K2-38 c
K2-38 c is a super-Earth orbiting the G2 V star K2-38 in the constellation Scorpius. It lies about 629 light-years from Earth and was discovered in 2016 using the transit method.
How Big Is K2-38 c?
K2-38 c has a radius of 2.29 times that of Earth. Its mass is 8.3 times that of Earth, giving it a density of 3.80 g/cm³ — between that of rocky and gaseous planets.
Is K2-38 c in the Habitable Zone?
K2-38 c orbits inside the inner edge of the habitable zone of K2-38. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-38: 0.786–1.853 AU (conservative: 0.995–1.757 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-38 c
The equilibrium temperature of K2-38 c is about 916 K (643 °C) — hot enough to melt many metals. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 117 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-38 c — one full orbit around K2-38 — lasts 10.6 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.095 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.16).
How Was K2-38 c Discovered?
K2-38 c was discovered in 2016 using the transit method, with observations from K2.
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is K2-38 c?
K2-38 c is 628.5 light-years (192.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 1398. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 11,061,600 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. K2-38 c scores 0.24, ranking #3,276 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-38
K2-38
- Spectral type
- G2 V
- Surface temperature
- 5,731 K (Sun: 5,772 K)
- Mass
- 1.03 M☉
- Radius
- 1.06 R☉
- Luminosity
- 1.0900 L☉
- Age
- 6.7 billion years (Sun: 4.6)
The K2-38 Planetary System
K2-38 c is one of 2 known planets in the K2-38 system. Its siblings:
- K2-38 b (Super Earth)
K2-38 c — Complete Data
| Radius | 2.290 Earth radii (0.204 Jupiter radii) |
|---|---|
| Mass | 8.30 Earth masses (0.026 Jupiter masses) |
| Density | 3.80 g/cm³ (Earth: 5.51) |
| Orbital period | 10.56 days |
| Orbital distance | 0.095 AU |
| Eccentricity | 0.161 |
| Equilibrium temperature | 916 K (643 °C) |
| Stellar irradiation | 117.00× Earth |
| Earth Similarity Index | 0.24 |
| Distance from Earth | 628.5 light-years (192.7 parsecs) |
| Constellation | Scorpius |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2016 |
Data: NASA Exoplanet Archive, last updated 2023-01-18. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-38 c
Is K2-38 c habitable?
No — K2-38 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-38 c?
K2-38 c is about 629 light-years from Earth in the constellation Scorpius. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 11,061,600 years to get there.
How big is K2-38 c compared to Earth?
K2-38 c has 2.29 times the radius of Earth and about 8.3 times its mass.
How long is a year on K2-38 c?
One orbit around K2-38 takes 10.6 Earth days — short enough that 35 of its years would fit into one Earth year.
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