Alien life likely can't survive on exoplanets smaller than Mars, scientists say

A rocky planet orbiting in the habitable zone of a sun-like star may look like a perfect place for life to thrive — but not if it's too small to hold onto its atmosphere.So, we may wonder: How much smaller Earth could be and still have its delightfully breathable atmosphere? How small could an exoplanet be to sustain life as we know it? With these questions in mind, University of California Riverside planetary scientist Michelle Hill and her colleagues recently simulated what happens to th