Kepler-91 b
Kepler-91 b is a hot Jupiter orbiting Kepler-91 in the constellation Lyra. It lies about 4,223 light-years from Earth and was discovered in 2013 using the transit method.
How Big Is Kepler-91 b?
Kepler-91 b has a radius of 15.32 times that of Earth, or 1.37 times the radius of Jupiter. Its mass is 257 times that of Earth, giving it a density of 0.40 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-91 b in the Habitable Zone?
Kepler-91 b orbits inside the inner edge of the habitable zone of Kepler-91. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-91: 3.119–7.687 AU (conservative: 3.950–7.288 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-91 b
The equilibrium temperature of Kepler-91 b is about 2,040 K (1,767 °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-91 b — one full orbit around Kepler-91 — lasts 6.25 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.073 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-91 b Discovered?
Kepler-91 b 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-91 b?
Kepler-91 b is 4,222.7 light-years (1,294.7 parsecs) from Earth. Light arriving here tonight left the planet about 4,223 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 74,319,520 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-91 b scores 0.06, ranking #5,152 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-91
Kepler-91
- Surface temperature
- 4,550 K (Sun: 5,772 K)
- Mass
- 1.31 M☉
- Radius
- 6.30 R☉
Planetary System
Kepler-91 b is the only planet known to orbit Kepler-91 so far.
Kepler-91 b — Complete Data
| Radius | 15.323 Earth radii (1.367 Jupiter radii) |
|---|---|
| Mass | 257.44 Earth masses (0.810 Jupiter masses) |
| Density | 0.40 g/cm³ (Earth: 5.51) |
| Orbital period | 6.25 days |
| Orbital distance | 0.073 AU |
| Equilibrium temperature | 2,040 K (1,767 °C) |
| Earth Similarity Index | 0.06 |
| Distance from Earth | 4,222.7 light-years (1,294.7 parsecs) |
| Constellation | Lyra |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2013 |
Data: NASA Exoplanet Archive, last updated 2015-10-07. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-91 b
Is Kepler-91 b habitable?
No — Kepler-91 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-91 b?
Kepler-91 b is about 4,223 light-years from Earth in the constellation Lyra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 74,319,520 years to get there.
How big is Kepler-91 b compared to Earth?
Kepler-91 b has 15.32 times the radius of Earth and about 257 times its mass.
How long is a year on Kepler-91 b?
One orbit around Kepler-91 takes 6.2 Earth days — short enough that 58 of its years would fit into one Earth year.
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