Kepler-9 b
Kepler-9 b is a cold gas giant orbiting Kepler-9 in the constellation Lyra. It lies about 2,049 light-years from Earth and was discovered in 2010 using the transit method.
How Big Is Kepler-9 b?
Kepler-9 b has a radius of 8.29 times that of Earth, or 0.74 times the radius of Jupiter. Its mass is 43.4 times that of Earth, giving it a density of 0.42 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-9 b in the Habitable Zone?
Kepler-9 b orbits inside the inner edge of the habitable zone of Kepler-9. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-9: 0.765–1.803 AU (conservative: 0.969–1.709 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 ›
Orbit and Year Length
A year on Kepler-9 b — one full orbit around Kepler-9 — lasts 19.2 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.143 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.06).
How Was Kepler-9 b Discovered?
Kepler-9 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-9 b?
Kepler-9 b is 2,049.1 light-years (628.3 parsecs) from Earth. Light arriving here tonight left the planet about 2,049 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 36,064,160 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-9 b scores 0.13, ranking #4,309 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-9
Kepler-9
- Surface temperature
- 5,777 K (Sun: 5,772 K)
- Mass
- 1.07 M☉
- Radius
- 1.02 R☉
- Age
- 1.0 billion years (Sun: 4.6)
The Kepler-9 Planetary System
Kepler-9 b is one of 3 known planets in the Kepler-9 system. Its siblings:
- Kepler-9 c (Cold Gas Giant)
- Kepler-9 d (Lava World)
Kepler-9 b — Complete Data
| Radius | 8.290 Earth radii (0.740 Jupiter radii) |
|---|---|
| Mass | 43.40 Earth masses (0.137 Jupiter masses) |
| Density | 0.42 g/cm³ (Earth: 5.51) |
| Orbital period | 19.24 days |
| Orbital distance | 0.143 AU |
| Eccentricity | 0.061 |
| Earth Similarity Index | 0.13 |
| Distance from Earth | 2,049.1 light-years (628.3 parsecs) |
| Constellation | Lyra |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2010 |
Data: NASA Exoplanet Archive, last updated 2019-07-08. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-9 b
Is Kepler-9 b habitable?
No — Kepler-9 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-9 b?
Kepler-9 b is about 2,049 light-years from Earth in the constellation Lyra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 36,064,160 years to get there.
How big is Kepler-9 b compared to Earth?
Kepler-9 b has 8.29 times the radius of Earth and about 43.4 times its mass.
How long is a year on Kepler-9 b?
One orbit around Kepler-9 takes 19.2 Earth days — short enough that 19 of its years would fit into one Earth year.
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