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Entering orbit…
Habitability
48/ 100
Marginal
Gliese 12 b rendered in TerraForge from its measured mass, orbit and star

Gliese 12 b

Also written Gliese 12b

Rocky Terrestrial40 light years awayFound 2024
Mass
0.95 × Earth
Radius
0.93 × Earth
Gravity
1.10 g
Surface (est.)
318 K
Year
12.8 days
From Earth
39.8 ly
Mass
0.95 × Earth
Radius
0.93 × Earth
Gravity
1.10 g
Surface (est.)
318 K
Year
12.8 days
From Earth
39.8 ly

Gliese 12 system

Type
M-type (Red Dwarf)
Spectral type
M4 V
Temperature
3,328 K
Radius
0.265 ☉
Mass
0.255 ☉
Planets
1
Luminosity
7.28e-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.

Gliese 12 b0.067 AUYou are here0.9 M⊕
Habitable zone

Star and planets drawn to scale: the star is 31 times as wide as Gliese 12 b, so only its edge is in view. Orbits spaced as in the star system view.

Gliese 12 b is the nearest known temperate, Earth-sized planet that crosses in front of its star, and it is often described as an exo-Venus. It orbits Gliese 12, a small, quiet red dwarf about 40 light-years away, every 12.76 days, and is about 0.93 to 1 times Earth's width.

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 possibleModerate Activity
Gliese 12 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: 0.9x Earth (terrestrial range)

Reading Gliese 12 b’s atmosphere

Dominant elements: O, Si, Fe, N, C, HThis is what a telescope would measure while Gliese 12 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.Gliese 12 b sits about 40 light-years away, found by the transit 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
48
Contributing Factors
temperature84
Warm - livable, but heat stress grows with every degree
atmosphere42

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
rotation30
Very slow rotation - days and nights each last several Earth days, bringing extreme temperature swings

Physical Properties

Mass
0.95x Earth (5.67e+24 kg)
Radius
0.98x Earth (6,263 km)
This planet: 0.98× Earth radiusEarth: 1× (baseline)
Surface Gravity
0.98x Earth (9.6 m/s²)
Surface Temperature
318 K (45 °C / 113 °F)
Rotation Period
307.2 hours/day (slower than Earth)
This planet: 307 h/dayEarth: 24 h/day

Elemental Composition

How TerraForge built this world

Gliese 12 b, from the NASA Exoplanet Archive (found 2024). Measured: 0.95 Earth masses, 0.067 AU, a 3328 K M-type star. Composition inferred from a measured bulk density of 1.18x Earth's, which is rock and iron, with a day locked to its 12.8-day year, as anything orbiting this close would be.

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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