A deltalike fan in Jezero crater shows where water would have flowed into the lake-filled crater, transporting clay minerals and, possibly, organic molecules.


Jezero crater most popular scientific target on Mars for NASA’s 2020 rover

Update: Following closed afternoon meetings at the conclusion of a scientific advisory session on 10 February, NASA announced the official final 3 sites under consideration for the Mars 2020 rover. As expected, Jezero and Northeast Syrtis were put forward. But rather than forwarding along Eberswalde or Mawrth Vallis, two other top candidates, the 2020 rover team stated that Columbia Hills, a site previously explored by the Spirit rover, would be considered as the third option.

Here is our initial story:

Mars scientists have spoken, nominating Jezero crater and three other sites as their favorite targets for a NASA rover to be launched in 2020. Once home to an ancient river delta, Jezero crater may have collected and preserved ancient organic molecules that flowed in from beyond the crater’s rim.


The tally, taken today at the end of a 3-day meeting of 172 scientists in Monrovia, California, exposed a debate about the merits of sampling ancient deltas similar to the promising terrain in Gale crater currently being explored by the Curiosity rover, versus those who would prefer to visit rocks that formed in hot springs and may have harbored underground life.

The clear top candidate was Jezero crater. It was followed by Northeast Syrtis, a nearby carbonate-rich site home to ancient, water-associated clays that could be tied to potential hydrothermal springs. Both spots sit close to old volcanic rocks, another important goal for a mission that will collect samples that may ultimately be returned to Earth. Eberswalde crater, home to another clay-rich delta, came in third, followed by Mawrth Vallis, another potential hot spring site.

A voyage to Jezero crater, with clear evidence of an ancient delta visible from orbit, would ultimately show whether or not an early, wet surface could support life, Munir Humayun, a planetary scientist at Florida State University in Tallahassee who serves on the mission’s return sample science board, said at the meeting. They would be building off experience with Curiosity, armed with some sense of what clays to target. “If we don’t find a biomarker at Jezero,” he said, “then we’ll really be showing that a surface biosphere did not exist at Mars.”

Credits: (Graphic) Val Altounian/Science; (Data) NASA/JPL/University of Arizona

But other scientists favor a destination containing rocks that were formed in underground, hot spring environments. Subsurface life “is a model that needs to be considered for Mars,” says Bethany Ehlmann, a planetary scientist at the California Institute of Technology in Pasadena, who supports the Northeast Syrtis site. Life is found throughout Earth’s deep and extreme underground environments, and the Mars research community is now seriously considering how such biosignatures could be detected by the 2020 rover, she says.

The vote is purely advisory. NASA project scientists and engineers will decide on a final recommendation of three or four targets, also considering safety factors such as the difficulty of landing in a rocky site. Prior to the vote, the NASA team gave a quick insight into their thinking, naming three sites as clear candidates for further study: Jezero, Mawrth, and Northeast Syrtis, with Jezero the only unanimous decision. Mars scientists will hold more workshops focused on the three or four finalists, with a final site selection not expected for a year or more.

The $2 billion Mars 2020 rover has the ultimate goal of drilling some 30 pencilwide rock cores that would then be cached on the planet’s surface and, ultimately, returned to Earth for analysis. The means of return are not yet determined, but would require subsequent missions.

Correction, 12:34 p.m., 2/12/2017: The meeting discussed in the Update at the top of story occurred 10 February, not 11 February.