K2-229b
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 Artist impression of K2-229b | |
| Discovery | |
|---|---|
| Discovery site | Kepler Space Observatory |
| Discovery date | 2018 |
| Transit | |
| Orbital characteristics | |
| 0.012888 (± 0.000130)[1] AU | |
| Eccentricity | 0[1] |
| 0.584249 (± 0.000014)[1] d 14.02 h | |
| Inclination | 83.9 (± 2.8)[1] |
| Star | K2-229 |
| Physical characteristics | |
| 1.164±0.066[1] R🜨 | |
| Mass | 2.59±0.43[1] M🜨 |
Mean density | 8.9±2.1 g cm−3 |
| 1.91 +0.59 −0.48 g | |
| Temperature | 1,960 K (1,690 °C; 3,070 °F) (equilibrium)[1] 2,332 K (2,059 °C; 3,738 °F) (day side)[2] |
K2-229b (previously designated EPIC 228801451.01) is an extremely hot, solid, iron-rich exoplanet in a close orbit around the active K-dwarf K2-229 in the constellation Virgo, 335 light years away from Earth.[3]
Mass, radius, and temperature
K2-229b is a relatively Earth-sized planet, first identified using the transit method, where a planet passes in front of its host star and blocks a tiny fraction of its light. When the planet was first discovered, only its radius was known. It was determined to be 1.165 R🜨, or about 16.5% larger than Earth.[1] A planet of this size is most likely rocky with a solid surface, like Earth itself. However, radial velocity measurements using the HARPS spectrograph revealed that K2-229b was far denser and more massive than initially expected. The planet has a mass of 2.59 M🜨 and an extremely high density of about 8.9 g/cm3,[1] giving it about 91% more surface gravity than Earth. The unusually high mass and density of K2-229b indicates a Mercury-like composition dominated by an iron core taking up about 70% of the planet's mass.[4]
Due to its extremely tight orbit, K2-229b is one of the hottest planets yet found. It has an equilibrium temperature of 1,960 K (1,690 °C; 3,070 °F),[1] hot enough to melt iron. The day side has an even higher temperature in excess of 2,330 K (2,060 °C; 3,730 °F).[4]
Orbit and rotation
K2-229b has one of the shortest orbital periods known, with one full orbit taking just 0.584 days (14 hours) to complete. The planet orbits its host star at a distance of 0.012888 AU, nearly 100 times closer in than Earth.[1] For comparison, our Solar System's innermost planet, Mercury, takes 88 days to orbit at 0.39 AU. K2-229b has an orbital eccentricity of 0 and is most likely tidally locked with its host star.
Host star
K2-229b orbits the orange dwarf star K2-229, which is about 79% the radius and 84% the mass of the Sun, with a temperature of 5185 K and an age of about 5.4 billion years.[1] For comparison, the Sun has a temperature of 5778 K and is 4.5 billion years old. K2-229 has a visual magnitude of 10.985, too faint to be seen without a telescope. It is noted for being extremely active.[4]
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