The curious minds at What If predict what would happen if Earth collided with Mars, revealing catastrophic destruction, orbital instability, and planetary debris.

Last time a stray planetoid the size of Mars smashed into Earth, it scattered our planet's young crust into space, where gravity glued those particles into what we now call the Moon.

Charleston, SC, astronomy professor answers questions from high school students about wormholes, black holes, colonizing Mars, outer space odors and more.