The TRAPPIST-1 planet most often called potentially habitable

TRAPPIST-1e

Orbits TRAPPIST-1 · 40.5 light-years · discovered 2017 (transit)

TRAPPIST-1e is the fourth of seven planets orbiting TRAPPIST-1, a tiny red dwarf about 40 light-years away. It is slightly smaller than Earth, with about 70% of its mass, and it receives roughly two-thirds of the energy Earth gets from the Sun — squarely within its star's habitable zone.

Climate models have repeatedly singled it out as the TRAPPIST-1 planet most likely to keep liquid water on its surface, if it has a suitable atmosphere. That makes it one of the most closely watched worlds beyond the Solar System, and one of the James Webb Space Telescope's priority targets. Whether it actually has air or water is still unknown.

Key facts

Star: TRAPPIST-1M8V ultracool red dwarf
Distance: 40.5 light-years
Radius: 0.92 × Earth
Mass: 0.69 × Earth
Orbital period: 6.10 days
Equilibrium temperature: 250 K (-23 °C)Before any greenhouse warming
Starlight received: 0.65× Earth's
Surface gravity: ≈ 0.82 gIf rocky
Discovered: 2017Transit

Star: TRAPPIST-1 (M8V ultracool red dwarf)
Distance: About 40.5 light-years
Discovered: 2017, transit
Radius: About 0.92 Earth radii
Mass: About 0.69 Earth masses (from transit timing)
Orbital period: About 6.1 days
Starlight received: About 65% of what Earth gets from the Sun
Equilibrium temperature: About 250 K (−23 °C), assuming it reflects no light and has no atmosphere
Position: Fourth of seven known planets

Measured values follow the NASA Exoplanet Archive and discovery papers; many carry large uncertainties. The 3D globe and walkable surface on this page are an artist's impression generated from these numbers.

What we know

TRAPPIST-1e transits its star, so its radius is well measured, and its mass has been worked out from the way the planets tug on one another's timing. The result is a density a little below Earth's, consistent with a rocky planet that may contain slightly less iron than ours.

It is among the best-characterised small exoplanets in bulk terms. But density alone cannot tell us whether it has oceans, ice or a bare rocky surface.

Its star

TRAPPIST-1 is an ultracool dwarf with roughly 9% of the Sun's mass and a diameter only slightly larger than Jupiter's. Its light is dim and reddish, peaking in the infrared. It flares often and is covered in spots, and it was much brighter in its youth — conditions that may have stripped water and air from its innermost planets.

Could it be habitable?

In many climate simulations, TRAPPIST-1e can sustain surface liquid water across a range of plausible atmospheres, from Earth-like to carbon-dioxide-rich. That robustness is why it is often described as the system's best habitable-zone candidate.

The first JWST transmission results, published in 2025 from four transits, indicated that the planet is unlikely to hold on to a primordial hydrogen-rich atmosphere. They could not rule out a denser secondary atmosphere — for instance one rich in nitrogen — nor a bare surface. The researchers stressed that the results are preliminary and heavily affected by contamination from the star's spots.

Lessons from TRAPPIST-1b and c

JWST thermal measurements in 2023 suggested that the innermost planets, b and c, have little or no thick atmosphere, ruling out, for example, a dense Venus-like carbon dioxide atmosphere on c. Those planets are much hotter than e, so they do not settle its fate, but they show how harsh the environment can be.

Orbit and climate

TRAPPIST-1e orbits about 0.029 astronomical units from its star — around 4.4 million kilometres — and is expected to be tidally locked. If it has an atmosphere, winds would carry heat from the permanent dayside to the night side; without one, the night side would be bitterly cold. Its orbit is in resonance with its neighbours, completing three orbits for every two of TRAPPIST-1f.

Discovery

TRAPPIST-1e was one of four new planets announced in February 2017 by Michaël Gillon's team, using NASA's Spitzer Space Telescope together with ground-based telescopes. The announcement revealed TRAPPIST-1 as the record-holder for the most Earth-sized planets known around a single star.

Future observations

More JWST transits of TRAPPIST-1e are being gathered, with the aim of determining whether it has a secondary atmosphere. Combining many transits, and correcting carefully for the star's activity, is expected to be the only way to detect gases such as carbon dioxide or methane on a planet this small.

About the 3D impression

Artist's impression — the real surface has never been seen. The globe and the surface you can walk on are generated from what is measured — size, the starlight it receives and the kind of star it orbits — using the same procedural engine as our imaginary worlds. Seas, ice, clouds and any plant-like colours are possibilities, not observations: around a red dwarf the daylight is redder, so the scene uses warmer skies and darker vegetation.

Walk on an imagined surface of TRAPPIST-1e

Earth-like exoplanets compared

Well-known potentially Earth-like exoplanets, nearest first
Planet	Distance	Radius	Year	Sunlight
Proxima Centauri b	4.2 ly	—	11.2 days	0.65× Earth
Ross 128 b	11.0 ly	—	9.87 days	1.38× Earth
Teegarden's Star b	12.5 ly	—	4.91 days	1.08× Earth
Gliese 667 Cc	23.6 ly	—	28.1 days	0.88× Earth
TRAPPIST-1d	40.5 ly	0.79 R⊕	4.05 days	1.11× Earth
TRAPPIST-1e	40.5 ly	0.92 R⊕	6.10 days	0.65× Earth
TRAPPIST-1f	40.5 ly	1.04 R⊕	9.21 days	0.37× Earth
TRAPPIST-1g	40.5 ly	1.13 R⊕	12.4 days	0.25× Earth
LHS 1140 b	48.9 ly	1.73 R⊕	24.7 days	0.43× Earth
TOI-700 d	101 ly	1.07 R⊕	37.4 days	0.87× Earth
Kepler-186f	580 ly	1.17 R⊕	129.9 days	0.30× Earth
Kepler-22b	635 ly	2.10 R⊕	289.9 days	1.01× Earth
Kepler-62f	980 ly	1.41 R⊕	267.3 days	0.41× Earth
Kepler-442b	1,194 ly	1.34 R⊕	112.3 days	0.70× Earth
Kepler-452b	1,800 ly	1.63 R⊕	384.8 days	1.10× Earth

Surprising facts about TRAPPIST-1e

A year on TRAPPIST-1e lasts about six Earth days.
Its star would look deep orange-red to human eyes, with much of its energy arriving as invisible infrared light.
All seven TRAPPIST-1 planets are linked in a chain of orbital resonances, widely seen as a sign that they migrated gently inwards together early in their history.
TRAPPIST-1e is slightly smaller than Earth, but its surface gravity is estimated to be roughly 80% of ours.

Keep exploring

Sources