Kepler-20 d
Kepler-20 d 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 d?
Kepler-20 d has a radius of 2.61 times that of Earth. Its mass is 13.4 times that of Earth, giving it a density of 4.10 g/cm³ — between that of rocky and gaseous planets.
Is Kepler-20 d in the Habitable Zone?
Kepler-20 d 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 d
The equilibrium temperature of Kepler-20 d is about 430 K (157 °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 5.71 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-20 d — one full orbit around Kepler-20 — lasts 77.6 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.347 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.08).
How Was Kepler-20 d Discovered?
Kepler-20 d 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 d?
Kepler-20 d 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 d scores 0.41, ranking #428 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-20
Kepler-20 d 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 d 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 e (Terrestrial)
- Kepler-20 f (Terrestrial)
- Kepler-20 g (Neptune-like)
Kepler-20 d — Complete Data
| Radius | 2.606 Earth radii (0.232 Jupiter radii) |
|---|---|
| Mass | 13.40 Earth masses (0.042 Jupiter masses) |
| Density | 4.10 g/cm³ (Earth: 5.51) |
| Orbital period | 77.61 days |
| Orbital distance | 0.347 AU |
| Eccentricity | 0.082 |
| Equilibrium temperature | 430 K (157 °C) |
| Stellar irradiation | 5.71× Earth |
| Earth Similarity Index | 0.41 |
| 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 d
Is Kepler-20 d habitable?
No — Kepler-20 d orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-20 d?
Kepler-20 d 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 d compared to Earth?
Kepler-20 d has 2.61 times the radius of Earth and about 13.4 times its mass.
How long is a year on Kepler-20 d?
One orbit around Kepler-20 takes 77.6 Earth days.
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