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TRAPPIST-1 d

TRAPPIST-1 · M8.0 V host star · cool red dwarf · main sequence

[ TRAPPIST_1_D.IMG ]
VIEW 1 · ON THE SURFACE
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Artist’s impression of TRAPPIST-1 d: VIEW 1 · ON THE SURFACE
VIEW 1 · ON THE SURFACE · Artist’s impression. No surface has been seen.
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40.5 light-years from Earth
[ FACTS.DAT ]
Right ascension / declination346.626° / -5.043°J2000 / ICRS
Gravity0.62 × Earthderived from measured mass + radius
Year4.05 days
From its star0.0223 AUabout 3.3 million km
Stars in the system1 star7 known planets in system
Stars this world orbits1 starOrbits TRAPPIST-1
Day and nightLikely synchronous spinProbably spins once per orbit, keeping one hemisphere in permanent day and the other in permanent night. Heuristic: likely at ≤0.25 AU, uncertain to 0.50 AU, probably not beyond; rotation is not directly measured.
[ TEMP.EST ]MODELLED, NOT MEASURED
Host star≈2,600 Ktypical M8.0 V · 0.12 Sun radii
No atmosphere266 K · -7°C30% reflective · heat shared
Earth-like air299 K · 26°CBaseline plus 33°C

Star temperature and orbital distance set incoming energy, but stellar size is also required. This calculation uses a typical radius for the listed spectral type, 30% reflectivity and even heat redistribution. It is not a ground-temperature forecast: air, clouds, oceans and surface reflectivity could move the result by tens to hundreds of degrees. A likely synchronous spin also means the permanent day and night sides would not share one ground temperature.

[ STARLIGHT.SPC ]VISIBLE LIGHT ONLY

The marker above the bar is a typical temperature for this star’s class. The line below is Earth’s Sun.

red-orange

TRAPPIST-1 is class M8.0 V. Its visible daylight would be dim and strongly red-orange; most of its energy is infrared.

Representative lit-side geometry only. On a locked world, the star’s real elevation would depend on where you stand.

[ GROUND.TXT ]STILL INFERENCE

Most plausible case. A small, low-density-for-rock world: 0.79 Earth radii and 0.39 Earth masses, so you weigh about 38% less than on Earth, and that pair is measured. The star is an M8 dwarf, 2566 K, only 0.12 solar radii, but from 0.022 AU it spans about 2.9°, more than five times the Sun’s width. The planet receives about Earth’s light. The day side is warm rock or a thin volatile shell, not a deep ice cap. JWST has looked at this system and has not delivered a clear thick atmosphere on the inner planets.

Dry case. Dark rock under a huge red star. Little ice on the day side. The low gravity makes a thin atmosphere easy to lose, so a bare day side is a serious option.

Thick-air case. A steam or high-mean-molecular-weight sky could hide the ground. The measured mass does not leave room for a giant hydrogen envelope.

Walking. About 38% lighter than Earth, measured. TRAPPIST-1 c would look about 1.6 times as wide as the Moon, and planet e about 1.2 times, at closest approach. Those are planets, not moons. The star is magnitude 17, 40 light-years away.

Based on: Agol et al. 2021; Gillon et al. 2017; Teff 2566 K, R 0.119 Rsun, S 1.12, Rp 0.79, Mp 0.39, a 0.022 AU

[ ORBIT.SYS ]7 KNOWN · ALL SHOWN
100% · Above 30°

TRAPPIST-1 d circles TRAPPIST-1. Also shown: TRAPPIST-1 b, TRAPPIST-1 c, TRAPPIST-1 e, TRAPPIST-1 f, TRAPPIST-1 g, TRAPPIST-1 h, each on its NASA-catalogued orbit. Use Higher and Lower to move your viewpoint above, through and below the orbital plane, and − / + to zoom. Orbit shapes and spacing are schematic.

[ SOURCES.TXT ]

Positions, distances, and system parameters come from the NASA Exoplanet Archive composite table, queried 25 Sep 2026. GJ 273 b uses the parallax in that row, 12.4 light-years. The 45 worlds follow Bohl, Lawrence, Lowry, and Kaltenegger.