NASA/JPL-Caltech

When you think about fossils, you probably imagine T. rex skulls and sauropod femurs. NASA's Mars 2020 rover will be looking for fossils on Mars, but not that kind of fossil.

NASA highlighted a new study in the journal Icarus this week that points out some fascinating formations around the inner rim of Jezero Crater, the rover's planned landing site. The agency likens these concentrated carbonate mineral deposits to a bathtub ring around what had once been a lake 3.5 billion years ago.

Enlarge Image NASA

"On Earth, carbonates help form structures that are hardy enough to survive in fossil form for billions of years, including seashells, coral and some stromatolites -- rocks formed on this planet by ancient microbial life along ancient shorelines, where sunlight and water were plentiful," NASA said.

NASA doesn't expect to find seashells, but the rover will take a close look for stromatolites. Scientists would be thrilled to discover signs of past microbial life on the currently inhospitable planet. The rover's investigation of the carbonate deposits might also tell us more about how Mars transitioned from a watery place to a barren one.

The Mars 2020 rover is coming together at NASA with a launch planned for the middle of next year. If it stays on schedule, then the rover will arrive at the crater in February 2021.

Scientists don't know if the carbonates formed from the ancient lake or if they might've been deposited earlier. We'll have to wait to learn more. It'll be a landmark worth looking forward to.