Host star — TRAPPIST-1
- Spectral type
- M8.0 V
- Temperature
- 2,566 K
- Radius
- 0.12 R☉
- Mass
- 0.09 M☉
- Luminosity
- 0.001 L☉
- Distance
- 12.4 pc (40.5 ly)
Red dwarf — the most common type of star. Cool and small.
Very cool — a faint red dwarf.
TRAPPIST-1 d
Orbits TRAPPIST-1 · 40.5 light-years from Earth
RockyTransit2016ESI 82 · Very Earth-like
Radius
0.79×
Earth
Mass
0.4×
Earth
Year
4d
Temp
286 K
13°C
Gravity
0.6×
Earth
Distance
40.5
ly
Could life exist here?
AI analysisTRAPPIST-1 d is a rocky world roughly four-fifths Earth's radius with an equilibrium temperature of 286 Kelvin—cool enough that liquid water could persist on its surface, assuming a protective atmosphere. Its 4.05-day orbit around an exceptionally dim red dwarf star (only 0.119 times the Sun's radius) places it much closer to its host than Mercury is to our Sun, yet the star's feeble output keeps the planet temperate rather than scorched. The planet's density of 4.37 grams per cubic centimeter suggests an iron-rich composition similar to Earth's, a promising sign for geology and magnetism. However, significant uncertainties remain: we don't know whether TRAPPIST-1 d has retained an atmosphere, what its surface composition actually is, or whether tidal forces from such a close orbit have stripped away volatiles or locked the planet's rotation. Its habitability score of 82 out of 100 reflects genuine potential, not certainty. TRAPPIST-1 d's membership in a compact seven-planet system just 40.5 light-years away makes it one of the nearest candidates for biosignature searches by future telescopes.
What it would be like
TRAPPIST-1 d is a rocky world, potentially similar in composition to Earth or Mars — a solid surface you could, in theory, stand on.
Surface gravity is about 0.6g — noticeably lighter what you're used to on Earth.
With an equilibrium temperature around 13°C, this planet sits in the temperature range where liquid water could potentially exist on the surface — a key ingredient for life as we know it.
A year here is only 4.0 Earth days. Seasons, if they exist, change in a matter of hours.
Earth comparison
Logarithmic bars so Jupiter-class planets fit the same scale as Earth-size worlds.
Radius0.79R⊕
1/25×Earth = 125×
Mass0.39M⊕
1/10000×Earth = 110000×
Surface gravity0.62g
1/100×Earth = 1100×
Equilibrium temp286 K(13°C)
0 KEarth 255 K2500 K
Side-by-side with Earth
Temperature in context
Liquid N₂Mars avgEarth eq.Earth sfc.Boiling H₂OVenus
Discovery & orbit
- Method
- Transit
- Year
- 2016
- Facility
- La Silla Observatory
- Semi-major axis
- 0.0223 AU
- Period
- 4.05 days
- Eccentricity
- 0.0084
- Density
- 4.37 g/cm³
Detected by measuring the tiny dip in starlight as the planet crosses in front of its star.
Nearly circular orbit.
Rocky composition likely. Earth is 5.51 g/cm³.
Discovered via · Transit
Tiny dip in starlight as the planet crosses in front of its star
A transit photometer watches a star nonstop and measures its brightness to ~0.01%. When a planet passes between us and the star, the star dims briefly — the deeper the dip, the bigger the planet. This is how Kepler and TESS found most known exoplanets.
- Overall share
- ~75% of all confirmed worlds
- Best for
- Earth-to-Neptune-sized planets on short orbits
Orbital Animation
TRAPPIST-1TRAPPIST-1 dOrbitHabitable zone
Drag to rotate · scroll to zoomSemi-major axis: 0.022 AUEccentricity: 0.0084Period: 4.0 days
Hertzsprung–Russell Diagram
Where this host star sits among … exoplanet host stars. The main sequence band runs diagonally — giants and supergiants sit above, white dwarfs below.
OBAFGKMCurrent star
How far is 40.5 light-years?
- A light beam leaving Earth right now would arrive in 40.5 years.
- At Voyager 1's speed (17 km/s), the trip would take approximately 714,952 years.
- A radio signal sent today would arrive in 40.5 years — and the reply wouldn't come back for twice that.
Earth Similarity Index
82/1000 — Nothing like Earth100 — Identical to Earth
ESI combines radius similarity and equilibrium temperature similarity. Earth = 100. Mars ≈ 73. Venus ≈ 44. This score reflects two physical parameters only — not atmosphere, water, or magnetic field.