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Entering orbit…
Habitability
10/ 100
Uninhabitable
TRAPPIST-1 h rendered in TerraForge from its measured mass, orbit and star

TRAPPIST-1 h

Also written TRAPPIST-1h, TRAPPIST 1h, TRAPPIST 1 h

Ice World40 light years awayFound 2017
Mass
0.33 × Earth
Radius
0.76 × Earth
Gravity
0.57 g
Surface (est.)
174 K
Year
18.8 days
From Earth
40.4 ly
Mass
0.33 × Earth
Radius
0.76 × Earth
Gravity
0.57 g
Surface (est.)
174 K
Year
18.8 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 AU0.4 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 AUYou are here0.3 M⊕
Habitable zone

Star and planets drawn to scale: the star is 17 times as wide as TRAPPIST-1 h, so only its edge is in view. Orbits spaced as in the star system view.

TRAPPIST-1 h is the outermost and smallest of the seven planets around TRAPPIST-1, a small, cool red dwarf about 40 light-years away. It is about three-quarters of Earth's width and about a third of its mass. Its orbit, every 18.77 days, was the last piece of the system's puzzle.

Surface. Frozen surface covered in water ice, possible subsurface ocean if tidal heating present

Ice World
Life unlikely — too cold for liquid waterLow Activity
TRAPPIST-1 h orbits at 0.06 AU from its star, resulting in frigid temperatures of 174K.
Ice worlds form beyond the frost line where temperatures are low enough for water and other volatiles to freeze solid. They may have subsurface oceans beneath thick ice shells.
Classification Criteria:
✓ Distance: 0.06 AU (>3 AU) or Temperature <200K✓ Temperature: 174K✓ Water content: 35.7% for ice formation

Reading TRAPPIST-1 h’s atmosphere

Dominant elements: O, Si, Fe, N, H, CThis is what a telescope would measure while TRAPPIST-1 h 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 h 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.Imagined LifeJames Trefil & Michael SummersWhat could live on a world like this one: ice shells, supergravity, tidally locked twilight.Envisioning ExoplanetsMichael CarrollWhat these worlds might look like from the ground, painted from the same measurements this page renders.
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Habitability ScoreUninhabitable
10
Contributing Factors
temperature17
Very cold - water frozen, challenging for life
atmosphere42

Thin nitrogen and methane atmosphere

Nitrogen atmosphere provides protection but not breathable (partially stripped by slow rotation)
water11
Limited water content - frozen solid, no liquid phase at this temperature
magnetic Field30
No magnetic field - vulnerable to solar radiation
geology60
Some geological activity provides slow nutrient cycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation30
Very slow rotation - days and nights each last several Earth days, bringing severe temperature swings

Physical Properties

Mass
0.33x Earth (1.95e+24 kg)
Radius
0.69x Earth (4,385 km)
This planet: 0.69× Earth radiusEarth: 1× (baseline)
Surface Gravity
0.69x Earth (6.8 m/s²)
Surface Temperature
174 K (-99 °C / -147 °F)
Rotation Period
451.2 hours/day (slower than Earth)
This planet: 451 h/dayEarth: 24 h/day

Elemental Composition

How TerraForge built this world

TRAPPIST-1 h, from the NASA Exoplanet Archive (found 2017). Measured: 0.326 Earth masses, 0.0619 AU, a 2566 K M-type star. Composition inferred from a measured bulk density of 0.76x Earth's at this size, suggesting roughly 5% water/ice by mass, with a day locked to its 18.8-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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