Kepler-31 b
Kepler-31 b is a Neptune-like planet orbiting Kepler-31 in the constellation Cygnus. It lies about 5,429 light-years from Earth and was discovered in 2011 using the transit method.
How Big Is Kepler-31 b?
Kepler-31 b has a radius of 5.50 times that of Earth.
Is Kepler-31 b in the Habitable Zone?
Kepler-31 b orbits inside the inner edge of the habitable zone of Kepler-31. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-31: 1.065–2.479 AU (conservative: 1.349–2.351 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Orbit and Year Length
A year on Kepler-31 b — one full orbit around Kepler-31 — lasts 20.9 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.160 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-31 b Discovered?
Kepler-31 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-31 b?
Kepler-31 b is 5,429.3 light-years (1,664.6 parsecs) from Earth. Light arriving here tonight left the planet about 5,429 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 95,555,680 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-31 b scores 0.15, ranking #4,187 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-31
Kepler-31
- Surface temperature
- 6,340 K (Sun: 5,772 K)
- Mass
- 1.21 M☉
- Radius
- 1.22 R☉
The Kepler-31 Planetary System
Kepler-31 b is one of 3 known planets in the Kepler-31 system. Its siblings:
- Kepler-31 c (Neptune-like)
- Kepler-31 d (Super Earth)
Kepler-31 b — Complete Data
| Radius | 5.500 Earth radii (0.491 Jupiter radii) |
|---|---|
| Orbital period | 20.86 days |
| Orbital distance | 0.160 AU |
| Earth Similarity Index | 0.15 |
| Distance from Earth | 5,429.3 light-years (1,664.6 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2011 |
Data: NASA Exoplanet Archive, last updated 2014-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-31 b
Is Kepler-31 b habitable?
No — Kepler-31 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-31 b?
Kepler-31 b is about 5,429 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 95,555,680 years to get there.
How big is Kepler-31 b compared to Earth?
Kepler-31 b has 5.50 times the radius of Earth.
How long is a year on Kepler-31 b?
One orbit around Kepler-31 takes 20.9 Earth days — short enough that 18 of its years would fit into one Earth year.
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