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Entering orbit…
Habitability
10/ 100
Uninhabitable

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.

TRAPPIST-1 h

Ice WorldUninhabitable40 light years awayFound 2017

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.

Host star

TRAPPIST-1

Type
M-type (Red Dwarf)
Spectral type
M8.0 V
Temperature
2,566 K
Radius
0.119 ☉
Mass
0.0898 ☉
Known planets
7, including this one
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.

Ice World

No life — too cold for liquid waterNone Activity
Why is this a Ice World?Your planet 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
Further reading
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.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 ScoreUninhabitable
10
Contributing Factors
temperature20
Very cold - water frozen, challenging for life
atmosphere42
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
geology30
Geologically dead - no nutrient recycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation30
Very slow rotation - severe temperature swings between eternal day and night sides

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

Orbital Environment

Star Type
M-type (Red Dwarf)
Distance from Star
0.06 AU (9.26 million km)
Orbital Period
10 days

Atmosphere

Thin nitrogen and methane atmosphere

Elemental Composition

O - Oxygen
31.1%
Si - Silicon
23.8%
Fe - Iron
12.0%

Surface Characteristics

Frozen surface covered in water ice, possible subsurface ocean if tidal heating present
A binary star system's orrery: two suns close together, a red dashed dead-zone boundary, and a debris trail left by a destroyed world

New: Binary Star Systems 🌀

A system can now orbit two suns. Add a companion star when you build one — close, medium, or wide — and the physics decides what survives: a shared center of mass carves out a dead zone where gravity from both stars tears a world apart, leaving it as debris, and every surviving planet's orbit goes elliptical, moving fastest at closest approach and slowest out at aphelion. Push the separation to wide and the dead zone opens tens of AU across, wide enough to gut a system that would have been stable around one star alone. Stand on a world that made it through and you'll watch two suns cross the sky together.

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