TRAPPIST-1

TRAPPIST-1 is an ultra-cool red dwarf star with seven known planets. It lies in the constellation Aquarius approximately 40.66 light-years away from Earth, and it has a surface temperature of about 2,566 K (2,290 °C; 4,160 °F). Its radius is slightly larger than Jupiter's and it has a mass of about 9% of the Sun. It is estimated to be 7.6 billion years old, making it older than the Solar System. The discovery of the star was first published in 2000.

Observations in 2016 from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) at La Silla Observatory in Chile and other telescopes led to the discovery of two terrestrial planets in orbit around TRAPPIST-1. In 2017, further analysis of the original observations identified five more terrestrial planets. It takes the seven planets between about 1.5 and 19 days to orbit around the star in circular orbits. They are all likely tidally locked to TRAPPIST-1, and as such it is believed that each planet is in permanent day on one side and permanent night on the other. Their masses are comparable to that of Earth and they all lie in the same plane; from Earth, they are seen to pass in front of the star. This placement allowed the planets to be detected: when they pass in front of the star, its apparent magnitude dims.

Up to four of the planets—designated d, e, f and g—orbit at distances where temperatures are likely suitable for the existence of liquid water, and are thus potentially hospitable to life. There is no evidence of an atmosphere on any of the planets, and observations of TRAPPIST-1b have in particular ruled out the existence of an atmosphere. It is unclear whether radiation emissions from TRAPPIST-1 would allow for such atmospheres. The planets have low densities; they may consist of large amounts of volatile materials. Due to the possibility of several of the planets being habitable, the system has drawn interest from researchers and has appeared in popular culture.