TRAPPIST-1: A Cool Red Dwarf and Its Seven Worlds

TRAPPIST-1 is an M8.0 V star, making it a small, cool red dwarf. It has a mass of 0.0898 solar masses, a radius of 0.119 solar radii, and a temperature of 2570 K, all of which are smaller or cooler than the Sun. Its age is 7.6 billion years. Seven planets orbit this host.

TRAPPIST-1 b and TRAPPIST-1 c were discovered in 2016. TRAPPIST-1 b is an Earth-like planet with a radius of 1.12 Earth radii, larger than Earth's, a mass of 1.37 Earth masses, and an orbital period of 1.51 days. TRAPPIST-1 c is also Earth-like, with a radius of 1.1 Earth radii, larger than Earth's, a mass of 1.31 Earth masses, and a period of 2.42 days.

Also discovered in 2016, TRAPPIST-1 d is a Sub-Earth with a radius of 0.788 Earth radii, smaller than Earth's, a mass of 0.388 Earth masses, and a period of 4.05 days. In 2017, TRAPPIST-1 e was found, a Sub-Earth with a radius of 0.92 Earth radii, a mass of 0.692 Earth masses, and a period of 6.1 days.

The remaining three planets were also discovered in 2017. TRAPPIST-1 f is Earth-like with a radius of 1.05 Earth radii, larger than Earth's, a mass of 1.04 Earth masses, and a period of 9.21 days. TRAPPIST-1 g is Earth-like with a radius of 1.13 Earth radii, larger than Earth's, a mass of 1.32 Earth masses, and a period of 12.4 days. TRAPPIST-1 h is a Sub-Earth with a radius of 0.755 Earth radii, smaller than Earth's, a mass of 0.326 Earth masses, and a period of 18.8 days.

Among the listed planets, TRAPPIST-1 b has the shortest year at 1.51 days, while TRAPPIST-1 h has the longest at 18.8 days. TRAPPIST-1 g has the largest radius at 1.13 Earth radii, and TRAPPIST-1 h has the smallest at 0.755 Earth radii. TRAPPIST-1 b has the largest reported mass at 1.37 Earth masses, and TRAPPIST-1 h has the smallest at 0.326 Earth masses.