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

Rows of colorful planets of all colors and sizes over a dark background.

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?