Host star — GJ 3378
- Spectral type
- M4 V
- Temperature
- 3,340 K
- Radius
- 0.28 R☉
- Mass
- 0.26 M☉
- Luminosity
- 0.009 L☉
- Distance
- 7.7 pc (25.2 ly)
Red dwarf — the most common type of star. Cool and small.
Very cool — a faint red dwarf.
GJ 3378 b
Orbits GJ 3378 · 25.2 light-years from Earth
RockyRadial Velocity2026ESI 87 · Very Earth-like
Radius
1.32×
Earth
Mass
2.3×
Earth
Year
21d
Temp
272 K
-1°C
Gravity
1.3×
Earth
Distance
25.2
ly
Could life exist here?
AI analysisGJ 3378 b is a rocky world just 32 percent larger than Earth with a mass of 2.3 Earth masses, orbiting an M-dwarf star only 25.2 light-years away. Its equilibrium temperature of 272 Kelvin places it near Earth's mean surface temperature, making it one of the more temperate exoplanets known, and its circular orbit ensures stable, predictable conditions for any potential biosphere. The planet completes each orbit in just 21.4 days around a cool, dim star roughly one-quarter the mass and radius of our Sun. However, such close proximity to its host star raises the possibility of tidal locking, which would create a scorched dayside and a frozen night side—a configuration hostile to life as we understand it, though perhaps not entirely insurmountable if atmospheric circulation could redistribute heat. The planet's density of 5.5 grams per cubic centimeter suggests an Earth-like rocky composition with a substantial iron core. Its habitability score of 87 out of 100 reflects genuine promise, yet confirmation of its atmospheric composition and precise rotational state remains crucial before declaring it a genuine refuge for extraterrestrial life. GJ 3378 b's recent discovery via radial velocity in 2026 makes it a compelling target for upcoming atmospheric characterization with next-generation space telescopes.
What it would be like
GJ 3378 b is a rocky world, potentially similar in composition to Earth or Mars — a solid surface you could, in theory, stand on.
Surface gravity is about 1.3g — noticeably heavier what you're used to on Earth.
With an equilibrium temperature around -1°C, this planet sits in the temperature range where liquid water could potentially exist on the surface — a key ingredient for life as we know it.
An orbital period of 21 days makes the year 17.0× shorter than Earth's. You'd celebrate your birthday more often here.
Earth comparison
Logarithmic bars so Jupiter-class planets fit the same scale as Earth-size worlds.
Radius1.32R⊕
1/25×Earth = 125×
Mass2.30M⊕
1/10000×Earth = 110000×
Surface gravity1.32g
1/100×Earth = 1100×
Equilibrium temp272 K(-1°C)
0 KEarth 255 K2500 K
Side-by-side with Earth
Temperature in context
Liquid N₂Mars avgEarth eq.Earth sfc.Boiling H₂OVenus
Discovery & orbit
- Method
- Radial Velocity
- Year
- 2026
- Facility
- Mauna Kea Observatory
- Semi-major axis
- 0.0967 AU
- Period
- 21.45 days
- Eccentricity
- 0.0000
- Density
- 5.50 g/cm³
Detected by the star's wobble — gravitational tug from the orbiting planet shifts spectral lines.
Nearly circular orbit.
Rocky composition likely. Earth is 5.51 g/cm³.
Discovered via · Radial velocity
The star's wobble — gravitational tug from the planet shifts its spectrum
A planet orbiting a star pulls it slightly back and forth. That motion compresses the star's light when moving toward us (blueshift) and stretches it away (redshift). Precision spectrographs detect the wobble at metres-per-second — enough to infer a planet's mass and orbit.
- Overall share
- ~19% of discoveries
- Best for
- Massive, close-in planets around nearby bright stars
Orbital Animation
GJ 3378GJ 3378 bOrbitHabitable zone
Drag to rotate · scroll to zoomSemi-major axis: 0.097 AUEccentricity: 0.0000Period: 21.4 days
Hertzsprung–Russell Diagram
Where this host star sits among … exoplanet host stars. The main sequence band runs diagonally — giants and supergiants sit above, white dwarfs below.
OBAFGKMCurrent star
How far is 25.2 light-years?
- A light beam leaving Earth right now would arrive in 25.2 years.
- At Voyager 1's speed (17 km/s), the trip would take approximately 444,202 years.
- A radio signal sent today would arrive in 25.2 years — and the reply wouldn't come back for twice that.
Earth Similarity Index
87/1000 — Nothing like Earth100 — Identical to Earth
ESI combines radius similarity and equilibrium temperature similarity. Earth = 100. Mars ≈ 73. Venus ≈ 44. This score reflects two physical parameters only — not atmosphere, water, or magnetic field.