HD 99109 b
HD 99109 b is a cold gas giant orbiting HD 99109 in the constellation Leo. It lies about 179 light-years from Earth and was discovered in 2005 using the radial velocity method. It orbits within the habitable zone of its star — the region where liquid water could exist on a planet's surface.
Is HD 99109 b in the Habitable Zone?
HD 99109 b orbits inside the conservative habitable zone of HD 99109 — the region where a rocky planet could sustain liquid water on its surface. This makes it one of the most interesting known exoplanets in the search for life.
Habitable zone of HD 99109: 0.632–1.513 AU (conservative: 0.801–1.434 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 HD 99109 b — one full orbit around HD 99109 — lasts 439.3 Earth days, longer than an Earth year. It orbits at an average distance of 1.110 AU. Its orbit is mildly elliptical (eccentricity 0.09).
How Was HD 99109 b Discovered?
HD 99109 b was discovered in 2005 using the radial velocity method, with observations from W. M. Keck 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 99109 b?
HD 99109 b is 178.7 light-years (54.8 parsecs) from Earth. Light arriving here tonight left the planet around the year 1848. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,145,120 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. HD 99109 b scores 0.35, ranking #757 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 99109
HD 99109
- Surface temperature
- 5,282 K (Sun: 5,772 K)
- Mass
- 0.76 M☉
- Radius
- 0.98 R☉
Planetary System
HD 99109 b is the only planet known to orbit HD 99109 so far.
HD 99109 b — Complete Data
| Mass (best estimate) | 139.85 Earth masses |
|---|---|
| Orbital period | 439.30 days |
| Orbital distance | 1.110 AU |
| Eccentricity | 0.090 |
| Earth Similarity Index | 0.35 |
| Distance from Earth | 178.7 light-years (54.8 parsecs) |
| Constellation | Leo |
| Discovery method | Radial Velocity |
| Discovery facility | W. M. Keck Observatory |
| Discovery year | 2005 |
Data: NASA Exoplanet Archive, last updated 2018-09-04. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 99109 b
Is HD 99109 b habitable?
HD 99109 b orbits within the habitable zone of HD 99109, the region where liquid water could exist on a planet's surface. It sits in the conservative habitable zone — the most promising region for habitability. Whether it is actually habitable depends on its atmosphere and composition, which remain unknown.
How far away is HD 99109 b?
HD 99109 b is about 179 light-years from Earth in the constellation Leo. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,145,120 years to get there.
How long is a year on HD 99109 b?
One orbit around HD 99109 takes 439.3 Earth days.
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