GJ 3998 c
GJ 3998 c is a super-Earth orbiting GJ 3998 in the constellation Ophiuchus. It lies about 59 light-years from Earth and was discovered in 2016 using the radial velocity method.
Is GJ 3998 c in the Habitable Zone?
GJ 3998 c orbits inside the inner edge of the habitable zone of GJ 3998. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of GJ 3998: 0.171–0.438 AU (conservative: 0.216–0.415 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on GJ 3998 c
GJ 3998 c receives 5.40 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on GJ 3998 c — one full orbit around GJ 3998 — lasts 13.7 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.090 AU — closer to its star than Mercury is to the Sun.
How Was GJ 3998 c Discovered?
GJ 3998 c was discovered in 2016 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 3998 c?
GJ 3998 c is 59.2 light-years (18.1 parsecs) from Earth. Light arriving here tonight left the planet around the year 1967. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,041,920 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 3998 c scores 0.44, ranking #354 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: GJ 3998
GJ 3998
- Surface temperature
- 3,726 K (Sun: 5,772 K)
- Mass
- 0.52 M☉
- Radius
- 0.50 R☉
- Luminosity
- 0.0439 L☉
- Age
- 8.4 billion years (Sun: 4.6)
The GJ 3998 Planetary System
GJ 3998 c is one of 3 known planets in the GJ 3998 system. Its siblings:
GJ 3998 c — Complete Data
| Mass (best estimate) | 6.82 Earth masses |
|---|---|
| Orbital period | 13.73 days |
| Orbital distance | 0.090 AU |
| Stellar irradiation | 5.40× Earth |
| Earth Similarity Index | 0.44 |
| Distance from Earth | 59.2 light-years (18.1 parsecs) |
| Constellation | Ophiuchus |
| Discovery method | Radial Velocity |
| Discovery facility | Roque de los Muchachos Observatory |
| Discovery year | 2016 |
Data: NASA Exoplanet Archive, last updated 2025-03-11. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 3998 c
Is GJ 3998 c habitable?
No — GJ 3998 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is GJ 3998 c?
GJ 3998 c is about 59 light-years from Earth in the constellation Ophiuchus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,041,920 years to get there.
How long is a year on GJ 3998 c?
One orbit around GJ 3998 takes 13.7 Earth days — short enough that 27 of its years would fit into one Earth year.
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