After three days of lively debate last week in Glendale, California, 158 scientists and Mars enthusiasts voted on the best landing and research site for the Mars 2020 Rover, leaving with a virtual tie.

NASA’s Science Operations Team Chief Sarah Milkovich summed up the room in a tweet this way:

“On a slightly confusing note, we’re done!”

The fourth-and-final workshop brought to a close a four-year process recommending a single landing site for the Mars 2020 rover to NASA headquarters in Washington, D.C. From an original list of 30 sites, four candidates qualified for this three-day round of scrutiny: Columbia Hills, Jezero Crater, Northeast Syrtis, and Midway.

Map of final four Mars 2020 landing sites
Jezero Crater and NE Syrtis are 37 kilometers apart, while Midway is about 28 kilometers from Jezero Crater.

The Mars 2020 mission aims to learn about the history of Mars’ environment, look for evidence of past life (which will inform whether future life could reside there), take samples that may one day be returned to Earth, and take measurements in preparation for a crewed mission.

Why A Mega-Mission Is More Likely Than Ever

Workshop attendees voted online, rating each potential site on a scale of one to five (one indicating low potential and five indicating high potential) based on three criteria. Voters filled out this criteria based on the primary mission for the first 1.25 Mars years, as well as for the extended mission afterward for a total of six criteria per site. The votes were averaged across each site per criterion.

The first criterion rated the potential to unveil fundamental scientific discoveries about Mars’ formation or potential life. The second evaluated the potential usefulness of a humankind’s first returnable cache of Mars soil. Finally, the third evaluated confidence that various research and evidence supported criterion one and two.

Chart of vote results
The final results from 158 votes. Although there were 226 attendees on day one, some people couldn't stay for the final vote.

By the numbers, NE Syrtis barely edged out Jezero Crater for the prime mission. But for the extended mission, #teamJezero scientists will be pleased to know that Jezero Crater and Midway tied as most promising, significantly ahead of NE Syrtis. For now, it’s unclear which site the rover will claim as home (although we’re probably not headed to Columbia Hills, since Spirit already scoped it out).

But since Midway, as the name implies, lies between the 37 kilometers separating NE Syrtis’s evidence of mineral springs and Jezero Crater tempting delta, the rover team may consider a mission that visits Midway and one of the other sites to capture the best of both worlds.

Plus, the prospect of returning samples (with tubes small enough to be mistaken for a laser pointer at the workshop) is an objective that’s been on the minds of the National Research Council for 30 years. These would be the first samples returned to Earth, but in the ultimate game of delayed gratification, the process of returning them spans multiple missions. Scientists must balance optimizing for sample return versus maximizing the surface science the rover can perform.

Shannon Cofield, sedimentologist from Old Dominion University and #teamJezero, points out that NE Syrtis and Midway are quite similar. On the other hand, Jet Propulsion Lab research scientist, Bethany Ehlmann makes the case that Midway and NE Syrtis are the only sites that align with the goals of the Decadal Survey compiled by the National Academy of Sciences.

What Comes Next

Upon sending the results to NASA Headquarters, the Mars 2020 team and Thomas Zurbuchen, NASA’s Associate Administrator of the Science Mission Directorate, will make the final decision, scheduled to be announced by the end of the year.

Powered by an Atlas V-541 launch vehicle from United Launch Alliance, the $2.5 billion Mars 2020 rover will launch from Cape Canaveral Air Force Station, Florida, in July 2020 with hopes to reach Mars by February 2021.