K2-233 b
K2-233 b is a super-Earth orbiting the K3 star K2-233 in the constellation Libra. It lies about 220 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-233 b?
K2-233 b has a radius of 1.32 times that of Earth. Its mass is 2.4 times that of Earth, giving it a density of 5.70 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is K2-233 b in the Habitable Zone?
K2-233 b orbits inside the inner edge of the habitable zone of K2-233. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-233: 0.387–0.943 AU (conservative: 0.490–0.894 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-233 b
The equilibrium temperature of K2-233 b is about 1,127 K (854 °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 269 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-233 b — one full orbit around K2-233 — lasts 2.47 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.033 AU — closer to its star than Mercury is to the Sun.
How Was K2-233 b Discovered?
K2-233 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 K2-233 b?
K2-233 b is 220.2 light-years (67.5 parsecs) from Earth. Light arriving here tonight left the planet around the year 1806. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,875,520 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. K2-233 b scores 0.29, ranking #1,825 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-233
K2-233
- Spectral type
- K3
- Surface temperature
- 4,796 K (Sun: 5,772 K)
- Mass
- 0.79 M☉
- Radius
- 0.71 R☉
- Age
- 0.4 billion years (Sun: 4.6)
The K2-233 Planetary System
K2-233 b is one of 3 known planets in the K2-233 system. Its siblings:
K2-233 b — Complete Data
| Radius | 1.315 Earth radii (0.117 Jupiter radii) |
|---|---|
| Mass | 2.40 Earth masses (0.008 Jupiter masses) |
| Density | 5.70 g/cm³ (Earth: 5.51) |
| Orbital period | 2.47 days |
| Orbital distance | 0.033 AU |
| Equilibrium temperature | 1,127 K (854 °C) |
| Stellar irradiation | 269.00× Earth |
| Earth Similarity Index | 0.29 |
| Distance from Earth | 220.2 light-years (67.5 parsecs) |
| Constellation | Libra |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2025-08-28. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-233 b
Is K2-233 b habitable?
No — K2-233 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-233 b?
K2-233 b is about 220 light-years from Earth in the constellation Libra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,875,520 years to get there.
How big is K2-233 b compared to Earth?
K2-233 b has 1.32 times the radius of Earth and about 2.4 times its mass.
How long is a year on K2-233 b?
One orbit around K2-233 takes 2.5 Earth days — short enough that 148 of its years would fit into one Earth year.
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