HD 102117 b
HD 102117 b is a cold gas giant orbiting HD 102117 in the constellation Centaurus. It lies about 129 light-years from Earth and was discovered in 2005 using the radial velocity method.
Is HD 102117 b in the Habitable Zone?
HD 102117 b orbits inside the inner edge of the habitable zone of HD 102117. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HD 102117: 0.891–2.106 AU (conservative: 1.128–1.996 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Orbit and Year Length
A year on HD 102117 b — one full orbit around HD 102117 — lasts 20.8 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.150 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.12).
How Was HD 102117 b Discovered?
HD 102117 b was discovered in 2005 using the radial velocity method, with observations from La Silla Observatory.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is HD 102117 b?
HD 102117 b is 129.1 light-years (39.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1897. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 2,272,160 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. HD 102117 b scores 0.12, ranking #4,344 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 102117
HD 102117
- Surface temperature
- 5,655 K (Sun: 5,772 K)
- Mass
- 1.06 M☉
- Radius
- 1.23 R☉
Planetary System
HD 102117 b is the only planet known to orbit HD 102117 so far.
HD 102117 b — Complete Data
| Mass (best estimate) | 54.03 Earth masses |
|---|---|
| Orbital period | 20.81 days |
| Orbital distance | 0.150 AU |
| Eccentricity | 0.120 |
| Earth Similarity Index | 0.12 |
| Distance from Earth | 129.1 light-years (39.6 parsecs) |
| Constellation | Centaurus |
| Discovery method | Radial Velocity |
| Discovery facility | La Silla Observatory |
| Discovery year | 2005 |
Data: NASA Exoplanet Archive, last updated 2018-09-04. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 102117 b
Is HD 102117 b habitable?
No — HD 102117 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is HD 102117 b?
HD 102117 b is about 129 light-years from Earth in the constellation Centaurus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 2,272,160 years to get there.
How long is a year on HD 102117 b?
One orbit around HD 102117 takes 20.8 Earth days — short enough that 18 of its years would fit into one Earth year.
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