initially it was believed planet is made almost entirely of iron, with a mass of about 12.0 ME and a density of about 17.5 g/cm. This made it one of the densest exoplanets ever discovered. Measurement in 2020 have resulted in lower mass of 7.3
−1.0 ME, and less extreme constraints on composition though.
Orbit
K2-38b has a very tight orbit around its host star. The planet takes just 4 days to complete a single orbit at a distance of about 0.05 AU. For comparison, Mercury orbits every 88 days at 0.38 AU from the Sun. The eccentricity of K2-38's orbit is slightly larger than that of Mars.
Host star
The parent star K2-38 is a G2 main-sequence star, similar to our own Sun. It is 1.10 R☉ and 1.07 M☉, with a temperature of 5757 K and an unknown age. For comparison, the Sun has a temperature of 5778 K and is about 4.5 billion years old.
The visual magnitude of K2-38, or how bright it appears to the human eye, is 11.39. Therefore, it is far too dim to be seen without a telescope.
See also
References
- ^ Sinukoff, Evan; et al. (2016). "Eleven Multiplanet Systems from K2 Campaigns 1 and 2 and the Masses of Two Hot Super-Earths". The Astrophysical Journal. 827 (1). 78. arXiv:1511.09213. Bibcode:2016ApJ...827...78S. doi:10.3847/0004-637X/827/1/78.
- ^ Toledo-Padrón, B.; et al. (2020), "Characterization of the K2-38 planetary system", Astronomy & Astrophysics, 641: A92, arXiv:2007.01081, doi:10.1051/0004-6361/202038187, S2CID 220302044
- ^ "K2-38 b CONFIRMED PLANET OVERVIEW PAGE". NASA Exoplanet Archive. Retrieved 2018-01-20.