A flat rock with pale, veiny fissures could be the first thing the Mars rover Curiosity drills for a sample of the Red Planet, NASA scientists said Tuesday. It’s the most challenging task yet for the intrepid car-sized rover (after its landing). No spacecraft has ever penetrated a rock on Mars.

The drill is a cornerstone of the mission, able to breach the surface of interesting-looking rocks and determine what their insides contain. It can drill about 5 millimeters into Mars, which is enough to get some aspirin-tablet sized samples of dust for the rover's instruments to ingest. The goal is to find out whether Mars could have ever been hospitable for life, and understanding the formation of Mars rocks will help answer that question.