K2-12 b
K2-12 b is a mini-Neptune orbiting K2-12 in the constellation Leo. It lies about 1,065 light-years from Earth and was discovered in 2015 using the transit method.
How Big Is K2-12 b?
K2-12 b has a radius of 2.44 times that of Earth. Its mass is 5.2 times that of Earth, giving it a density of 1.60 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is K2-12 b in the Habitable Zone?
K2-12 b orbits inside the inner edge of the habitable zone of K2-12. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-12: 0.813–1.921 AU (conservative: 1.030–1.821 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 K2-12 b
The equilibrium temperature of K2-12 b is about 1,026 K (753 °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 185 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-12 b — one full orbit around K2-12 — lasts 8.28 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.079 AU — closer to its star than Mercury is to the Sun. Its orbit is highly elliptical (eccentricity 0.50), swinging dramatically closer to and farther from its star.
How Was K2-12 b Discovered?
K2-12 b was discovered in 2015 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 K2-12 b?
K2-12 b is 1,064.5 light-years (326.4 parsecs) from Earth. Light arriving here tonight left the planet about 1,065 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 18,735,200 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. K2-12 b scores 0.24, ranking #3,328 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-12
K2-12
- Surface temperature
- 5,672 K (Sun: 5,772 K)
- Mass
- 0.97 M☉
- Radius
- 1.12 R☉
- Age
- 8.9 billion years (Sun: 4.6)
Planetary System
K2-12 b is the only planet known to orbit K2-12 so far.
K2-12 b — Complete Data
| Radius | 2.440 Earth radii (0.218 Jupiter radii) |
|---|---|
| Mass | 5.20 Earth masses (0.016 Jupiter masses) |
| Density | 1.60 g/cm³ (Earth: 5.51) |
| Orbital period | 8.28 days |
| Orbital distance | 0.079 AU |
| Eccentricity | 0.500 |
| Equilibrium temperature | 1,026 K (753 °C) |
| Stellar irradiation | 185.00× Earth |
| Earth Similarity Index | 0.24 |
| Distance from Earth | 1,064.5 light-years (326.4 parsecs) |
| Constellation | Leo |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2015 |
Data: NASA Exoplanet Archive, last updated 2023-04-17. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-12 b
Is K2-12 b habitable?
No — K2-12 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-12 b?
K2-12 b is about 1,065 light-years from Earth in the constellation Leo. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 18,735,200 years to get there.
How big is K2-12 b compared to Earth?
K2-12 b has 2.44 times the radius of Earth and about 5.2 times its mass.
How long is a year on K2-12 b?
One orbit around K2-12 takes 8.3 Earth days — short enough that 44 of its years would fit into one Earth year.
Explore K2-12 b in the app
Browse, filter and compare 6,000+ exoplanets on iPhone, iPad and Apple Watch — with habitable-zone views, widgets and offline data.
