Kepler-20 b
Kepler-20 b is a super-Earth orbiting Kepler-20 in the constellation Lyra. It lies about 922 light-years from Earth and was discovered in 2011 using the transit method.
How Big Is Kepler-20 b?
Kepler-20 b has a radius of 1.77 times that of Earth. Its mass is 9.7 times that of Earth, giving it a density of 9.40 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is Kepler-20 b in the Habitable Zone?
Kepler-20 b orbits inside the inner edge of the habitable zone of Kepler-20. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-20: 0.632–1.502 AU (conservative: 0.801–1.424 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-20 b
The equilibrium temperature of Kepler-20 b is about 1,187 K (914 °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 331 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-20 b — one full orbit around Kepler-20 — lasts 3.70 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.046 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.08).
How Was Kepler-20 b Discovered?
Kepler-20 b was discovered in 2011 using the transit method, with observations from Kepler.
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 Kepler-20 b?
Kepler-20 b is 921.6 light-years (282.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1105. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 16,220,160 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. Kepler-20 b scores 0.27, ranking #2,614 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-20
Kepler-20 b belongs to a system of 2 stars; it orbits Kepler-20.
Kepler-20
- Surface temperature
- 5,495 K (Sun: 5,772 K)
- Mass
- 0.93 M☉
- Radius
- 0.92 R☉
- Age
- 5.6 billion years (Sun: 4.6)
The Kepler-20 Planetary System
Kepler-20 b is one of 6 known planets in the Kepler-20 system. Its siblings:
- Kepler-20 c (Mini Neptune)
- Kepler-20 d (Super Earth)
- Kepler-20 e (Terrestrial)
- Kepler-20 f (Terrestrial)
- Kepler-20 g (Neptune-like)
Kepler-20 b — Complete Data
| Radius | 1.773 Earth radii (0.158 Jupiter radii) |
|---|---|
| Mass | 9.70 Earth masses (0.031 Jupiter masses) |
| Density | 9.40 g/cm³ (Earth: 5.51) |
| Orbital period | 3.70 days |
| Orbital distance | 0.046 AU |
| Eccentricity | 0.083 |
| Equilibrium temperature | 1,187 K (914 °C) |
| Stellar irradiation | 331.00× Earth |
| Earth Similarity Index | 0.27 |
| Distance from Earth | 921.6 light-years (282.6 parsecs) |
| Constellation | Lyra |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2011 |
Data: NASA Exoplanet Archive, last updated 2023-04-17. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-20 b
Is Kepler-20 b habitable?
No — Kepler-20 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-20 b?
Kepler-20 b is about 922 light-years from Earth in the constellation Lyra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 16,220,160 years to get there.
How big is Kepler-20 b compared to Earth?
Kepler-20 b has 1.77 times the radius of Earth and about 9.7 times its mass.
How long is a year on Kepler-20 b?
One orbit around Kepler-20 takes 3.7 Earth days — short enough that 99 of its years would fit into one Earth year.
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