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
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.