K2-203 b
K2-203 b is a super-Earth orbiting K2-203 in the constellation Cetus. It lies about 542 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-203 b?
K2-203 b has a radius of 1.27 times that of Earth.
Is K2-203 b in the Habitable Zone?
K2-203 b orbits inside the inner edge of the habitable zone of K2-203. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-203: 0.454–1.097 AU (conservative: 0.575–1.040 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-203 b
The equilibrium temperature of K2-203 b is about 738 K (465 °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 K2-203 b — one full orbit around K2-203 — lasts 9.70 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.082 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.23).
How Was K2-203 b Discovered?
K2-203 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 K2-203 b?
K2-203 b is 541.9 light-years (166.1 parsecs) from Earth. Light arriving here tonight left the planet around the year 1485. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 9,537,440 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. K2-203 b scores 0.31, ranking #1,116 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-203
K2-203
- Surface temperature
- 5,026 K (Sun: 5,772 K)
- Mass
- 0.79 M☉
- Radius
- 0.77 R☉
- Luminosity
- 0.3370 L☉
- Age
- 6.9 billion years (Sun: 4.6)
Planetary System
K2-203 b is the only planet known to orbit K2-203 so far.
K2-203 b — Complete Data
| Radius | 1.265 Earth radii (0.113 Jupiter radii) |
|---|---|
| Orbital period | 9.70 days |
| Orbital distance | 0.082 AU |
| Eccentricity | 0.230 |
| Equilibrium temperature | 738 K (465 °C) |
| Earth Similarity Index | 0.31 |
| Distance from Earth | 541.9 light-years (166.1 parsecs) |
| Constellation | Cetus |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2024-11-20. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-203 b
Is K2-203 b habitable?
No — K2-203 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-203 b?
K2-203 b is about 542 light-years from Earth in the constellation Cetus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 9,537,440 years to get there.
How big is K2-203 b compared to Earth?
K2-203 b has 1.27 times the radius of Earth.
How long is a year on K2-203 b?
One orbit around K2-203 takes 9.7 Earth days — short enough that 38 of its years would fit into one Earth year.
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