Confirmed exoplanet · Database record + computed analysis
GJ 3138 d
A confirmed world orbiting GJ 3138, 92.9 light-years away.
A sub-Neptune
3.23 Earth radii, likely a rocky core under a thick gas or steam envelope rather than a walkable surface. At only 10.5 Earth masses for that size, it must be substantially gas or volatile ices: puffy, not rocky.
The orbit
Its year takes 258 Earth days (0.7 Earth years). The orbit is strongly stretched (eccentricity 0.32), so its distance from the star, and with it the climate, swings dramatically.
Temperature and starlight
Its equilibrium temperature (the airless-world estimate) is about -121 °C. It receives only 0.10 times Earth's starlight.
Its sun
Its star is a red dwarf (3,717 K surface), type M0: small, dim, flare-prone, and destined to outlive the Sun many times over. It shares the system with 2 other known planets.
How far is that, really?
At 93 light-years, tonight's light from this system left it around the year 1933. A Voyager-speed probe would need roughly 1,642,945 years to get there.
How we found it
It was found by the radial-velocity method: the planet's gravity swings its star in a small circle, and that wobble shows up as a rhythmic Doppler shift in the starlight. The wobble's size gives the planet's minimum mass. The discovery was announced in 2017 from La Silla Observatory.
Everything above is computed from the archive’s measured values for this planet. Where a quantity is missing, the statement is omitted rather than guessed.
About this record
The measured values come from the NASA Exoplanet Archive, and any missing value has not been determined yet; the Atlas never fills gaps with guesses. More standout worlds: Proxima b, TRAPPIST-1e, K2-18 b, 55 Cancri e, and the detection methods that found them all.