Minimum Radius for Long-Lived Atmospheres on Earth-like Exoplanets: About 0.8 R⊕, Possibly 0.6 R⊕ Under Favorable Conditions

To the point

Michelle Hill and colleagues show that rocky, Earth-like planets in the habitable zone around Sun-like stars need to be about 0.8 Earth radii to hold an atmosphere for billions of years, though under favorable conditions they could be as small as 0.6 Earth radii, with carbon dioxide supply, mantle characteristics, and volcanic activity determining whether gas is retained or replenished, and some atmospheres can be rebuilt later by impacts, meaning even small worlds could be habitable.