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Entering orbit…
Habitability
42/ 100
Marginal
GJ 3378 b rendered in TerraForge from its measured mass, orbit and star

GJ 3378 b

Also written GJ 3378b

Rocky Terrestrial25 light years awayFound 2026
Mass
2.30 × Earth
Radius
1.32 × Earth
Gravity
1.32 g
Surface (est.)
275 K
Year
21.4 days
From Earth
25.2 ly
Mass
2.30 × Earth
Radius
1.32 × Earth
Gravity
1.32 g
Surface (est.)
275 K
Year
21.4 days
From Earth
25.2 ly

GJ 3378 system

Type
M-type (Red Dwarf)
Spectral type
M4 V
Temperature
3,340 K
Radius
0.275 ☉
Mass
0.262 ☉
Planets
1
Luminosity
8.50e-3 ☉

Published by the NASA Exoplanet Archive. This world’s temperature and habitability score are computed from this star’s measured luminosity, not from a stand-in for its class.

GJ 3378 b0.097 AUYou are here2.3 M⊕
Habitable zone

Star and planets drawn to scale: the star is 23 times as wide as GJ 3378 b, so only its edge is in view. Orbits spaced as in the star system view.

Estimated: this planet doesn't transit its star, so its size is inferred, not measured

GJ 3378 b, from the NASA Exoplanet Archive (found 2026). Measured: 2.3 Earth masses, 0.0967 AU, a 3340 K M-type star. Composition inferred from an estimated bulk density of 1.00x Earth's, modeled rather than measured since this isn't a transiting planet — the radius is the archive's estimate, so it can't settle how much water there is; read as rock and iron, with a day locked to its 21.4-day year, as anything orbiting this close would be.

Surface. Rocky surface with impact craters, possible volcanic features

✓ Conditions could support life. This planet’s modelled conditions could support biological processes: stable temperatures, liquid water and the chemistry life as we know it needs. That makes life possible, not present.

Rocky Terrestrial
Life possibleHigh Activity
GJ 3378 b is dominated by silicate (25.0%) and iron (12.5%) content, forming a rocky terrestrial body.
Rocky terrestrial planets are primarily composed of silicate rocks and metals. They're the most common type of small planet in the universe.
Classification Criteria:
✓ Silicon: 25.0% + Iron: 12.5% + Magnesium: 3.8%✓ Mass: 2.3x Earth (terrestrial range)

Reading GJ 3378 b’s atmosphere

Dominant elements: O, Si, Fe, N, C, HThis is what a telescope would measure while GJ 3378 b crosses in front of its star: starlight passes through the atmosphere and spreads into a rainbow band. Each dark line marks a wavelength the atmosphere absorbed.Every element absorbs its own signature wavelengths — hydrogen always darkens the same two spots, calcium another pair, and so on. Astronomers match the lines in a real spectrum against a library of these signatures to say what an atmosphere is made of, light-years away, without ever visiting. A deeper line generally means more of that element is present.GJ 3378 b sits about 25 light-years away, found by the radial velocity method. Most catalogued distances trace back to parallax: as Earth orbits the Sun, a nearby star appears to shift very slightly against the distant background stars, and the size of that shift gives its distance directly.
Further reading
ExoplanetsSara Seager (editor)The field's standard reference: how planets are found, how they form, and what their atmospheres are made of.The Planet FactoryElizabeth TaskerHow planets are made, and why so few of them come out like Earth.The Little Book of ExoplanetsJoshua WinnHow these worlds are found, and what a measurement can honestly tell us.Exoplanets: Diamond Worlds, Super Earths, Pulsar PlanetsMichael Summers & James TrefilThe strange end of the catalogue — carbon worlds, molten rock, planets orbiting dead stars.
As an Amazon Associate I earn from qualifying purchases — if you buy through these links, TerraForge may receive a small commission at no extra cost to you.
Habitability ScoreMarginal
42
Contributing Factors
temperature100
Optimal temperature range for liquid water and life
atmosphere28

Thin CO₂ and nitrogen atmosphere

Nitrogen atmosphere provides protection but not breathable (partially stripped by slow rotation)
water50
Limited water content
magnetic Field30
No magnetic field - vulnerable to solar radiation
geology90
Active geology recycles nutrients and drives carbon cycle
Organic Chemistry80
Core organic elements (CHNO) present
rotation10
Near tidally locked - one hemisphere perpetually scorched, other frozen, narrow habitable twilight zone only

Physical Properties

Mass
2.30x Earth (1.37e+25 kg)
Radius
1.32x Earth (8,410 km)
This planet: 1.32× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.32x Earth (12.9 m/s²)
Surface Temperature
275 K (2 °C / 36 °F)
Rotation Period
513.6 hours/day (slower than Earth)
This planet: 514 h/dayEarth: 24 h/day

Elemental Composition

A dark ringed planet hanging over the horizon of a rocky moon, its rings lit by a distant sun

New: Stand on Your Moons 🌒

A planet's surface view isn't the only ground any more. Press the surface button on a planet with moons and it asks where to stand: the planet itself, or any moon still in orbit, each tagged with what it became — ocean, ice, carbon, volcanic. Every moon gets its own ground and sky from its own physics: airless rock under a black sky, ice cracked by geysers over a hidden sea, sulfur plains shaking with eruptions, or orange haze you can't see the sun through. And hanging over the horizon, there's the planet you built.

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