K2-38b
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 but about 12 times more massive, indicating a composition rich in iron and an extremely high surface gravity. The planet is within K2 Campaign 2, in the constellation Scorpius.
Discovery[1] | |
---|---|
Discovery site | Kepler Space Observatory |
Discovery date | 2016 |
Transit | |
Orbital characteristics | |
0.0506 (± 0.0008)[2] AU | |
Eccentricity | null[2] |
4.01593 (± 0.0005)[2] d | |
Inclination | 87.28 +1.88 −3.08[2] |
Star | K2-38 |
Physical characteristics | |
Mean radius | 1.55 (± 0.16)[2] R⊕ |
Mass | 12.0 (± 2.9)[2] M⊕ |
Mean density | 17.5+8.5 −6.2 g cm−3 |
4.99+2.72 −1.88 g | |
Temperature | 1,184 K (911 °C; 1,672 °F)[1] |
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⊕,[2] 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 made almost entirely of iron,[1] with a mass of about 12.0 M⊕ and a density of about 17.5 g/cm3.[2] This makes it one of the densest exoplanets ever discovered. The planet has a surface gravity around 5 times that of Earth, about twice that of the planet Jupiter. K2-38b is also very hot, with an equilibrium temperature of 1,184 K (911 °C; 1,672 °F), hot enough to melt some types of metals.[1]
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 0.0506 AU. For comparison, Mercury orbits every 88 days at 0.38 AU from the Sun. The eccentricity of K2-38's orbit is unknown.[2]
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.[2]
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.[1]
See also
- Mega-Earth
- K2-3d, another iron-rich planet found by the K2 mission
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.
- "K2-38 b CONFIRMED PLANET OVERVIEW PAGE". NASA Exoplanet Archive. Retrieved 2018-01-20.