K2-111 b
K2-111 b is a super-Earth orbiting the G2 star K2-111 in the constellation Taurus. It lies about 654 light-years from Earth and was discovered in 2017 using the transit method.
How Big Is K2-111 b?
K2-111 b has a radius of 1.84 times that of Earth. Its mass is 5.4 times that of Earth, giving it a density of 5.07 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is K2-111 b in the Habitable Zone?
K2-111 b orbits inside the inner edge of the habitable zone of K2-111. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-111: 0.937–2.208 AU (conservative: 1.187–2.094 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-111 b
The equilibrium temperature of K2-111 b is about 1,293 K (1,020 °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 K2-111 b — one full orbit around K2-111 — lasts 5.35 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.057 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.13).
How Was K2-111 b Discovered?
K2-111 b was discovered in 2017 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 K2-111 b?
K2-111 b is 653.6 light-years (200.4 parsecs) from Earth. Light arriving here tonight left the planet around the year 1373. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 11,503,360 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. K2-111 b scores 0.27, ranking #2,719 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-111
K2-111
- Spectral type
- G2
- Surface temperature
- 5,775 K (Sun: 5,772 K)
- Mass
- 0.84 M☉
- Radius
- 1.25 R☉
- Age
- 12.3 billion years (Sun: 4.6)
The K2-111 Planetary System
K2-111 b is one of 2 known planets in the K2-111 system. Its siblings:
- K2-111 c (Neptune-like)
K2-111 b — Complete Data
| Radius | 1.837 Earth radii (0.164 Jupiter radii) |
|---|---|
| Mass | 5.35 Earth masses (0.017 Jupiter masses) |
| Density | 5.07 g/cm³ (Earth: 5.51) |
| Orbital period | 5.35 days |
| Orbital distance | 0.057 AU |
| Eccentricity | 0.134 |
| Equilibrium temperature | 1,293 K (1,020 °C) |
| Earth Similarity Index | 0.27 |
| Distance from Earth | 653.6 light-years (200.4 parsecs) |
| Constellation | Taurus |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2017 |
Data: NASA Exoplanet Archive, last updated 2026-04-16. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-111 b
Is K2-111 b habitable?
No — K2-111 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-111 b?
K2-111 b is about 654 light-years from Earth in the constellation Taurus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 11,503,360 years to get there.
How big is K2-111 b compared to Earth?
K2-111 b has 1.84 times the radius of Earth and about 5.4 times its mass.
How long is a year on K2-111 b?
One orbit around K2-111 takes 5.4 Earth days — short enough that 68 of its years would fit into one Earth year.
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