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Entering orbit…
Habitability
43/ 100
Marginal
TRAPPIST-1 d rendered in TerraForge from its measured mass, orbit and star

TRAPPIST-1 d

Also written TRAPPIST-1d, TRAPPIST 1d, TRAPPIST 1 d

Rocky Terrestrial40 light years awayFound 2016
Mass
0.39 × Earth
Radius
0.79 × Earth
Gravity
0.62 g
Surface (est.)
289 K
Year
4.0 days
From Earth
40.4 ly
Mass
0.39 × Earth
Radius
0.79 × Earth
Gravity
0.62 g
Surface (est.)
289 K
Year
4.0 days
From Earth
40.4 ly

TRAPPIST-1 system

Type
M-type (Red Dwarf)
Spectral type
M8.0 V
Temperature
2,566 K
Radius
0.119 ☉
Mass
0.0898 ☉
Planets
7
Luminosity
5.53e-4 ☉

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.

TRAPPIST-1 b0.011 AU1.4 M⊕
TRAPPIST-1 c0.016 AU1.3 M⊕
TRAPPIST-1 d0.022 AUYou are here0.4 M⊕
TRAPPIST-1 e0.029 AU0.7 M⊕
TRAPPIST-1 f0.038 AU1.0 M⊕
TRAPPIST-1 g0.047 AU1.3 M⊕
TRAPPIST-1 h0.062 AU0.3 M⊕
Habitable zone

Star and planets drawn to scale: the star is 16 times as wide as TRAPPIST-1 d, so only its edge is in view. Orbits spaced as in the star system view.

TRAPPIST-1 d sits roughly where you would hope to find a second Earth, and the James Webb Space Telescope has now looked closely enough to say it is not one. The planet is a little smaller than Earth, about 0.79 times its width and 0.39 times its mass. It orbits only about 2 percent of Earth's distance from the Sun, so its year lasts about four days. Its red dwarf star is so dim that this tight orbit gives d about the same amount of energy that Earth receives from the Sun.

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 possibleLow Activity
TRAPPIST-1 d is dominated by silicate (24.2%) and iron (12.1%) 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: 24.2% + Iron: 12.1% + Magnesium: 3.6%✓ Mass: 0.4x Earth (terrestrial range)

Reading TRAPPIST-1 d’s atmosphere

Dominant elements: O, Si, Fe, N, H, CThis is what a telescope would measure while TRAPPIST-1 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.TRAPPIST-1 d 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
43
Contributing Factors
temperature100
Optimal temperature range for liquid water and life
atmosphere70

Thin CO₂ and nitrogen atmosphere

Nitrogen atmosphere provides protection but not breathable
water33
Limited water content (low gravity lets water escape to space)
magnetic Field30
No magnetic field - vulnerable to solar radiation
geology60
Some geological activity provides slow nutrient cycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation65
Slow rotation - significant day/night temperature variations, but life can adapt

Physical Properties

Mass
0.39x Earth (2.32e+24 kg)
Radius
0.73x Earth (4,647 km)
This planet: 0.73× Earth radiusEarth: 1× (baseline)
Surface Gravity
0.73x Earth (7.2 m/s²)
Surface Temperature
289 K (16 °C / 61 °F)
Rotation Period
97.2 hours/day (slower than Earth)
This planet: 97 h/dayEarth: 24 h/day

Time Dilation

Clocks run 6.3 seconds per year slower than deep space — about 8 minutes over a lifetime

Elemental Composition

How TerraForge built this world

TRAPPIST-1 d, from the NASA Exoplanet Archive (found 2016). Measured: 0.388 Earth masses, 0.0223 AU, a 2566 K M-type star. Composition inferred from a measured bulk density of 0.79x Earth's, which is rock and iron, with a day locked to its 4.0-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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