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 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, a team of scientists has calculated how hard these particles are hitting the planets. They found that the fourth planet -- the innermost of the worlds inside the TRAPPIST-1 habitable zone -- may be experiencing a powerful bombardment of protons. Flares on the surface of the star cause turbulence in the magnetic field, allowing the protons to sail away from the star. Where the particles go depends on how the star's magnetic field is angled away from its axis of rotation. In the TRAPPIST-1 system, the most likely alignment of this field will bring energetic protons directly to the fourth planet's face, where they could break apart complex molecules that are needed to build life -- or perhaps they could serve as catalysts for the creation of these molecules.
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