K2-157 b
K2-157 b is a lava world orbiting the G9 V star K2-157 in the constellation Virgo. It lies about 973 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is K2-157 b?
K2-157 b has a radius of 0.94 times that of Earth. Its mass is 1.1 times that of Earth, giving it a density of 7.70 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is K2-157 b in the Habitable Zone?
K2-157 b orbits inside the inner edge of the habitable zone of K2-157. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-157: 0.564–1.348 AU (conservative: 0.715–1.278 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-157 b
The equilibrium temperature of K2-157 b is about 2,432 K (2,159 °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 6,660 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-157 b — one full orbit around K2-157 — lasts just 8.8 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.010 AU — closer to its star than Mercury is to the Sun.
How Was K2-157 b Discovered?
K2-157 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 K2-157 b?
K2-157 b is 973.2 light-years (298.4 parsecs) from Earth. Light arriving here tonight left the planet around the year 1053. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 17,128,320 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. K2-157 b scores 0.29, ranking #1,668 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-157
K2-157
- Spectral type
- G9 V
- Surface temperature
- 5,334 K (Sun: 5,772 K)
- Mass
- 0.89 M☉
- Radius
- 0.86 R☉
- Age
- 8.8 billion years (Sun: 4.6)
The K2-157 Planetary System
K2-157 b is one of 3 known planets in the K2-157 system. Its siblings:
K2-157 b — Complete Data
| Radius | 0.935 Earth radii (0.083 Jupiter radii) |
|---|---|
| Mass | 1.14 Earth masses (0.004 Jupiter masses) |
| Density | 7.70 g/cm³ (Earth: 5.51) |
| Orbital period | 0.37 days |
| Orbital distance | 0.010 AU |
| Equilibrium temperature | 2,432 K (2,159 °C) |
| Stellar irradiation | 6,660.00× Earth |
| Earth Similarity Index | 0.29 |
| Distance from Earth | 973.2 light-years (298.4 parsecs) |
| Constellation | Virgo |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2025-05-13. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-157 b
Is K2-157 b habitable?
No — K2-157 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-157 b?
K2-157 b is about 973 light-years from Earth in the constellation Virgo. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 17,128,320 years to get there.
How big is K2-157 b compared to Earth?
K2-157 b has 0.94 times the radius of Earth and about 1.1 times its mass.
How long is a year on K2-157 b?
One orbit around K2-157 takes 0.4 Earth days — short enough that 1,000 of its years would fit into one Earth year.
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