Habitable-zone candidate
TRAPPIST-1
Seven Earth-sized planets around an ultracool dwarf — three in the habitable zone.
- Planets
- 7
- Distance
- 40.5 ly
- Host
- M-type
About TRAPPIST-1
Discovery
Discovered in 2016 by a team led by Michaël Gillon at the University of Liège using the TRAPPIST telescope in Chile, with Spitzer follow-up confirming seven Earth-sized planets in 2017 — the most compact known planetary system around a single star.
Why it matters
Three of TRAPPIST-1's seven planets sit in the habitable zone, and the dim ultracool-dwarf host means transit spectroscopy of each planet's atmosphere is actually feasible. It is the system most likely to give us a first detection of biosignatures on a rocky world.
Current research
JWST thermal phase-curve observations have shown TRAPPIST-1 b and c are consistent with bare rocky surfaces — no thick atmospheres — while observing programs for d, e, f, and g continue to search for atmospheric signatures.
Comparable to
Like a miniature solar system packed inside Mercury's orbit, with all seven planets closer to their star than Mercury is to the Sun.
System geometry
At a glance
- Hostname
- TRAPPIST-1
- Spectral type
- M8.0 V
- Distance
- 40.5 ly · 12.43 pc
- Stellar mass
- 0.09 M☉
- Stellar radius
- 0.12 R☉
- Luminosity
- 5.53e-4 L☉
- Effective temp
- 2566 K
- Confirmed planets
- 7
- Habitable zone
- 0.022 – 0.032 AU
Top-down orbital diagram
Orbits to scale within this system. Dashed green = habitable-zone edges.
Planet positions are illustrative (evenly spaced in phase). For live motion see the 3D scene.
The planets
7 confirmed.
Rocky world
TRAPPIST-1 b
- Orbit
- 0.012 AU
- Period
- 1.51 days
- Radius
- 1.12 R⊕
- Mass
- 1.37 M⊕
- Eq. temperature
- 398 K
- Eccentricity
- 0.006
- Discovered
- 2016 · Transit
Rocky world
TRAPPIST-1 c
- Orbit
- 0.016 AU
- Period
- 2.42 days
- Radius
- 1.10 R⊕
- Mass
- 1.31 M⊕
- Eq. temperature
- 340 K
- Eccentricity
- 0.007
- Discovered
- 2016 · Transit
Rocky world
TRAPPIST-1 d
- Orbit
- 0.022 AU
- Period
- 4.05 days
- Radius
- 0.79 R⊕
- Mass
- 0.39 M⊕
- Eq. temperature
- 286 K
- Eccentricity
- 0.008
- Discovered
- 2016 · Transit
Rocky world
TRAPPIST-1 e
- Orbit
- 0.029 AU
- Period
- 6.10 days
- Radius
- 0.92 R⊕
- Mass
- 0.69 M⊕
- Eq. temperature
- 250 K
- Eccentricity
- 0.005
- Discovered
- 2017 · Transit
Rocky world
TRAPPIST-1 f
- Orbit
- 0.038 AU
- Period
- 9.21 days
- Radius
- 1.04 R⊕
- Mass
- 1.04 M⊕
- Eq. temperature
- 218 K
- Eccentricity
- 0.010
- Discovered
- 2017 · Transit
Ice world
TRAPPIST-1 g
- Orbit
- 0.047 AU
- Period
- 12.35 days
- Radius
- 1.13 R⊕
- Mass
- 1.32 M⊕
- Eq. temperature
- 197 K
- Eccentricity
- 0.002
- Discovered
- 2017 · Transit
Ice world
TRAPPIST-1 h
- Orbit
- 0.062 AU
- Period
- 18.77 days
- Radius
- 0.76 R⊕
- Mass
- 0.33 M⊕
- Eq. temperature
- 172 K
- Eccentricity
- 0.006
- Discovered
- 2017 · Transit
Compared to our Solar System
Each row shows the closest Solar-System analog by radius (log-space). Earth is pinned at the bottom as the constant frame of reference.
| Planet | Radius (R⊕) | Mass (M⊕) | Orbit (AU) | Period (days) | Eq temp (K) | Solar analog |
|---|---|---|---|---|---|---|
| TRAPPIST-1 b | 1.12 | 1.37 | 0.012 | 1.51 | 398 | Earth |
| TRAPPIST-1 c | 1.10 | 1.31 | 0.016 | 2.42 | 340 | Earth |
| TRAPPIST-1 d | 0.79 | 0.39 | 0.022 | 4.05 | 286 | Venus |
| TRAPPIST-1 e | 0.92 | 0.69 | 0.029 | 6.10 | 250 | Venus |
| TRAPPIST-1 f | 1.04 | 1.04 | 0.038 | 9.21 | 218 | Earth |
| TRAPPIST-1 g | 1.13 | 1.32 | 0.047 | 12.35 | 197 | Earth |
| TRAPPIST-1 h | 0.76 | 0.33 | 0.062 | 18.77 | 172 | Venus |
| Earth (reference) | 1.00 | 1.00 | 1.000 | 365.25 | 255 | — |
Research status
◇ JWST observation status
7 planets have confirmed JWST observation time across Cycles 1–3.
- TRAPPIST-1 b
- TRAPPIST-1 c
- TRAPPIST-1 d
- TRAPPIST-1 e
- TRAPPIST-1 f
- TRAPPIST-1 g
- TRAPPIST-1 h
JWST programs include transit spectroscopy, thermal phase curves, and direct imaging coronagraph observations depending on planet class.
Discovery timeline
- 2016
3 planets: b, c, d
via Transit
- 2017
4 planets: e, f, g, h
via Transit
If you liked this
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Kepler-186
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First Earth-sized planet found in another star's habitable zone (2014).
Kepler-442
1 planets · 1193.6 ly · G2V
One of the most "Earth-like" planets ever found by Kepler — 60% bigger, in HZ.
Experience it
See TRAPPIST-1 in interactive 3D
Fly through the system, click any planet, watch orbits play out at 100× speed.
▶ Launch 3D scene