Choosing a place to land NASA's next Mars rover

With two rovers currently operating on Mars, NASA has begun the search for where its next Mars rover will go. And a lot is riding on the site selection because this rover, unlike previous ones, will collect and store samples of rock and soil for eventual return to Earth.

"The next 20 years of Mars exploration hinges on where this rover goes," says Philip Christensen, planetary scientist in Arizona State University's School of Earth and Space Exploration on the Tempe campus. "It has to tell us something fundamental about the broader history of Mars." He was quoted in a story in Nature about the new landing site search.

NASA's goals for the new mission require a landing site that contains an environment where life could have existed. The site must also have a geology that could preserve potential "biosignatures" – unmistakable traces of life. And the site must be trafficable to let the rover land safely and drive to the relevant rocks and soils to collect samples.

The new rover, which will join working rovers Opportunity (which landed in 2004) and Curiosity (2012), has not yet been given a name. Scientists are just calling it Mars 2020, or M2020 for short. The plan is to build a machine nearly identical to Curiosity and equip it with fresh instruments to probe the Martian surface.

To begin the process of sifting through candidate landing sites, more than 100 planetary geologists gathered May 14-16 in Arlington, Virginia. Launch for the new rover is set for July-August 2020, with arrival on Mars in February 2021. The rover's baseline mission will last one Martian year, or 1.9 Earth years.

At the workshop, a total of 27 candidate sites were presented, discussed, and critiqued. At the end of the meeting, the scientists ranked the candidate sites according to their scientific value for reaching the mission goals.

But this ranking won't be the last word by any means. The choice of Gale Crater for the Curiosity rover came only after more than 65 sites had been examined during five workshops held from 2006 to 2011. The next M2020 site workshop will be in summer 2015, and the final site may not be selected until 2019. Meanwhile, scientists are collecting more data and images on the sites proposed at this meeting. If the past is any guide, at least a few new candidates will emerge by mid-2015.

At this first meeting Christensen, together with several colleagues at other institutions, proposed a landing site in Margaritifer Terra that's rich in salts and clays, both good for preserving biosignatures. Another ASU Mars scientist, Steve Ruff, advocated a return to an already-visited site in Gusev Crater with hot-spring deposits. And ASU postdoc researcher Mark Salvatore presented the case for yet a third site, in Kashira Crater, also clay-rich and located in Margaritifer Terra.

NASA’s plan for bringing back Martian samples is ambitious, involving a trio of missions over many years. M2020 is step one: it will 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 a "fetch rover" to get the cached samples and then blast them into orbit. Finally, step three would capture that Mars-orbiting package and fly it back to Earth.