Kepler-278 c
Kepler-278 c is a super-Earth orbiting the K2 III-IV star Kepler-278 in the constellation Lyra. It lies about 1,445 light-years from Earth and was discovered in 2014 using the transit method.
How Big Is Kepler-278 c?
Kepler-278 c has a radius of 3.27 times that of Earth. Its mass is 34.9 times that of Earth, giving it a density of 5.50 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is Kepler-278 c in the Habitable Zone?
Kepler-278 c orbits inside the inner edge of the habitable zone of Kepler-278. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-278: 1.657–4.012 AU (conservative: 2.099–3.803 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-278 c
The equilibrium temperature of Kepler-278 c is about 492 K (219 °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 54.30 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-278 c — one full orbit around Kepler-278 — lasts 51.1 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.287 AU — closer to its star than Mercury is to the Sun. Its orbit is highly elliptical (eccentricity 0.62), swinging dramatically closer to and farther from its star.
How Was Kepler-278 c Discovered?
Kepler-278 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-278 c?
Kepler-278 c is 1,445.0 light-years (443.0 parsecs) from Earth. Light arriving here tonight left the planet about 1,445 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 25,432,000 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-278 c scores 0.21, ranking #3,778 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-278
Kepler-278
- Spectral type
- K2 III-IV
- Surface temperature
- 4,965 K (Sun: 5,772 K)
- Mass
- 1.23 M☉
- Radius
- 2.86 R☉
- Luminosity
- 4.4600 L☉
- Age
- 5.8 billion years (Sun: 4.6)
The Kepler-278 Planetary System
Kepler-278 c is one of 2 known planets in the Kepler-278 system. Its siblings:
- Kepler-278 b (Super Earth)
Kepler-278 c — Complete Data
| Radius | 3.268 Earth radii (0.292 Jupiter radii) |
|---|---|
| Mass | 34.90 Earth masses (0.110 Jupiter masses) |
| Density | 5.50 g/cm³ (Earth: 5.51) |
| Orbital period | 51.11 days |
| Orbital distance | 0.287 AU |
| Eccentricity | 0.616 |
| Equilibrium temperature | 492 K (219 °C) |
| Stellar irradiation | 54.30× Earth |
| Earth Similarity Index | 0.21 |
| Distance from Earth | 1,445.0 light-years (443.0 parsecs) |
| Constellation | Lyra |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2014 |
Data: NASA Exoplanet Archive, last updated 2025-09-17. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-278 c
Is Kepler-278 c habitable?
No — Kepler-278 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-278 c?
Kepler-278 c is about 1,445 light-years from Earth in the constellation Lyra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 25,432,000 years to get there.
How big is Kepler-278 c compared to Earth?
Kepler-278 c has 3.27 times the radius of Earth and about 34.9 times its mass.
How long is a year on Kepler-278 c?
One orbit around Kepler-278 takes 51.1 Earth days.
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