K2-331 c
K2-331 c is a mini-Neptune orbiting K2-331 in the constellation Cancer. It lies about 690 light-years from Earth and was discovered in 2021 using the transit method.
How Big Is K2-331 c?
K2-331 c has a radius of 2.72 times that of Earth.
Is K2-331 c in the Habitable Zone?
The position of K2-331 c relative to the habitable zone of K2-331 cannot be precisely determined from the available orbital data.
Habitable zone of K2-331: 0.845–1.980 AU (conservative: 1.070–1.877 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Temperature on K2-331 c
The equilibrium temperature of K2-331 c is about 673 K (400 °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.
Orbit and Year Length
A year on K2-331 c — one full orbit around K2-331 — lasts 23.0 Earth days, shorter than Mercury's 88-day year.
How Was K2-331 c Discovered?
K2-331 c was discovered in 2021 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 K2-331 c?
K2-331 c is 689.6 light-years (211.4 parsecs) from Earth. Light arriving here tonight left the planet around the year 1337. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 12,136,960 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. K2-331 c scores 0.25, ranking #3,101 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-331
K2-331
- Surface temperature
- 5,994 K (Sun: 5,772 K)
- Mass
- 1.10 M☉
- Radius
- 1.06 R☉
The K2-331 Planetary System
K2-331 c is one of 2 known planets in the K2-331 system. Its siblings:
- K2-331 b (Super Earth)
K2-331 c — Complete Data
| Radius | 2.720 Earth radii (0.243 Jupiter radii) |
|---|---|
| Orbital period | 23.00 days |
| Equilibrium temperature | 673 K (400 °C) |
| Earth Similarity Index | 0.25 |
| Distance from Earth | 689.6 light-years (211.4 parsecs) |
| Constellation | Cancer |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2021 |
Data: NASA Exoplanet Archive, last updated 2021-08-23. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-331 c
Is K2-331 c habitable?
K2-331 c is not known to orbit within the habitable zone of K2-331, and as a mini-Neptune it is an unlikely candidate for life as we know it.
How far away is K2-331 c?
K2-331 c is about 690 light-years from Earth in the constellation Cancer. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 12,136,960 years to get there.
How big is K2-331 c compared to Earth?
K2-331 c has 2.72 times the radius of Earth.
How long is a year on K2-331 c?
One orbit around K2-331 takes 23.0 Earth days — short enough that 16 of its years would fit into one Earth year.
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