Kepler-278 b
Kepler-278 b 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 b?
Kepler-278 b has a radius of 3.96 times that of Earth. Its mass is 56.0 times that of Earth, giving it a density of 5.00 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is Kepler-278 b in the Habitable Zone?
Kepler-278 b 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 b
The equilibrium temperature of Kepler-278 b is about 586 K (313 °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 110 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-278 b — one full orbit around Kepler-278 — lasts 30.2 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.202 AU — closer to its star than Mercury is to the Sun. Its orbit is highly elliptical (eccentricity 0.70), swinging dramatically closer to and farther from its star.
How Was Kepler-278 b Discovered?
Kepler-278 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-278 b?
Kepler-278 b 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 b scores 0.19, ranking #4,006 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 b is one of 2 known planets in the Kepler-278 system. Its siblings:
- Kepler-278 c (Super Earth)
Kepler-278 b — Complete Data
| Radius | 3.955 Earth radii (0.353 Jupiter radii) |
|---|---|
| Mass | 56.00 Earth masses (0.176 Jupiter masses) |
| Density | 5.00 g/cm³ (Earth: 5.51) |
| Orbital period | 30.16 days |
| Orbital distance | 0.202 AU |
| Eccentricity | 0.696 |
| Equilibrium temperature | 586 K (313 °C) |
| Stellar irradiation | 110.00× Earth |
| Earth Similarity Index | 0.19 |
| 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 b
Is Kepler-278 b habitable?
No — Kepler-278 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-278 b?
Kepler-278 b 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 b compared to Earth?
Kepler-278 b has 3.96 times the radius of Earth and about 56.0 times its mass.
How long is a year on Kepler-278 b?
One orbit around Kepler-278 takes 30.2 Earth days — short enough that 12 of its years would fit into one Earth year.
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