GJ 3138 d
GJ 3138 d is a Neptune-like planet orbiting the M0 star GJ 3138 in the constellation Cetus. It lies about 93 light-years from Earth and was discovered in 2017 using the radial velocity method.
Is GJ 3138 d in the Habitable Zone?
GJ 3138 d orbits beyond the outer edge of the habitable zone of GJ 3138. At that distance, any surface water would almost certainly be frozen.
Habitable zone of GJ 3138: 0.173–0.444 AU (conservative: 0.219–0.421 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on GJ 3138 d
GJ 3138 d receives 0.10 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on GJ 3138 d — one full orbit around GJ 3138 — lasts 257.8 Earth days, between the years of Mercury (88 days) and Earth (365 days). It orbits at an average distance of 0.698 AU — comparable to the inner Solar System. Its orbit is highly elliptical (eccentricity 0.32), swinging dramatically closer to and farther from its star.
How Was GJ 3138 d Discovered?
GJ 3138 d was discovered in 2017 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 GJ 3138 d?
GJ 3138 d is 92.9 light-years (28.5 parsecs) from Earth. Light arriving here tonight left the planet around the year 1934. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,635,040 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 3138 d scores 0.31, ranking #1,165 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: GJ 3138
GJ 3138
- Spectral type
- M0
- Surface temperature
- 3,717 K (Sun: 5,772 K)
- Mass
- 0.68 M☉
- Radius
- 0.50 R☉
- Luminosity
- 0.0450 L☉
The GJ 3138 Planetary System
GJ 3138 d is one of 3 known planets in the GJ 3138 system. Its siblings:
GJ 3138 d — Complete Data
| Mass (best estimate) | 10.50 Earth masses |
|---|---|
| Orbital period | 257.80 days |
| Orbital distance | 0.698 AU |
| Eccentricity | 0.320 |
| Stellar irradiation | 0.10× Earth |
| Earth Similarity Index | 0.31 |
| Distance from Earth | 92.9 light-years (28.5 parsecs) |
| Constellation | Cetus |
| Discovery method | Radial Velocity |
| Discovery facility | La Silla Observatory |
| Discovery year | 2017 |
Data: NASA Exoplanet Archive, last updated 2017-03-29. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 3138 d
Is GJ 3138 d habitable?
No — GJ 3138 d orbits outside the habitable zone of GJ 3138 and is likely too cold for liquid water on its surface.
How far away is GJ 3138 d?
GJ 3138 d is about 93 light-years from Earth in the constellation Cetus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,635,040 years to get there.
How long is a year on GJ 3138 d?
One orbit around GJ 3138 takes 257.8 Earth days.
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