Kepler-117 c
Kepler-117 c 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 c?
Kepler-117 c has a radius of 12.34 times that of Earth, or 1.10 times the radius of Jupiter. Its mass is 585 times that of Earth, giving it a density of 1.74 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-117 c in the Habitable Zone?
Kepler-117 c 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 c
The equilibrium temperature of Kepler-117 c is about 704 K (431 °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 c — one full orbit around Kepler-117 — lasts 50.8 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.280 AU — closer to its star than Mercury is to the Sun. Its orbit is nearly circular (eccentricity 0.032).
How Was Kepler-117 c Discovered?
Kepler-117 c 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 c?
Kepler-117 c 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 c scores 0.10, ranking #4,475 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 c is one of 2 known planets in the Kepler-117 system. Its siblings:
- Kepler-117 b (Cold Gas Giant)
Kepler-117 c — Complete Data
| Radius | 12.341 Earth radii (1.101 Jupiter radii) |
|---|---|
| Mass | 584.78 Earth masses (1.840 Jupiter masses) |
| Density | 1.74 g/cm³ (Earth: 5.51) |
| Orbital period | 50.79 days |
| Orbital distance | 0.280 AU |
| Eccentricity | 0.032 |
| Equilibrium temperature | 704 K (431 °C) |
| Earth Similarity Index | 0.10 |
| 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 c
Is Kepler-117 c habitable?
No — Kepler-117 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-117 c?
Kepler-117 c 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 c compared to Earth?
Kepler-117 c has 12.34 times the radius of Earth and about 585 times its mass.
How long is a year on Kepler-117 c?
One orbit around Kepler-117 takes 50.8 Earth days.
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