K2-222 b
K2-222 b is a super-Earth orbiting the G0 star K2-222 in the constellation Pisces. It lies about 331 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-222 b?
K2-222 b has a radius of 2.28 times that of Earth. Its mass is 7.5 times that of Earth, giving it a density of 3.72 g/cm³ — between that of rocky and gaseous planets.
Is K2-222 b in the Habitable Zone?
K2-222 b orbits inside the inner edge of the habitable zone of K2-222. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-222: 0.860–2.018 AU (conservative: 1.089–1.913 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-222 b
The equilibrium temperature of K2-222 b is about 803 K (530 °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 K2-222 b — one full orbit around K2-222 — lasts 15.4 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.119 AU — closer to its star than Mercury is to the Sun. Its orbit is nearly circular (eccentricity 0.021).
How Was K2-222 b Discovered?
K2-222 b 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 K2-222 b?
K2-222 b is 330.5 light-years (101.3 parsecs) from Earth. Light arriving here tonight left the planet around the year 1696. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 5,816,800 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. K2-222 b scores 0.25, ranking #3,072 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-222
K2-222
- Spectral type
- G0
- Surface temperature
- 5,942 K (Sun: 5,772 K)
- Mass
- 0.94 M☉
- Radius
- 1.07 R☉
- Luminosity
- 1.3400 L☉
- Age
- 7.1 billion years (Sun: 4.6)
Planetary System
K2-222 b is the only planet known to orbit K2-222 so far.
K2-222 b — Complete Data
| Radius | 2.275 Earth radii (0.203 Jupiter radii) |
|---|---|
| Mass | 7.50 Earth masses (0.024 Jupiter masses) |
| Density | 3.72 g/cm³ (Earth: 5.51) |
| Orbital period | 15.39 days |
| Orbital distance | 0.119 AU |
| Eccentricity | 0.021 |
| Equilibrium temperature | 803 K (530 °C) |
| Earth Similarity Index | 0.25 |
| Distance from Earth | 330.5 light-years (101.3 parsecs) |
| Constellation | Pisces |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2026-04-16. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-222 b
Is K2-222 b habitable?
No — K2-222 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-222 b?
K2-222 b is about 331 light-years from Earth in the constellation Pisces. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 5,816,800 years to get there.
How big is K2-222 b compared to Earth?
K2-222 b has 2.28 times the radius of Earth and about 7.5 times its mass.
How long is a year on K2-222 b?
One orbit around K2-222 takes 15.4 Earth days — short enough that 24 of its years would fit into one Earth year.
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