TRAPPIST-1 System
The most planet-rich system known in terms of potentially habitable worlds — seven Earth-sized planets, three in the habitable zone.
Key Facts
- Distance: 39.46 ly from Sol
- Star type: M8V ultra-cool red dwarf
- Star mass: 0.089 solar masses (barely above brown dwarf threshold)
- Star luminosity: 0.000524 solar
- Discovered: 2016 (3 planets), 2017 (full 7-planet system by NASA Spitzer)
- Age: 7.6 billion years (older than our solar system)
The Seven Worlds
All seven planets are closer to their star than Mercury is to the Sun. The entire system would fit inside Mercury’s orbit.
| Planet | Radius (Earth) | Mass (Earth) | Orbit (days) | Equilibrium Temp | HZ? |
|---|---|---|---|---|---|
| b | 1.12 | 1.37 | 1.51 | 400 K | Too hot |
| c | 1.10 | 1.38 | 2.42 | 342 K | Inner edge |
| d | 0.79 | 0.41 | 4.05 | 288 K | Yes |
| e | 0.92 | 0.69 | 6.10 | 251 K | Yes (best candidate) |
| f | 1.04 | 1.04 | 9.21 | 219 K | Yes |
| g | 1.13 | 1.32 | 12.35 | 199 K | Outer edge |
| h | 0.77 | 0.33 | 18.77 | 173 K | Too cold |
TRAPPIST-1e is the most Earth-like: similar size, mass, density, and receives similar stellar flux to Earth. It’s the prime target for atmospheric characterization.
JWST Observations
JWST has been observing TRAPPIST-1 planets since 2022:
- TRAPPIST-1b: Likely no thick atmosphere (2023 thermal emission data)
- TRAPPIST-1c: Likely no thick CO2 atmosphere (2023)
- TRAPPIST-1e, f, g: Still being characterized — these are the high-priority targets
The results so far are sobering: the inner planets appear atmosphere-stripped, likely by stellar activity. The habitable-zone planets (d, e, f) remain the best hope.
Travel Considerations
At 39.46 ly, TRAPPIST-1 is ~10x farther than dest-alpha-centauri:
| Speed | Travel Time |
|---|---|
| 0.1c | ~395 years |
| 0.2c | ~197 years |
| 0.5c | ~79 years |
| 0.9c | ~44 years (ship time ~19 years via concept-time-dilation) |
This is firmly in tech-generation-ship or tech-cryosleep territory unless near-relativistic speeds are achieved. Not a first-generation interstellar target, but a compelling second-generation one if habitable atmospheres are confirmed.
Why It Matters
TRAPPIST-1 is the best-known laboratory for comparative planetology — seven rocky worlds around the same star, spanning a range of conditions. If any system beyond our own harbors detectable biosignatures, this is the leading candidate.