NASA and the European Space Agency (ESA) are teaming up to return a sample of Martian material to Earth in the 2030s, but that has provoked fears in some quarters that we could be bringing back more than just rock and air. Could we also inadvertently contaminate Earth's biosphere with Martian microbes?
The scientific desire for a Mars sample return is clear. The Moon rocks returned to the Earth by the Apollo astronauts over half a century ago are still studied to this day and are a treasure trove of invaluable information about the Moon's composition, history and formation.
And while we've had a permanent presence on the Martian surface for 25 years now, scientists are keen to study pristine pieces of Mars in the lab. After all, our laboratories on Earth are far more advanced than anything we can squeeze into a rover. Samples can also be kept back to be analysed by even more advanced technology in the future.
Sample recovery
The plan is to dispatch two courier spacecraft to Mars in the late 2020s to collect samples of Mars's rocks, soil and atmosphere gathered up by the Perseverance rover currently trawling the Martian surface. One spacecraft would land nearby and transfer the samples over from Perseverance. It would then launch into Mars orbit to rendezvous with the second spacecraft, which would then transport the samples back to Earth sometime in the early 2030s.
But what are the chances they'll bring back more than they bargained for?
“The question of whether samples from Mars could present a hazard to Earth’s biosphere has been studied by several different panels of scientific experts... over the past several decades,” NASA says.
“The reports from these panels have found an extremely low likelihood that samples collected from areas on Mars, like those being explored by Perseverance, could possibly contain a biological hazard to our biosphere."
The agency points to the fact that Earth is regularly hit by meteorites from Mars and there's no evidence of any subsequent contamination.
According to an ESA report, the probability that a single unsterilised particle bigger than 0.0002 millimetres across will be released into the Earth environment by a sample return is less than one in a million. That's any particle from Mars - the chances of that particle being biological are significantly lower as we don't even know if there is any life on Mars.
The chances are so low because NASA and ESA are putting in place a series of stringent steps to reduce the risk as much as possible. For starters, they'll only collect material from the first few centimetres of the Martian surface. This surface material is extremely dry and bombarded by intense radiation from the Sun. If there is microbial life on Mars, it is unlikely to reside there as it would be quickly sterilised.
Multi-layered containment
“The planned approach would provide higher levels of isolation than anything achieved previously in space fight, including for the samples of lunar rocks, comet dust, asteroids, and the solar wind successfully captured and returned to Earth by earlier NASA and international missions,” NASA says.
Once the sample reaches Mars orbit, it will enter the Capture, Containment and Return System (CCRS). It will be sealed inside the first of two containment vessels, while being heated to sterilise any stray Martian dust. Only then will it enter a so-called 'clean chamber', which is then sealed for its trip back to Earth.
Then it's all about ensuring the whole thing remains sealed until scientists can access the samples in carefully controlled labs here on Earth. The CCRS is fitted with a shield to protect it from micrometeorites, which could puncture the seal on the return trip. Even the route home has been carefully considered.
“The trajectory of the return orbiter... would be pointed away from Earth until a few days before the planned landing, allowing a final decision to be made about proceeding with Earth entry using all available information collected during the entire mission,” NASA says.
Rigorous pre-flight tests will ensure the probe will be able to withstand the searing temperatures and crippling G-forces of atmospheric re-entry. Then it's hazmat suit time.
“Out of an abundance caution, the entry system and its samples would be treated with the highest level of care once having landed, as if they could be hazardous biological materials,” NASA says.
It will quickly be encased in yet more containing layers for transport to a dedicated Mars sample receiving facility. Only then will scientists be able to assess their hard-won treasure and start discovering the unique insights into Mars that it will provide.
So, while the risk to Earth's biosphere is not zero, NASA and ESA seem confident that they've put the necessary steps in place to make contamination as close to impossible as it is possible to be.
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