TRAPPIST-1
What is TRAPPIST-1?
Stars· Distance 40 ly · size 0.12× Sun (Jupiter-sized). A tiny red dwarf 40 light-years away in Aquarius that made headlines in 2017 when seven Earth-sized planets were found circling it at once. Three or four sit in the zone where liquid water could exist, making it a prime target for the James Webb telescope.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where TRAPPIST-1 is in your sky right now: https://nowsky.org/solar/sky?sel=trappist-1 — location and time set automatically, no login.
Stellar figures
| Distance | 40.7 ly |
|---|---|
| Planets | 7, all Earth-sized |
| Size | an ultracool dwarf barely larger than Jupiter |
| Constellation | Aquarius |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- How far is TRAPPIST-1 from Earth?
- 40.7 ly.
- In one line, what is TRAPPIST-1?
- Stars — A tiny red dwarf 40 light-years away in Aquarius that made headlines in 2017 when seven Earth-sized planets were found circling it at once.
- What can I see of TRAPPIST-1 here?
- You can see the figures and story on this page.
- Where is TRAPPIST-1 in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
How a telescope's name became a star's
TRAPPIST-1 takes its name from TRAPPIST, a 60 cm robotic telescope built in Chile by the University of Liège in Belgium. The letters stand for "TRAnsiting Planets and PlanetesImals Small Telescope", but the name is a pun on the beer of Belgium's Trappist monasteries. This telescope found the first three transiting planets in 2015, and the Spitzer Space Telescope then confirmed four more to make seven.
A small telescope made a large discovery because the target was well chosen. The star is only Jupiter-sized, so an Earth-sized planet crossing it dims the light by a full percent, detectable at 60 cm — Earth crossing the Sun dims it by 0.01 percent. The seven planets are lettered b to h, and because the star's surface is a cool 2,600 K, e, f and g fall within the range for liquid water. Webb has been testing them one by one for atmospheres since 2023, and the inner b and c appear to have none or almost none.
The star in depth
TRAPPIST-1 is an ultracool red dwarf with just 9% of the Sun's mass. It is barely larger than Jupiter and its surface is only about 2,600 K, so despite lying a mere 40 light-years away it is a feeble 19th-magnitude speck. The name comes from TRAPPIST, the small Chilean telescope that first caught its planets.
The February 2017 announcement of seven Earth-sized planets around it was one of the landmark moments in exoplanet science. All seven orbit far inside where Mercury would be, with periods from 1.5 to 19 days, locked in a chain of orbital resonances. Because the star is so cool, three of them — e, f and g — fall within the habitable zone even at that closeness. The James Webb Space Telescope is now testing each for an atmosphere.
No amateur telescope will show the star, but selecting TRAPPIST-1 in the Sky view reveals which direction in Aquarius this little system lies. Travel that way at light speed for forty years and seven Earth-like worlds await.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.