Variable X-ray flux may explain variable helium escape from the habitable-zone exoplanet LHS 1140b
A central goal in exoplanet science is to understand the conditions under which potentially habitable worlds retain atmospheres. This question is of special interest for worlds orbiting M stars, whose habitable-zone planets are more readily observable, but which also emit prolonged high-energy radiation that can erode planetary atmospheres. For one such world, LHS 1140b, a rocky planet orbiting in the habitable zone of an inactive star, time-variable helium absorption has been observed as the pl…