Trappist 1 is a star in the constellation Aquila. It is an M-type main-sequence star with a mass of 0.085 solar masses and a radius of 0.121 solar radii. It has a surface temperature of 2550 K and is estimated to be about 7.6 billion years old. Trappist 1 is one of the least massive stars known to host planets. In May 2016, the discovery of seven Earth-sized exoplanets orbiting Trappist 1 was announced, three of which are in the habitable zone where liquid water could theoretically exist on their surfaces.
Trappist 1 was first identified as a possible planetary system by astronomers using the TRAPPIST telescope at ESO’s La Silla Observatory in Chile. The team led by Michaël Gillon used the transit method to detect the faint dipping of Trappist 1’s brightness as planets passed in front of it from our perspective here on Earth. Follow-up observations were made with other telescopes, including NASA’s Spitzer Space Telescope, confirming the presence of seven planets around this ultra-cool dwarf star just 40 light-years away from Earth.
The initial discovery was based on 60 days worth of data from TRAPPIST; however, subsequent analysis revealed that some transits observed during that campaign were not caused by planets but rather by stellar activity related to sunspots on Trappist 1’s surface rotating into and out of view. After removing these false positives, the researchers were left with 22 potential transit events caused by planets over 154 days worth of data — enough to confidently say that there are multiple worlds orbiting this nearby star!
The new world (or worlds) causing these regular dips in brightness became known as TRAPPIST-1b, c, d, e, f, g and h — with “b” being closest to its parent star and “h” farthest away (see image). Based on follow-up observations conducted using ground-based telescopes including ESO’s Very Large Telescope (VLT), astronomers determined that all seven are roughly terrestrial worlds similar in size to Earth but much closer together — so close that if you were standing on one planet’s surface you could often see neighbouring ones looming large in your sky!
The innermost six orbit their host star within 20 days while TRAPPIST-1h needs 37 days for one complete revolution; all seven take less than 50 days total making them some shortest period planets found thus far outside our own Solar System! Moreover given how close they are together it is thought likely that their orbits have become synchronized such each always presents the same face towards its neighbour resulting what would be permanent day or night sides depending upon position relative to their star!