K2-239 c
K2-239 c is a terrestrial planet orbiting the M3.0 V star K2-239 in the constellation Sextans. It lies about 101 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-239 c?
K2-239 c has a radius of 1.00 times that of Earth.
Is K2-239 c in the Habitable Zone?
K2-239 c orbits inside the inner edge of the habitable zone of K2-239. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-239: 0.104–0.270 AU (conservative: 0.131–0.256 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-239 c
The equilibrium temperature of K2-239 c is about 427 K (154 °C) — hotter than anywhere on Earth. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C.
Orbit and Year Length
A year on K2-239 c — one full orbit around K2-239 — lasts 7.78 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.058 AU — closer to its star than Mercury is to the Sun.
How Was K2-239 c Discovered?
K2-239 c was discovered in 2018 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 K2-239 c?
K2-239 c is 101.4 light-years (31.1 parsecs) from Earth. Light arriving here tonight left the planet around the year 1925. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,784,640 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. K2-239 c scores 0.54, ranking #211 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-239
K2-239
- Spectral type
- M3.0 V
- Surface temperature
- 3,420 K (Sun: 5,772 K)
- Mass
- 0.40 M☉
- Radius
- 0.36 R☉
- Luminosity
- 0.0160 L☉
The K2-239 Planetary System
K2-239 c is one of 3 known planets in the K2-239 system. Its siblings:
K2-239 c — Complete Data
| Radius | 1.000 Earth radii (0.089 Jupiter radii) |
|---|---|
| Orbital period | 7.78 days |
| Orbital distance | 0.058 AU |
| Equilibrium temperature | 427 K (154 °C) |
| Earth Similarity Index | 0.54 |
| Distance from Earth | 101.4 light-years (31.1 parsecs) |
| Constellation | Sextans |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2018-06-26. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-239 c
Is K2-239 c habitable?
No — K2-239 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-239 c?
K2-239 c is about 101 light-years from Earth in the constellation Sextans. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,784,640 years to get there.
How big is K2-239 c compared to Earth?
K2-239 c has 1.00 times the radius of Earth.
How long is a year on K2-239 c?
One orbit around K2-239 takes 7.8 Earth days — short enough that 47 of its years would fit into one Earth year.
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