NASA Will Zap Mars Sample Contamination With Powerful UV Before Returning to Earth

As part of NASA’s ambitious Mars Sample Return (MSR) endeavor, work is ongoing to ensure the collection of Martian samples and their journey to Earth meet the required safety standards, agency officials said during a meeting last week (October 20).

Currently, the plan to bring samples of Martian terrain back to Earth involves sending a retrieval lander to rendezvous with the Perseverance rover. The lander will then use its robotic arm to pick up tubes of samples that were packaged and dropped off by the Perseverance rover, which has been busily collecting rock samples near the Jezero Crater since 2021, and place them in an attached container.

This will be done by opening a small door on the lander, which allows access to the orbiting sample (OS) container. The door will remain open for about 60 hours so that the tubes can be carefully placed inside, Brian Clement, an environmental microbiologist at NASA and MSR’s planetary protection systems engineer, explained at a session held during the Fall 2023 Meeting of the National Academies of Sciences, Engineering and Medicine’s Committee on Planetary Protection.

“It’s when that door is open that we are concerned with dust particles accumulating on the exterior of the OS,” Clement said

The MSR program is considered a “Restricted Earth Return” mission, which means that the samples must be contained and protected throughout the entire collection process and the return journey to Earth, as part of the mission’s objectives are to determine if Mars might harbor subterranean microbial life. To keep the containers safe, dust contamination on flight hardware — the exterior of the OS — must be limited, scientists say. To accomplish this, the OS will be sterilized in orbit. When the OS is back in Martian orbit, it will be captured by another orbiting spacecraft that will first sterilize it with very strong doses of ultraviolet (UV) radiation before ferrying it on the return journey to Earth.

The “overkill sterilization” process

This process may take 15 to 20 days in orbit, while the collected 500 grams of Mars samples will remain sealed inside multiple layers of protection. The various layers “protect us from isolated failures,” Clement said. “That’s really the key piece here.”

The “overkill sterilization” process involves such an extreme dose that will kill even the most resistant organisms in the dust particles attached to the OS exterior.  “It is generally understood that this is the approach one takes in the biomedical space when you don’t know the number of organisms that you’re targeting,” Clement said.

That way, researchers can be certain that the samples they’re studying — and anything of scientific value — came from the precise sample site Perseverance scooped or dug it up from, not from wherever the outside dust happened to blow in from. Clement added that work is ongoing to determine the best materials and coatings for the OS such that thorough UV treatment of every dust particle on the surface can be ensured without destroying the samples stored inside.

It is also possible that a few free-flying dust particles may also launch into orbit when the rocket-powered OS lifts off the Martian surface. Since those particles could contaminate the dust-free earth return orbiter, invoking a solar UV sterilization method is important so that “these particles are mitigated in Mars orbit,” Clement said. That way, everything that makes it back to Earth can be assumed to be sterile, removing possible sources of error or confounds during scientific analysis.

Once the OS is free of dust contamination, it would be placed into a secondary containment vessel for return flight to Earth.

The current plan is to land the samples in a 150 square-mile- (388 square kilometers) region in the US Department of Defense’s Utah Test and Training Range. There, previous drop tests have shown that the flat, soft, sandy clay ground will naturally cushion the landing, helping preserve the collected samples intact. The same location received samples from the near-Earth asteroid Bennu last month.

After touchdown, a different team will take on the post-mission efforts to ensure the samples are contained according to planetary protection regulations while also preserving them for science, Clement said. According to initial estimates, the MSR program would cost a total of $4 billion and launch to Mars in 2027. An independent review board, however, recently concluded that the program will likely cost $8 billion to $11 billion. That mission launch would happen no earlier than 2030 — a delay of three years from the mission’s original timeline.