As NASA continues to develop its next Mars rover, the space agency also has the important job of figuring out where to put the vehicle on the Red Planet. It’s a big decision since the future robot — known as the Mars 2020 rover — will be tasked with preparing samples of Martian dirt that could potentially be returned to Earth. So NASA wants to pick an area with a variety of different rocks and soils to study.

After years of discussion, the space agency has narrowed down the list of possible landing sites to three: Columbia Hills inside Gusev Crater, where the inactive Mars Exploration Rover, Spirit, is currently located; Jezero Crater, a region thought to be home to an ancient lake similar to Gale Crater — the home of NASA’s Curiosity rover; and NE Syrtis, an area once warmed up by ancient volcanic activity. The finalists were picked at a landing site workshop in California last week.

A crucial goal of the Mars 2020 rover is figuring out if microbial life once thrived on the Red Planet

A crucial goal of the Mars 2020 rover is figuring out if microbial life once thrived on the Red Planet. That’s why the three final landing sites all have one thing in common: they used to be watery. Since water is a crucial ingredient for life on our planet, NASA thinks it may be easier to find past signs of Martian life in regions that once had liquid H2O. Data collected from the Spirit rover revealed that hot springs flowed through Columbia Hills, and flooding may have formed a small lake in Gusev Crater. NASA also thinks that NE Syrtis’ volcanic activity once caused ice on the surface above to melt, as well as hot springs to bubble up and flow throughout the region’s crust.

Additionally, the space agency wanted a spot that the 2020 rover could easily move around in and accomplish all of its science goals. Not only will the bot be drilling and collecting dozens of samples, but it’ll be analyzing how habitable past Mars used to be, searching for the “chemical or mineral signs of past life” in Martian rocks. The rover will also assessing how hazardous it may be for humans to explore the Red Planet.

Not everyone is pleased about the three final choices

Not everyone is pleased about the three final choices, according to Nature. A few scientists are opposed to visiting Columbia Hills again, though others argue that the region is ideal because of its geological diversity and the past hot springs that flowed there. It’ll be a while before we know the final landing site though; that decision will supposedly be made a year or two before the rover’s launch in 2020 on top of an Atlas V rocket.

And even if the rover is successful in collecting samples, there are no concrete plans yet for a mission that will take the soil back to Earth. So for now, the plan for the 2020 rover is to collect a bunch of precious samples and then leave them on the surface of Mars for a future retrieval. But when and how that will happen remains unclear.