Kepler-20 g
Kepler-20 g is a Neptune-like planet orbiting Kepler-20 in the constellation Lyra. It lies about 922 light-years from Earth and was discovered in 2016 using the radial velocity method.
Is Kepler-20 g in the Habitable Zone?
Kepler-20 g 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 g
The equilibrium temperature of Kepler-20 g is about 524 K (251 °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.
Orbit and Year Length
A year on Kepler-20 g — one full orbit around Kepler-20 — lasts 34.9 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.206 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.15).
How Was Kepler-20 g Discovered?
Kepler-20 g was discovered in 2016 using the radial velocity method, with observations from Multiple Observatories.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is Kepler-20 g?
Kepler-20 g 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 g scores 0.23, ranking #3,545 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-20
Kepler-20 g 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 g is one of 6 known planets in the Kepler-20 system. Its siblings:
- Kepler-20 b (Super Earth)
- Kepler-20 c (Mini Neptune)
- Kepler-20 d (Super Earth)
- Kepler-20 e (Terrestrial)
- Kepler-20 f (Terrestrial)
Kepler-20 g — Complete Data
| Mass (best estimate) | 19.96 Earth masses |
|---|---|
| Orbital period | 34.94 days |
| Orbital distance | 0.206 AU |
| Eccentricity | 0.150 |
| Equilibrium temperature | 524 K (251 °C) |
| Earth Similarity Index | 0.23 |
| Distance from Earth | 921.6 light-years (282.6 parsecs) |
| Constellation | Lyra |
| Discovery method | Radial Velocity |
| Discovery facility | Multiple Observatories |
| Discovery year | 2016 |
Data: NASA Exoplanet Archive, last updated 2017-03-28. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-20 g
Is Kepler-20 g habitable?
No — Kepler-20 g orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-20 g?
Kepler-20 g 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 long is a year on Kepler-20 g?
One orbit around Kepler-20 takes 34.9 Earth days — short enough that 10 of its years would fit into one Earth year.
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