The first spacecraft to collect Martian rocks for eventual return to Earth will explore Jezero crater, NASA announced on 19 November. Jezero is a 45-kilometre-wide crater that was once filled with water, where Martian life could have thrived.

“Getting samples from this unique area will revolutionize how we think about Mars and its ability to harbour life,” says Thomas Zurbuchen, NASA’s associate administrator for science, who chose Jezero over three other finalists .

Still undecided is whether the rover would embark on a long drive to a second site after it finishes surveying Jezero. Some scientists want the rover to roll 28 kilometres to a location dubbed Midway, where it could sample some of the most ancient rocks known on the red planet.

Either way, the 2020 rover will set the direction of NASA’s Mars programme for years to come, says Lori Glaze, acting director of the agency’s planetary-sciences division in Washington DC.

Rocking out

Jezero was formed billions of year ago by a meteorite impact. At one point, water filled it to a depth of about 250 metres, and then flowed out — leaving behind sediments that could contain a record of life, if any ever existed there. “You see a canyon coming in and depositing the sediment,” says Kenneth Farley, the mission’s project scientist. “That is a major attraction.”

Jezero is also home to carbonate rocks, whose chemistry could reveal how the lake’s water and the Martian atmosphere interacted in the distant past, Farley says. And a wider variety of rocks found upstream could have been swept into the crater, where the rover could study them as well.

The varied geology of Jezero and its surroundings helped Jezero to beat out other potential destinations for the 2020 rover. They include Northeast Syrtis, which contains some of the oldest rocks on Mars, and Columbia Hills, which the Spirit rover explored between 2004 and 2011.

The US$2.4-billion rover is slated to launch in July 2020 and land on Mars in February 2021. It will carry 37 sample tubes and 5 spares, which it will fill using its robotic arm — an attachment designed to drill long, slender cylinders of Martian rock. The rover will collect a variety of samples as it explores the red planet, and eventually set them down for a future mission to retrieve.

NASA has not yet developed a detailed plan for transporting the samples back to Earth. Zurbuchen says that it hopes to send a mission to Mars in the late 2020s to retrieve the rocks, and return them to Earth in the early 2030s.