Re: why doesn't venus have any moons?

Dear Miss Sylvia,
Of the four rocky inner planets, only Earth and Mars have moons. Based on four centuries of telescopic observations, crewed missions, and robotic explorers, we think that our moon was formed when a huge body a few times the size of Mars careened into the earth 4 billion years ago. The debris from that titanic crash coalesced under its mutual gravity to form our moon. Which, by the way, is drifting ever so slowly further and further away from us, slightly slowing our Earth's rotation as it does so. (See the Mad Scientist archives for more information. Moderator)

Mars' two moons, Phobos and Demos, appear to be asteroids which came close enough to Mars eons ago to be captured into orbit around the red planet.

So why don't Venus and Mercury have moons? Because they've never been hit with a large enough asteroid nor had moon-sized asteroids zip by close enough to be captured by their gravity. Does it sound like chance or luck plays a role in whether a planet ends up with moons? Yes, it certainly does! Many phenomena in nature are "probabilistic"; the future is like rolling cosmic dice. And that's what make science so interesting and fun- you never know for sure what's going to happen next. Have a great life and keep your eyes on the stars.

Jim Foerch
James C. Veen Observatory
Lowell, Michigan, USA