Since its discovery in 2016, planetary scientists have been excited about TRAPPIST-1, a system where seven Earth-sized rocky planets orbit a cool star. Three of the planets are in the habitable zone, the region of space where liquid water can flow on the planets’ surfaces. But two new studies by scientists in the University of Arizona’s Lunar and Planetary Laboratory may lead astronomers to redefine the habitable zone for TRAPPIST-1.