Original sentence: The Martians need to relocate from their world because of impending planetary catastrophe: meteors bombard the planet (the so-called Martian canals are actually linear cities, which makes them thinner targets), and the moons Phobos and Deimos may crash to the surface
Edited sentence: The Martians need to relocate from their world because of impending planetary catastrophe: meteors bombard the planet (the so-called Martian canals are actually linear cities, which makes them thinner targets), and the moons Phobos and Deimos threaten to crash to the surface