Planetary geologists are set to narrow down a list of landing sites for a mission set for 2020

Credit: JPL/NASA

NASAs Curiosity rover is in the prime of its life, exploring the rocks, soil and air of Mars. But the agency is already planning its successor and this time, the scientific stakes are higher.

On 14 May, planetary geologists will gather in a hotel near Arlington, Virginia, to begin hammering out where NASA might send its next Mars rover, set to launch in 2020. The plan is to build a machine that is nearly identical to Curiosity, and equip it with fresh instruments to probe the Martian surface.

Although NASA has yet to finalize details, the next rover will almost certainly have a hugely important, unprecedented job: to collect and store rocks and soil for a future spacecraft to bring back to Earth. It would be the first ever sample return from Mars.

The next 20 years of Mars exploration hinges on where this rover goes, says Philip Christensen, a planetary scientist at Arizona State University in Tempe. It has to tell us something fundamental about the broader history of Mars.

NASAs workshop this week will discuss possible landing sites. Many look familiar: they were on the longlist of sites for Curiositys landing in 2012. Such locations include Mawrth Vallis, an ancient valley strewn with minerals formed in water, which would help with the rovers main goal of finding and exploring environments that could once have been suitable for life. The European Space Agency is also considering the site for its ExoMars rover, which will launch in 2018 (seeNature508,1920; 2014).

Other possibilities for 2020 include several ancient, now-dry lakes and deltas where flowing water once laid down sediment. These areas, including Eberswalde Crater, were among the top candidates for the Curiosity mission. They were passed over in favour of Gale Crater, where the rover is laboriously trekking towards a 5-kilometer-high mountain of sediments. Curiosity has yet to detect concentrated amounts of organic material, but the rich river-laid sediments in Eberswalde are likely to offer that bounty, says geologist Ross Irwin of the Smithsonian Institution in Washington DC.

The 2020 rover will also have the crucial extra task of collecting samples. Scientists have talked for decades about getting their hands on Martian rocks to look for signs of past life. They have studied meteorites that originated on Mars, but no space agency has yet been able to bring back samples directly, in part because of the cost and in part because of technical failures (seeNature479,275276; 2011).

NASAs plan for bringing back Martian samples would involve a succession of missions over many years (see Fetch!). Step one would need a rover to collect and store roughly 30 narrow cylinders of rock and soil, either on board or on the ground. In step two, an unmanned rocket would fly to Mars and deploy another rover to fetch the samples and then blast them into orbit. Step three would be to capture that orbiting package and fly it back to Earth.

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NASA Plans Mars Sample-Return Rover