Kepler-39 b
Kepler-39 b is a cold gas giant orbiting the F7 V star Kepler-39 in the constellation Cygnus. It lies about 3,449 light-years from Earth and was discovered in 2011 using the transit method.
How Big Is Kepler-39 b?
Kepler-39 b has a radius of 13.90 times that of Earth, or 1.24 times the radius of Jupiter. Its mass is 6,388 times that of Earth, giving it a density of 13.00 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is Kepler-39 b in the Habitable Zone?
Kepler-39 b orbits inside the inner edge of the habitable zone of Kepler-39. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-39: 1.226–2.852 AU (conservative: 1.552–2.704 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-39 b
The equilibrium temperature of Kepler-39 b is about 897 K (624 °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-39 b — one full orbit around Kepler-39 — lasts 21.1 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.164 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.11).
How Was Kepler-39 b Discovered?
Kepler-39 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-39 b?
Kepler-39 b is 3,448.8 light-years (1,057.4 parsecs) from Earth. Light arriving here tonight left the planet about 3,449 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 60,698,880 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-39 b scores 0.08, ranking #4,729 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-39
Kepler-39
- Spectral type
- F7 V
- Surface temperature
- 6,350 K (Sun: 5,772 K)
- Mass
- 1.29 M☉
- Radius
- 1.40 R☉
- Age
- 2.1 billion years (Sun: 4.6)
Planetary System
Kepler-39 b is the only planet known to orbit Kepler-39 so far.
Kepler-39 b — Complete Data
| Radius | 13.900 Earth radii (1.240 Jupiter radii) |
|---|---|
| Mass | 6,388.10 Earth masses (20.100 Jupiter masses) |
| Density | 13.00 g/cm³ (Earth: 5.51) |
| Orbital period | 21.09 days |
| Orbital distance | 0.164 AU |
| Eccentricity | 0.112 |
| Equilibrium temperature | 897 K (624 °C) |
| Earth Similarity Index | 0.08 |
| Distance from Earth | 3,448.8 light-years (1,057.4 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2011 |
Data: NASA Exoplanet Archive, last updated 2015-01-29. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-39 b
Is Kepler-39 b habitable?
No — Kepler-39 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-39 b?
Kepler-39 b is about 3,449 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 60,698,880 years to get there.
How big is Kepler-39 b compared to Earth?
Kepler-39 b has 13.90 times the radius of Earth and about 6,388 times its mass.
How long is a year on Kepler-39 b?
One orbit around Kepler-39 takes 21.1 Earth days — short enough that 17 of its years would fit into one Earth year.
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