Why smaller planets are better at building large moons

A giant crescent moon hangs like a dim red bowl in a darkening re-clouded sky. A dark hilly landscape stretches beneath.

New simulations that describe how moons, including Earth's own moon, formed strongly imply that exomoons are more likely to be found around rocky exoplanets.

Our moon is thought to have formed when a Mars-size planetesimal called Theia slammed into Earth, gouging out a huge wound in our planet and rendering its entire surface molten. It's believed that the moon then coalesced from debris that settled into a ring around our planet.