Gl 378 b
Gl 378 b is a Neptune-like planet orbiting the M1 star Gl 378 in the constellation Ursa Major. It lies about 49 light-years from Earth and was discovered in 2019 using the radial velocity method.
Is Gl 378 b in the Habitable Zone?
Gl 378 b orbits inside the inner edge of the habitable zone of Gl 378. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Gl 378: 0.199–0.507 AU (conservative: 0.252–0.481 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Gl 378 b
The equilibrium temperature of Gl 378 b is about 830 K (557 °C) — hot enough to melt many metals. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C.
Orbit and Year Length
A year on Gl 378 b — one full orbit around Gl 378 — lasts 3.82 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.039 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.11).
How Was Gl 378 b Discovered?
Gl 378 b was discovered in 2019 using the radial velocity method, with observations from Haute-Provence 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 Gl 378 b?
Gl 378 b is 48.8 light-years (15.0 parsecs) from Earth. Light arriving here tonight left the planet around the year 1978. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 858,880 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. Gl 378 b scores 0.22, ranking #3,700 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Gl 378
Gl 378
- Spectral type
- M1
- Surface temperature
- 3,879 K (Sun: 5,772 K)
- Mass
- 0.56 M☉
- Radius
- 0.56 R☉
- Luminosity
- 0.0600 L☉
Planetary System
Gl 378 b is the only planet known to orbit Gl 378 so far.
Gl 378 b — Complete Data
| Mass (best estimate) | 13.02 Earth masses |
|---|---|
| Orbital period | 3.82 days |
| Orbital distance | 0.039 AU |
| Eccentricity | 0.109 |
| Equilibrium temperature | 830 K (557 °C) |
| Earth Similarity Index | 0.22 |
| Distance from Earth | 48.8 light-years (15.0 parsecs) |
| Constellation | Ursa Major |
| Discovery method | Radial Velocity |
| Discovery facility | Haute-Provence Observatory |
| Discovery year | 2019 |
Data: NASA Exoplanet Archive, last updated 2019-03-01. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Gl 378 b
Is Gl 378 b habitable?
No — Gl 378 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Gl 378 b?
Gl 378 b is about 49 light-years from Earth in the constellation Ursa Major. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 858,880 years to get there.
How long is a year on Gl 378 b?
One orbit around Gl 378 takes 3.8 Earth days — short enough that 96 of its years would fit into one Earth year.
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