Kepler-8 b
Kepler-8 b is a hot Jupiter orbiting Kepler-8 in the constellation Lyra. It lies about 3,333 light-years from Earth and was discovered in 2010 using the transit method.
How Big Is Kepler-8 b?
Kepler-8 b has a radius of 15.87 times that of Earth, or 1.42 times the radius of Jupiter. Its mass is 188 times that of Earth, giving it a density of 0.27 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-8 b in the Habitable Zone?
Kepler-8 b orbits inside the inner edge of the habitable zone of Kepler-8. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-8: 1.256–2.929 AU (conservative: 1.591–2.777 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Temperature on Kepler-8 b
The equilibrium temperature of Kepler-8 b is about 1,680 K (1,407 °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-8 b — one full orbit around Kepler-8 — lasts 3.52 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.047 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-8 b Discovered?
Kepler-8 b was discovered in 2010 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-8 b?
Kepler-8 b is 3,332.9 light-years (1,021.9 parsecs) from Earth. Light arriving here tonight left the planet about 3,333 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 58,659,040 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-8 b scores 0.06, ranking #5,183 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-8
Kepler-8
- Surface temperature
- 6,213 K (Sun: 5,772 K)
- Mass
- 1.21 M☉
- Radius
- 1.49 R☉
Planetary System
Kepler-8 b is the only planet known to orbit Kepler-8 so far.
Kepler-8 b — Complete Data
| Radius | 15.872 Earth radii (1.416 Jupiter radii) |
|---|---|
| Mass | 187.52 Earth masses (0.590 Jupiter masses) |
| Density | 0.27 g/cm³ (Earth: 5.51) |
| Orbital period | 3.52 days |
| Orbital distance | 0.047 AU |
| Equilibrium temperature | 1,680 K (1,407 °C) |
| Earth Similarity Index | 0.06 |
| Distance from Earth | 3,332.9 light-years (1,021.9 parsecs) |
| Constellation | Lyra |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2010 |
Data: NASA Exoplanet Archive, last updated 2015-10-07. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-8 b
Is Kepler-8 b habitable?
No — Kepler-8 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-8 b?
Kepler-8 b is about 3,333 light-years from Earth in the constellation Lyra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 58,659,040 years to get there.
How big is Kepler-8 b compared to Earth?
Kepler-8 b has 15.87 times the radius of Earth and about 188 times its mass.
How long is a year on Kepler-8 b?
One orbit around Kepler-8 takes 3.5 Earth days — short enough that 104 of its years would fit into one Earth year.
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