Mini-Neptune · GJ 3998

GJ 3998 c

ExoplanetsDiscovered 2016

Scientific overview

GJ 3998 c is a mini-neptune orbiting GJ 3998, completing an orbit every 14 days, about 59 light-years from Earth. It was discovered in 2016 using the radial velocity method.

Host star

GJ 3998

Spectral type

Temperature

3,726 K

Mass

0.52 M☉

Planetary system — GJ 3998 system

View the GJ 3998 system (3 known planets).

Planet	Class	Radius (R⊕)	Period (d)	Distance (ly)
GJ 3998 bRadial Velocity · 2016	Terrestrial planet	1.39	2.6503	59
GJ 3998 cRadial Velocity · 2016	Mini-Neptune	2.5	13.727	59
GJ 3998 dRadial Velocity · 2025	Super-Earth	2.34	41.78	59

Discovery and detection

Detection method

Radial Velocity Method

Discovery year

2016

Discovered at

Roque de los Muchachos Observatory

Knowledge connections

OrbitsGJ 3998
Member of systemGJ 3998 system
Discovered by methodRadial Velocity Method
Discovered atRoque de los Muchachos Observatory
Catalogued inNASA Exoplanet Archive

Quick facts

Class: Mini-Neptune
Host star: GJ 3998
Discovery method: Radial Velocity Method
Discovery year: 2016
Orbital period: 13.727 d
Semi-major axis: 0.09 AU
Eccentricity: 0
Radius: 2.5 R⊕
Mass: 6.82 M⊕
Density: 2.41 g/cm³ · derived
Equilibrium temp.: 423 K
Insolation: 5.4 S⊕
Distance: 59 ly

Density is derived from the archive mass and radius via ρ = M / (4⁄3·π·r³); all other values are catalogued measurements.

Derived values

Computed from source-backed inputs via standard formulae — not observations. Every input and constant is traced below.

Bulk density2.41 g/cm³derived
Formula & inputs
Formula: ρ = M / (4⁄3·π·r³) (v1.0.0, impl v1.0.0)
Inputs:
- massEarth = 6.82 M⊕ · NASA
- radiusEarth = 2.5 R⊕ · NASA
Assumptions: M⊕ = 5.972e+24 kg, R⊕ = 6371000 m (IAU 2015 B3 nominal); Assumes a uniform sphere.
Limitations: Withheld above 30 g/cm³ (inconsistent mass/radius inputs).; Archive mass/radius carry no propagated uncertainty here.
Uncertainty: not propagated (inputs carry no catalogued uncertainty)
Computed as of 2026-06-29.

Quality & authority

Partial

Unreviewed

Description: Complete
Source coverage: Partial
Relationship coverage: Complete
Review coverage: None
Citation coverage: None
Image coverage: Not applicable

Data from the NASA Exoplanet Archive. See source quality.