Phobos, the bigger of Mars' two moons, is pretty strange-looking. That's because its 13.6-mile (21.9-kilometer) length of its surface is scarred by a 5.6-mile-wide (9.6-kilometer-wide) scar called the Stickney Crater, a feature that some people think makes it look like the Death Star from "Star Wars."
Fortunately, at least, Phobos doesn't roam the galaxy looking for planets to destroy at the behest of a certain Jedi knight gone bad. But up until now, nobody has been able to figure out how tiny Phobos — whose surface area of 962 square miles (2492 square kilometers) is about a fifth the size of Los Angeles County — got such a big crater without being completely destroyed by the impact of whatever hit it.
But now, scientists at the U.S. government's Lawrence Livermore National Laboratory have demonstrated how a small asteroid could have smacked into the Martian moon and created a crater that takes up a substantial amount of its surface without obliterating it.
"We've demonstrated that you can create this crater without destroying the moon if you use the proper porosity and resolution in a 3D simulation," researcher Megan Bruck Syal, one of the authors of an article published in Geophysical Research Letters, said in a press release.
The study actually showed a range of possible objects and speeds that could have caused the Stickney crater. One possible scenario is the impact of an object only about 820 feet (250 meters) across — fairly humble, by asteroid standards — that was traveling at a speed of 3.7 miles (6 kilometers) per second.
Here's an animation from the researchers showing how the crater was created: