GJ 685 b
GJ 685 b is a super-Earth orbiting the M0.5 star GJ 685 in the constellation Draco. It lies about 47 light-years from Earth and was discovered in 2019 using the radial velocity method.
Is GJ 685 b in the Habitable Zone?
GJ 685 b orbits inside the inner edge of the habitable zone of GJ 685. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of GJ 685: 0.192–0.491 AU (conservative: 0.244–0.466 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Orbit and Year Length
A year on GJ 685 b — one full orbit around GJ 685 — lasts 24.2 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.134 AU — closer to its star than Mercury is to the Sun.
How Was GJ 685 b Discovered?
GJ 685 b was discovered in 2019 using the radial velocity method, with observations from Roque de los Muchachos 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 GJ 685 b?
GJ 685 b is 46.7 light-years (14.3 parsecs) from Earth. Light arriving here tonight left the planet around the year 1980. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 821,920 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. GJ 685 b scores 0.50, ranking #254 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: GJ 685
GJ 685
- Spectral type
- M0.5
- Surface temperature
- 3,816 K (Sun: 5,772 K)
- Mass
- 0.55 M☉
- Radius
- 0.54 R☉
- Luminosity
- 0.0558 L☉
Planetary System
GJ 685 b is the only planet known to orbit GJ 685 so far.
GJ 685 b — Complete Data
| Mass (best estimate) | 9.00 Earth masses |
|---|---|
| Orbital period | 24.16 days |
| Orbital distance | 0.134 AU |
| Earth Similarity Index | 0.50 |
| Distance from Earth | 46.7 light-years (14.3 parsecs) |
| Constellation | Draco |
| Discovery method | Radial Velocity |
| Discovery facility | Roque de los Muchachos Observatory |
| Discovery year | 2019 |
Data: NASA Exoplanet Archive, last updated 2019-04-08. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 685 b
Is GJ 685 b habitable?
No — GJ 685 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is GJ 685 b?
GJ 685 b is about 47 light-years from Earth in the constellation Draco. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 821,920 years to get there.
How long is a year on GJ 685 b?
One orbit around GJ 685 takes 24.2 Earth days — short enough that 15 of its years would fit into one Earth year.
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