Kepler-117 b
Kepler-117 b is a cold gas giant orbiting the F8 V star Kepler-117 in the constellation Cygnus. It lies about 4,747 light-years from Earth and was discovered in 2014 using the transit method.
How Big Is Kepler-117 b?
Kepler-117 b has a radius of 8.06 times that of Earth, or 0.72 times the radius of Jupiter. Its mass is 29.9 times that of Earth, giving it a density of 0.30 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-117 b in the Habitable Zone?
Kepler-117 b orbits inside the inner edge of the habitable zone of Kepler-117. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-117: 1.335–3.118 AU (conservative: 1.691–2.956 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-117 b
The equilibrium temperature of Kepler-117 b is about 984 K (711 °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.
Orbit and Year Length
A year on Kepler-117 b — one full orbit around Kepler-117 — lasts 18.8 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.145 AU — closer to its star than Mercury is to the Sun. Its orbit is nearly circular (eccentricity 0.049).
How Was Kepler-117 b Discovered?
Kepler-117 b was discovered in 2014 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-117 b?
Kepler-117 b is 4,747.4 light-years (1,455.6 parsecs) from Earth. Light arriving here tonight left the planet about 4,747 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 83,554,240 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-117 b scores 0.11, ranking #4,372 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-117
Kepler-117
- Spectral type
- F8 V
- Surface temperature
- 6,150 K (Sun: 5,772 K)
- Mass
- 1.13 M☉
- Radius
- 1.61 R☉
- Age
- 5.3 billion years (Sun: 4.6)
The Kepler-117 Planetary System
Kepler-117 b is one of 2 known planets in the Kepler-117 system. Its siblings:
- Kepler-117 c (Cold Gas Giant)
Kepler-117 b — Complete Data
| Radius | 8.059 Earth radii (0.719 Jupiter radii) |
|---|---|
| Mass | 29.88 Earth masses (0.094 Jupiter masses) |
| Density | 0.30 g/cm³ (Earth: 5.51) |
| Orbital period | 18.80 days |
| Orbital distance | 0.145 AU |
| Eccentricity | 0.049 |
| Equilibrium temperature | 984 K (711 °C) |
| Earth Similarity Index | 0.11 |
| Distance from Earth | 4,747.4 light-years (1,455.6 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2014 |
Data: NASA Exoplanet Archive, last updated 2014-11-19. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-117 b
Is Kepler-117 b habitable?
No — Kepler-117 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-117 b?
Kepler-117 b is about 4,747 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 83,554,240 years to get there.
How big is Kepler-117 b compared to Earth?
Kepler-117 b has 8.06 times the radius of Earth and about 29.9 times its mass.
How long is a year on Kepler-117 b?
One orbit around Kepler-117 takes 18.8 Earth days — short enough that 19 of its years would fit into one Earth year.
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