Under the general protocols of what is called “planetary protection,” this is a paramount issue and is why the Japan Aerospace Exploration Agency (JAXA) was obliged to assess the likelihood of any such biological transfers with MMX.

To make that assessment, the agency turned to a panel of experts that included planetary scientist, principal investigator, and associate professor Hidenori Genda of Tokyo’s Earth-Life Science Institute.

The panel’s report to JAXA and the journal Life Sciences in Space Research concluded that microbial biology (if it ever existed) on early Mars could have been kicked up by incoming meteorites, and subsequently traveled the relatively short distance through space to land on Phobos and Deimos.

However, the panel’s conclusions were unambiguous: the severe radiation these microbes would encounter on the way would make sure anything once living was now dead.

“In our analysis, we calculate the possibility of biology on Mars and it spreading to the moons,” Genda said. “But we did not find conditions under which more than an insignificant amount of that possible life could survive on the moons. And so there is no danger of contamination when returning a sample from the moons.”

However, he said, there is a decent chance that microbial “dead bodies” from Mars are on the surface of the moons and could – if the mission gets lucky – be drilled or scooped up for the voyage back to Earth.

The science board recommended that the mission be designated “unrestricted Earth-return” by the Planetary Protection Panel of the international Committee on Space Research (COSPAR). And last year that panel agreed with the JAXA assessment – which means there is less than a one-in-a-million chance that any living Mars microbe will exist in the sampling area on Phobos and Deimos.

In practical terms, the designation allows JAXA, and its international partners, to undertake their mission without extraordinary measures to protect the Earth and their sample on return.

In making their assessment, the JAXA-appointed panel hypothesized the potential concentration of microbes present on Mars by looking to analog environments on Earth – the Atacama Desert in Chile, as well as permafrost and dry sections of Antarctica.

Then they assessed if and how microbes in rocks in the Mars crater Zunil – where potential life would be relatively protected from deadly radiation – could be dispersed by an incoming meteorite, and then to what extent the ejecta would spread to the moons. Because they are both so close to their host planet – Phobos is the moon closest to its host planet in our solar system – they would no doubt have samples of Martian material, and perhaps of ancient Martian material when it was warmer and wetter on the planet, and had a much greater chance of being home to biology.