Here's good news if you happen to drop something while you're strolling across a sandy section of Mars: You should be able to find what you dropped more easily than if you had dropped it into desert sands on Earth. And that's not just because of Mars' weaker gravity. Two teams of physicists have shown that a denser atmosphere, such as Earth's, makes a falling metal ball penetrate much deeper into grainy terrain.
"It's very counterintuitive," says Detlef Lohse of the University of Twente in Enschede, the Netherlands. "You would expect that, once air is there, there would be more friction," slowing down