TRAPPIST-1: May 2019

The TRAPPIST-1 system has 7 known terrestrial planets arranged compactly in a mean-motion resonant chain around an ultra-cool central star, some within the estimated habitable zone.

Three of the seven rocky planets (e, f, and g) in TRAPPIST-1 system orbit in the habitable zone of the host star. Therefore, water can be in liquid state at their surface being essential for life.

The James Webb Space Telescope (JWST) will offer the first opportunity to characterize terrestrial exoplanets with sufficient precision to identify high mean molecular weight atmospheres, and TRAPPIST-1's seven known transiting Earth-sized planets are particularly favorable targets.