In 2020 three rovers, one from the US, one from Europe and one from China will depart for Mars with a single goal; to look for past or present life on The Red Planet.

The rovers will also provide a critical step in the efforts to return samples of Martian regolith to the Earth. This would give scientists the opportunity to learn a great many more details about Mars and its habitability, since laboratories on Earth have much more sophisticated instruments than the ones riding on the rovers on Mars.

The upcoming NASA rover Mars 2020 will cache surface samples during its mission in Jezero crater, which might, if ESA and NASA can agree to it, be collected by a joint American-European mission that would return the samples to Earth in 2028.

However, according to Jorge Vago, project scientist on the ESA-rover, ExoMars (also known as Rosalind Franklin ) that will land in Oxia Planum in 2021 along with the American and Chinese rovers, it might be worth reconsidering which samples would actually be the most valuable to send back to the scientists awaiting their arrival on Earth.

“Mars 2020 will acquire samples from the surface, where ionising radiation is likely to have damaged any organic molecules. It is ExoMars, with its 2-meter depth drill and advanced organics detection instrument, MOMA, that has the best chance to make an important discovery regarding the possibility that Mars may have harbored life in its distant past. If this proves to be the case, perhaps we may need to rethink whether we should not think of bringing back well selected subsurface samples rather than those collected by Mars 2020,” Jorge Vago writes in an e-mail to rumrejsen20nu.

Jorge Vago, ESA’s ExoMars Project Scientist. Photo: ESA

Currently, NASA and ESA are studying possible ways of returning the Mars 2020 samples from Mars. ExoMars, however, does not have the capability to cache samples for a return mission later on.

“That requires a complicated setup that weighs a lot. It would have been impossible to combine our present, very capable payload with a sample caching system on the same rover. In fact, NASA’s 2020 rover has paid a dear price (compared to Curiosity’s analytical firepower) to include the caching system,” Jorge Vago writes.

Even still, he believes the samples collected by ExoMars would be of higher value could they be returned to Earth.

“The point I am trying to make is that bringing back the right samples will make all the difference. In this regard, ExoMars will be super important: Are the samples collected at depth more interesting/better preserved? We think probably yes, and once we will have investigated this, perhaps it will be time to rethink what samples to bring back to Earth.”

Besides having a longer drill than Mars 2020, Rosalind Franklin will also land in an area, Oxia Planum, that is much older than Gale Crater (3.6 billion years) that NASAs Curiosity rover is currently exploring and older than Jezero Crater (3.5 billion years) that is the targeted landing site for Mars 2020.

“The Oxia Planum clay deposits are dated at 4.1 billion years old, from the epoch when Mars’ surface was crisscrossed by plentiful liquid water systems,” Jorge Vago writes and continues:

“The ExoMars mission will be capable of securing many firsts: (1) the oldest site investigated on Mars, (2) the first exploration of the martian subsurface, (3) the most accurate geological and organic composition determination so far, and (4) the best chance yet to make (potential) biosignature detections on another planet. “

Jezero Crater, however, also shows strong evidence of once having been filled with water. It lies in the region Syrtis Major where spikes of methane have been detected by previous Mars-missions. Scientists are curious about these spikes since 95 percent of the methane on Earth is produced by lifeforms and therefore the molecule is considered a biosignature, although scientists also are quick to point out that methane can also be produced by geological processes.

As of writing, none of the agencies have made a formal decision to launch a Mars sample return mission.