Kepler-68 c
Kepler-68 c is a terrestrial planet orbiting Kepler-68 in the constellation Cygnus. It lies about 470 light-years from Earth and was discovered in 2013 using the transit method.
How Big Is Kepler-68 c?
Kepler-68 c has a radius of 0.98 times that of Earth. Its mass is 1.3 times that of Earth, giving it a density of 7.50 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is Kepler-68 c in the Habitable Zone?
Kepler-68 c orbits inside the inner edge of the habitable zone of Kepler-68. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-68: 0.962–2.261 AU (conservative: 1.218–2.144 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-68 c
The equilibrium temperature of Kepler-68 c is about 1,052 K (779 °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. It receives 204 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-68 c — one full orbit around Kepler-68 — lasts 9.61 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.090 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.10).
How Was Kepler-68 c Discovered?
Kepler-68 c was discovered in 2013 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-68 c?
Kepler-68 c is 470.2 light-years (144.2 parsecs) from Earth. Light arriving here tonight left the planet around the year 1556. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 8,275,520 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-68 c scores 0.30, ranking #1,391 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-68
Kepler-68 c belongs to a system of 2 stars; it orbits Kepler-68.
Kepler-68
- Surface temperature
- 5,847 K (Sun: 5,772 K)
- Mass
- 1.06 M☉
- Radius
- 1.26 R☉
- Age
- 6.8 billion years (Sun: 4.6)
The Kepler-68 Planetary System
Kepler-68 c is one of 4 known planets in the Kepler-68 system. Its siblings:
- Kepler-68 b (Super Earth)
- Kepler-68 d (Cold Gas Giant)
- Kepler-68 e (Cold Gas Giant)
Kepler-68 c — Complete Data
| Radius | 0.979 Earth radii (0.087 Jupiter radii) |
|---|---|
| Mass | 1.30 Earth masses (0.004 Jupiter masses) |
| Density | 7.50 g/cm³ (Earth: 5.51) |
| Orbital period | 9.61 days |
| Orbital distance | 0.090 AU |
| Eccentricity | 0.099 |
| Equilibrium temperature | 1,052 K (779 °C) |
| Stellar irradiation | 204.00× Earth |
| Earth Similarity Index | 0.30 |
| Distance from Earth | 470.2 light-years (144.2 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2013 |
Data: NASA Exoplanet Archive, last updated 2023-04-17. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-68 c
Is Kepler-68 c habitable?
No — Kepler-68 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-68 c?
Kepler-68 c is about 470 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 8,275,520 years to get there.
How big is Kepler-68 c compared to Earth?
Kepler-68 c has 0.98 times the radius of Earth and about 1.3 times its mass.
How long is a year on Kepler-68 c?
One orbit around Kepler-68 takes 9.6 Earth days — short enough that 38 of its years would fit into one Earth year.
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