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Entering orbit…
Habitability
30/ 100
Extremely Harsh
Proxima Cen d rendered in TerraForge from its measured mass, orbit and star

Proxima Cen d

Also written Proxima Cend

Rocky Terrestrial4 light years awayFound 2025
Mass
0.26 × Earth
Radius
0.69 × Earth
Gravity
0.54 g
Surface (est.)
325 K
Year
5.1 days
From Earth
4.2 ly
Mass
0.26 × Earth
Radius
0.69 × Earth
Gravity
0.54 g
Surface (est.)
325 K
Year
5.1 days
From Earth
4.2 ly

Proxima Cen system

Type
M-type (Red Dwarf)
Spectral type
M5.5 V
Temperature
2,900 K
Radius
0.141 ☉
Mass
0.122 ☉
Planets
2
Luminosity
1.51e-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.

Proxima Cen d0.029 AUYou are here0.3 M⊕
Proxima Cen b0.049 AU1.1 M⊕
Habitable zone

Star and planets drawn to scale: the star is 22 times as wide as Proxima Cen d, 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

Proxima d is one of the lightest planets ever found by watching a star wobble. It orbits Proxima Centauri, the closest star to the Sun at about 4.2 light-years, and its minimum mass is about a quarter of Earth's, roughly twice the mass of Mars. A team led by João Faria announced it in 2022 from a large set of measurements with ESPRESSO, a spectrograph on the European Southern Observatory's Very Large Telescope in Chile.

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 possibleNone Activity
Proxima Cen d 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: 0.3x Earth (terrestrial range)

Reading Proxima Cen d’s atmosphere

Dominant elements: O, Si, Fe, N, C, HThis is what a telescope would measure while Proxima Cen d 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.Proxima Cen d sits about 4 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.
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Habitability ScoreExtremely Harsh
30
Contributing Factors
temperature69
Warm - livable, but heat stress grows with every degree
atmosphere70

Thin CO₂ and nitrogen atmosphere

Nitrogen atmosphere provides protection but not breathable
water26
Limited water content (low gravity lets water escape to space)
magnetic Field30
No magnetic field - vulnerable to solar radiation
geology30
Geologically dead - no nutrient recycling
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
0.26x Earth (1.55e+24 kg)
Radius
0.64x Earth (4,066 km)
This planet: 0.64× Earth radiusEarth: 1× (baseline)
Surface Gravity
0.64x Earth (6.3 m/s²)
Surface Temperature
325 K (52 °C / 126 °F)
Rotation Period
122.9 hours/day (slower than Earth)
This planet: 123 h/dayEarth: 24 h/day

Elemental Composition

How TerraForge built this world

Proxima Cen d, from the NASA Exoplanet Archive (found 2025). Measured: 0.26 Earth masses, 0.0288 AU, a 2900 K M-type star. Composition inferred from an estimated bulk density of 0.78x 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 5.1-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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