The GJ 3998 system contains 2 exoplanets. It is located 59.18 light years away from the solar system.
| Mass | 0.5 solar masses |
| Radius | 0.49 solar radiae |
| Temperature | 3722 kelvin |
| Stellar Metallicity | -0.16 decimal exponent |
| Age | - billion years |
At 2.471 Earth masses, GJ 3998 b is a so called Super Earth. Super Earths could be terrestrial worlds like Earth, but they could also be ocean worlds or terrestrial worlds wrapped in a substantial atmosphere, in which case some refer to them as Mini Neptunes.
| Mass | 2.470 Earth masses |
| Density | 5.160 grams per cubic centimeter |
| Radius | 1.380 Earth radiae |
| Semi-major Axis | 0.029 AU |
| Eccentricity | 0 |
| Orbital Period | 2.650 days |
| Discovery Method | Radial Velocity |
| Discovery Facility | Roque de los Muchachos Observatory |
| Discovery Telescope | 3.58 m Telescopio Nazionale Galileo |
| Discovery Instrument | HARPS-N Spectrograph |
| Discovery Date | 2016-10 |
| Reference | Affer et al. 2016 |
At more than 10 Earth masses, GJ 3998 c is an ice giant, a planet that is made up mostly of volatiles like water, amonia and methane, and enveloped by a dense hydrogen and helium atmosphere, much like Uranus and Neptune.
| Mass | 6.260 Earth masses |
| Density | 2.550 grams per cubic centimeter |
| Radius | 2.380 Earth radiae |
| Semi-major Axis | 0.089 AU |
| Eccentricity | 0.049 |
| Orbital Period | 13.740 days |
| Discovery Method | Radial Velocity |
| Discovery Facility | Roque de los Muchachos Observatory |
| Discovery Telescope | 3.58 m Telescopio Nazionale Galileo |
| Discovery Instrument | HARPS-N Spectrograph |
| Discovery Date | 2016-10 |
| Reference | Affer et al. 2016 |