HD 81688 b
HD 81688 b is a cold gas giant orbiting the K0 III-IV star HD 81688 in the constellation Ursa Major. It lies about 280 light-years from Earth and was discovered in 2007 using the radial velocity method.
Is HD 81688 b in the Habitable Zone?
HD 81688 b orbits inside the inner edge of the habitable zone of HD 81688. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HD 81688: 6.139–14.966 AU (conservative: 7.775–14.189 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 81688 b — one full orbit around HD 81688 — lasts 183.9 Earth days, between the years of Mercury (88 days) and Earth (365 days). It orbits at an average distance of 0.648 AU — comparable to the inner Solar System. Its orbit is nearly circular (eccentricity 0.040).
How Was HD 81688 b Discovered?
HD 81688 b was discovered in 2007 using the radial velocity method, with observations from Okayama Astrophysical 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 81688 b?
HD 81688 b is 279.6 light-years (85.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 1747. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 4,920,960 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 81688 b scores 0.07, ranking #4,827 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 81688
HD 81688
- Spectral type
- K0 III-IV
- Surface temperature
- 4,797 K (Sun: 5,772 K)
- Mass
- 1.07 M☉
- Radius
- 11.13 R☉
- Luminosity
- 60.3004 L☉
Planetary System
HD 81688 b is the only planet known to orbit HD 81688 so far.
HD 81688 b — Complete Data
| Mass (best estimate) | 525.69 Earth masses |
|---|---|
| Orbital period | 183.93 days |
| Orbital distance | 0.648 AU |
| Eccentricity | 0.040 |
| Earth Similarity Index | 0.07 |
| Distance from Earth | 279.6 light-years (85.7 parsecs) |
| Constellation | Ursa Major |
| Discovery method | Radial Velocity |
| Discovery facility | Okayama Astrophysical Observatory |
| Discovery year | 2007 |
Data: NASA Exoplanet Archive, last updated 2023-09-19. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 81688 b
Is HD 81688 b habitable?
No — HD 81688 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is HD 81688 b?
HD 81688 b is about 280 light-years from Earth in the constellation Ursa Major. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 4,920,960 years to get there.
How long is a year on HD 81688 b?
One orbit around HD 81688 takes 183.9 Earth days.
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