How Mars' moon Phobos came to look like the Death Star

LIVERMORE, Calif., Oct. 12 (UPI) -- Mars' largest moon, Phobos, is well known for its resemblance to the Death Star, the mobile space station and planet-destroying weapon from Star Wars. Now, scientists know how Phobos' unique appearance came to be.

A massive crater, spanning nearly half the moon, lends Phobos its Death Star-like appearance. Until now, astronomers couldn't figure out how an impact could leave such a sizable mark without destroying the satellite.

New simulations designed by physicists at Lawrence Livermore National Laboratory have offered some answers.

"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," Megan Bruck Syal, a researcher with the LLNL planetary defense team, said in a news release. "There aren't many places with the computational resources to accomplish the resolution study we conducted."

The models -- detailed in the journal Geophysical Review Letters -- suggest a range of size and speed combinations, but researchers believe the most likely impact scenario involved an object 250 meters, or 820 feet, across, traveling 6 kilometers per second, roughly 14,000 miles per hour.

To model the Phobos impact, Syal and her colleagues at LLNL used an open source code called Spheral. The code is being developed to simulate the outcomes of various methods for deflecting Earth-bound asteroids.

"Something as big and fast as what caused the Stickney crater would have a devastating effect on Earth," Syal said. "If NASA sees a potentially hazardous asteroid coming our way, it will be essential to make sure we're able to deflect it. We'll only have one shot at it, and the consequences couldn't be higher. We do this type of benchmarking research to make sure our codes are right when they will be needed most."