Kepler-42 b
Kepler-42 b is a terrestrial planet orbiting the M star Kepler-42 in the constellation Cygnus. It lies about 131 light-years from Earth and was discovered in 2011 using the transit method.
How Big Is Kepler-42 b?
Kepler-42 b has a radius of 0.78 times that of Earth.
Is Kepler-42 b in the Habitable Zone?
Kepler-42 b orbits inside the inner edge of the habitable zone of Kepler-42. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-42: 0.040–0.107 AU (conservative: 0.051–0.101 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-42 b
The equilibrium temperature of Kepler-42 b is about 519 K (246 °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.
Orbit and Year Length
A year on Kepler-42 b — one full orbit around Kepler-42 — lasts just 29.1 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.012 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-42 b Discovered?
Kepler-42 b was discovered in 2011 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-42 b?
Kepler-42 b is 130.7 light-years (40.1 parsecs) from Earth. Light arriving here tonight left the planet around the year 1896. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 2,300,320 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-42 b scores 0.36, ranking #682 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-42
Kepler-42
- Spectral type
- M
- Surface temperature
- 3,068 K (Sun: 5,772 K)
- Mass
- 0.13 M☉
- Radius
- 0.17 R☉
- Luminosity
- 0.0024 L☉
- Age
- 4.5 billion years (Sun: 4.6)
The Kepler-42 Planetary System
Kepler-42 b is one of 3 known planets in the Kepler-42 system. Its siblings:
- Kepler-42 c (Terrestrial)
- Kepler-42 d (Terrestrial)
Kepler-42 b — Complete Data
| Radius | 0.780 Earth radii (0.070 Jupiter radii) |
|---|---|
| Orbital period | 1.21 days |
| Orbital distance | 0.012 AU |
| Equilibrium temperature | 519 K (246 °C) |
| Earth Similarity Index | 0.36 |
| Distance from Earth | 130.7 light-years (40.1 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2011 |
Data: NASA Exoplanet Archive, last updated 2014-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-42 b
Is Kepler-42 b habitable?
No — Kepler-42 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-42 b?
Kepler-42 b is about 131 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 2,300,320 years to get there.
How big is Kepler-42 b compared to Earth?
Kepler-42 b has 0.78 times the radius of Earth.
How long is a year on Kepler-42 b?
One orbit around Kepler-42 takes 1.2 Earth days — short enough that 301 of its years would fit into one Earth year.
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