K2-8 b
K2-8 b is a sub-Neptune orbiting the K3 V star K2-8 in the constellation Leo. It lies about 1,316 light-years from Earth and was discovered in 2015 using the transit method.
How Big Is K2-8 b?
K2-8 b has a radius of 3.58 times that of Earth.
Is K2-8 b in the Habitable Zone?
K2-8 b orbits inside the inner edge of the habitable zone of K2-8. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of K2-8: 0.414–1.007 AU (conservative: 0.525–0.955 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on K2-8 b
The equilibrium temperature of K2-8 b is about 631 K (358 °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 37.70 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on K2-8 b — one full orbit around K2-8 — lasts 10.4 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.086 AU — closer to its star than Mercury is to the Sun.
How Was K2-8 b Discovered?
K2-8 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 K2-8 b?
K2-8 b is 1,316.1 light-years (403.5 parsecs) from Earth. Light arriving here tonight left the planet about 1,316 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 23,163,360 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. K2-8 b scores 0.22, ranking #3,655 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: K2-8
K2-8
- Spectral type
- K3 V
- Surface temperature
- 4,870 K (Sun: 5,772 K)
- Mass
- 0.78 M☉
- Radius
- 0.74 R☉
The K2-8 Planetary System
K2-8 b is one of 2 known planets in the K2-8 system. Its siblings:
- K2-8 c (Mini Neptune)
K2-8 b — Complete Data
| Radius | 3.580 Earth radii (0.319 Jupiter radii) |
|---|---|
| Orbital period | 10.35 days |
| Orbital distance | 0.086 AU |
| Equilibrium temperature | 631 K (358 °C) |
| Stellar irradiation | 37.70× Earth |
| Earth Similarity Index | 0.22 |
| Distance from Earth | 1,316.1 light-years (403.5 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 K2-8 b
Is K2-8 b habitable?
No — K2-8 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is K2-8 b?
K2-8 b is about 1,316 light-years from Earth in the constellation Leo. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 23,163,360 years to get there.
How big is K2-8 b compared to Earth?
K2-8 b has 3.58 times the radius of Earth.
How long is a year on K2-8 b?
One orbit around K2-8 takes 10.4 Earth days — short enough that 35 of its years would fit into one Earth year.
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