K2-5 b
K2-5 b is a super-Earth orbiting the K7.5 V star K2-5 in the constellation Leo. It lies about 662 light-years from Earth and was discovered in 2015 using the transit method.
How Big Is K2-5 b?
K2-5 b has a radius of 1.91 times that of Earth.
Is K2-5 b in the Habitable Zone?
K2-5 b orbits inside the inner edge of the habitable zone of K2-5. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-5: 0.214–0.544 AU (conservative: 0.271–0.516 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-5 b
The equilibrium temperature of K2-5 b is about 565 K (292 °C) — hotter than anywhere on Earth. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 24.10 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-5 b — one full orbit around K2-5 — lasts 5.74 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.053 AU — closer to its star than Mercury is to the Sun.
How Was K2-5 b Discovered?
K2-5 b was discovered in 2015 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 K2-5 b?
K2-5 b is 661.9 light-years (202.9 parsecs) from Earth. Light arriving here tonight left the planet around the year 1365. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 11,649,440 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. K2-5 b scores 0.30, ranking #1,273 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-5
K2-5
- Spectral type
- K7.5 V
- Surface temperature
- 3,930 K (Sun: 5,772 K)
- Mass
- 0.61 M☉
- Radius
- 0.57 R☉
The K2-5 Planetary System
K2-5 b is one of 2 known planets in the K2-5 system. Its siblings:
- K2-5 c (Mini Neptune)
K2-5 b — Complete Data
| Radius | 1.910 Earth radii (0.170 Jupiter radii) |
|---|---|
| Orbital period | 5.74 days |
| Orbital distance | 0.053 AU |
| Equilibrium temperature | 565 K (292 °C) |
| Stellar irradiation | 24.10× Earth |
| Earth Similarity Index | 0.30 |
| Distance from Earth | 661.9 light-years (202.9 parsecs) |
| Constellation | Leo |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2015 |
Data: NASA Exoplanet Archive, last updated 2016-07-06. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About K2-5 b
Is K2-5 b habitable?
No — K2-5 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-5 b?
K2-5 b is about 662 light-years from Earth in the constellation Leo. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 11,649,440 years to get there.
How big is K2-5 b compared to Earth?
K2-5 b has 1.91 times the radius of Earth.
How long is a year on K2-5 b?
One orbit around K2-5 takes 5.7 Earth days — short enough that 64 of its years would fit into one Earth year.
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