TRAPPIST-1e – a Terrestrial Exoplanet

TRAPPIST-1 e is a terrestrial exoplanet in the habitable zone of an M-type star. It is a solid, Earth-sized exoplanet orbiting within the habitable zone of the ultracool dwarf star TRAPPIST-1, 40 light-years away in the constellation Aquarius. This system of seven rocky worlds–all of which have the potential for water on their surfaces–is an exciting breakthrough in the search for life on other planets.

It was one of seven new exoplanets discovered orbiting the star using Spitzer Space Telescope observations. It has a mass of 0.692 Earths, takes 6.1 days to complete one orbit of its star, and is located 0.02925 AU away from it. Three of the seven are in the habitable zone (e, f, and g). TRAPPIST-1e has the same mass, radius, density, gravity, temperature, and stellar flux as Earth. It has also been confirmed that it has a compact atmosphere, similar to the terrestrial planets in our solar system.

Researchers determined in November 2018 that of the seven exoplanets in the multi-planetary system, TRAPPIST-1e has the best chance of being an Earth-like ocean planet and is the most worthy of further study in terms of habitability. TRAPPIST-1e is one of the most potentially habitable exoplanets discovered so far, according to the Habitable Exoplanets Catalog.

Physical characteristics

Mass, radius, composition, and temperature

TRAPPIST-1e was discovered using the transit method, in which the planet blocked a small percentage of the light from its host star as it passed between it and Earth. This allowed scientists to calculate the planet’s radius to be 0.910 R☉, with a small margin of error of about 166–172 km. Transit-timing variations and advanced computer simulations aided in determining the planet’s mass, which was determined to be 0.772 M☉. Scientists could accurately calculate TRAPPIST-1e’s density, surface gravity, and composition after determining its radius and mass with low error margins.

TRAPPIST-1e is unique in its system because it is the only planet with a pure rock-iron composition and has a higher density than Earth. It has a density of 5.65 g/cm3, which is approximately 1.024 times the density of Earth (5.51 g/cm3). TRAPPIST-1e’s higher density implies an Earth-like composition and a solid rocky surface. TRAPPIST-1e has 93 percent of Earth’s surface gravity, the system’s second-highest.

Given an albedo of 0, the planet’s calculated equilibrium temperature is 246.1 K (-27.1 °C; -16.7 °F). However, for a more realistic Earth-like albedo, this provides an unrealistic picture of the planet’s surface temperature.

Host star

TRAPPIST-1, a (late M-type) ultracool dwarf star, orbits the planet. The star has a mass of 0.089 M☉, which is close to the threshold between a brown dwarf and a low-mass star, and a radius of 0.121 R☉. It is 7.6 billion years old and has a temperature of 2,516 K. The Sun, on the other hand, is 4.6 billion years old and has a temperature of 5,778 K. The star has a metallicity ([Fe/H]) of 0.04 or 109 percent of the solar amount.

The apparent magnitude of the star, or how bright it appears to us from Earth, is 18.8. As a result, it is far too dim to see with the naked eye.


TRAPPIST-1e has a close orbit around its host star. A full rotation around TRAPPIST-1 takes only 6.099 Earth days (146 hours). It orbits the Sun at a distance of 0.02928285 AU or just under 3% of the distance between Earth and the Sun. Mercury, the closest planet in our Solar System, orbits the Sun at a distance of 0.38 AU in 88 days. TRAPPIST-1e, despite its close proximity to its host star, receives only about 60% of the starlight that Earth receives from the Sun due to the low luminosity of its star.


TRAPPIST-1e has been confirmed to have a compact, hydrogen-free atmosphere similar to that of our Solar System’s rocky planets, raising the prospect of habitability even further. Hydrogen is a powerful greenhouse gas, so if there was enough to be easily detected, TRAPPIST-1e’s surface would be inhospitable.