Kepler-87 b
Kepler-87 b is a cold gas giant orbiting Kepler-87 in the constellation Cygnus. It lies about 4,021 light-years from Earth and was discovered in 2013 using the transit method.
How Big Is Kepler-87 b?
Kepler-87 b has a radius of 13.49 times that of Earth, or 1.20 times the radius of Jupiter. Its mass is 324 times that of Earth, giving it a density of 0.73 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-87 b in the Habitable Zone?
Kepler-87 b orbits inside the inner edge of the habitable zone of Kepler-87. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-87: 1.297–3.070 AU (conservative: 1.642–2.911 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-87 b
The equilibrium temperature of Kepler-87 b is about 478 K (205 °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-87 b — one full orbit around Kepler-87 — lasts 114.7 Earth days, between the years of Mercury (88 days) and Earth (365 days). It orbits at an average distance of 0.481 AU — comparable to the inner Solar System. Its orbit is nearly circular (eccentricity 0.036).
How Was Kepler-87 b Discovered?
Kepler-87 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-87 b?
Kepler-87 b is 4,021.2 light-years (1,232.9 parsecs) from Earth. Light arriving here tonight left the planet about 4,021 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 70,773,120 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-87 b scores 0.17, ranking #4,105 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-87
Kepler-87
- Surface temperature
- 5,600 K (Sun: 5,772 K)
- Mass
- 1.10 M☉
- Radius
- 1.82 R☉
- Age
- 7.5 billion years (Sun: 4.6)
The Kepler-87 Planetary System
Kepler-87 b is one of 2 known planets in the Kepler-87 system. Its siblings:
- Kepler-87 c (Cold Gas Giant)
Kepler-87 b — Complete Data
| Radius | 13.490 Earth radii (1.204 Jupiter radii) |
|---|---|
| Mass | 324.20 Earth masses (1.020 Jupiter masses) |
| Density | 0.73 g/cm³ (Earth: 5.51) |
| Orbital period | 114.74 days |
| Orbital distance | 0.481 AU |
| Eccentricity | 0.036 |
| Equilibrium temperature | 478 K (205 °C) |
| Earth Similarity Index | 0.17 |
| Distance from Earth | 4,021.2 light-years (1,232.9 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2013 |
Data: NASA Exoplanet Archive, last updated 2014-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-87 b
Is Kepler-87 b habitable?
No — Kepler-87 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-87 b?
Kepler-87 b is about 4,021 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 70,773,120 years to get there.
How big is Kepler-87 b compared to Earth?
Kepler-87 b has 13.49 times the radius of Earth and about 324 times its mass.
How long is a year on Kepler-87 b?
One orbit around Kepler-87 takes 114.7 Earth days.
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