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.


The three planets in the habitable zone are likely facing a formidable opponent to life: high-energy particles spewed from the star. For the first time, Federico Fraschetti and a team of scientists from the Center for Astrophysics | Harvard & Smithsonian have calculated how hard these particles are hitting the planets.


Meanwhile, Hamish Hay, a graduate student in the Lunar and Planatary Laboratory, has found that the gravitational tug-of-war the TRAPPIST-1 planets are playing with one another is raising tides on their surfaces, possibly driving volcanic activity or warming ice-insulated oceans on planets that are otherwise too cold to support life.


Both Fraschetti's paper and Hay's study, "Tides between TRAPPIST-1 planets," are recently published in the Astrophysical Journal.

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