Mars germs versus Earth germs: engineering a mission to Mars

There is a lot that Nasa’s Perseverance rover has on its to-do list. Flying helicopters is only a small part of it. The rover, fitted with seven cutting-edge instruments for analysing rocks, the atmosphere and weather, is ultimately searching for signs of past and present life on Mars. But it will not do it on its own. The Perseverance mission is only the first step in a much greater project. Using its small drill, Perseverance will excavate promising pieces of Martian soil and store them in small tubes on the planet’s surface for another rover to retrieve at the end of this decade.

When the capsule carrying the coveted Mars samples eventually hits the ground somewhere in the US in the early 2030s, it will be the beginning of an operation that has not been seen since the return of the earliest Apollo missions. Whatever microorganisms there might be in the tubes will never come out alive from a high-containment facility yet to be built somewhere within a Nasa site.

“This is the most sensitive category that we have, category 5, restricted Earth return,” says Silvio Sinibaldi, who is responsible for planetary protection at Airbus Defence and Space in Stevenage. “We have brought back samples from asteroids previously, but we knew there wouldn’t be life in them. And that’s the big difference.”

Although a Nasa-led project, the European Space Agency (ESA) is an important partner in the Mars Sample Return mission, and through its participation, the European aerospace giant has won the contract to build the Sample Fetch Rover that will revisit Perseverance’s steps and collect the hidden tubes. The company will also build the Earth Return Orbiter, which will capture and bring back the sample container after its ejection from Mars.

The task of Sinibaldi’s team is to ensure that both the rover and the orbiter are designed in a way that, together with other components of the Sample Return Mission, prevents any material from Mars having direct contact with the Earth.

“You have to treat those samples as if they could cause a catastrophic event if released,” says Sinibaldi. “From the moment the robotic arm on the fetch rover collects the samples to the transfer to the ascent vehicle, we need to make sure that there is no cross-contamination, no unsterilised particles outside the bio-containment.”

It could be a humanity-destroying disease reminiscent of the plot of the 1970s thriller ‘The Andromeda Strain’ or a microbe capable of wrecking the Earth’s environment. The material inside the test tubes will be handled in a regime developed for the deadliest earthly microbes and viruses. The key, Sinibaldi explains, is breaking the chain of contact. Whatever has been directly or indirectly in touch with Mars would have to be either hermetically sealed or left behind.

For the entire Mars Sample Return mission that means a lot of clever engineering. In addition to the Sample Fetch Rover and the Earth Return Orbiter, the mission requires a Mars Ascent Vehicle and a Sample Retrieval Lander. The lander, fitted with a robotic arm, will transfer the samples collected by the fetch rover into a container embedded in the nose of the ascent vehicle. The ascent vehicle, a small rocket, will release the sealed container once in orbit around Mars. The orbiting container will then be captured by the Earth Return Orbiter and placed inside an additional safety capsule. This capsule and its contents will be the only component to survive the fiery atmospheric entry during the return to Earth, its outer shell sterilised by the high temperatures during the process.

Before the Covid-19 pandemic brought life on Earth to a standstill, a group of Nasa experts toured some of the world’s most guarded bio-hazard facilities for inspiration ahead of the construction of the Sample Receiving Facility that will support the Mars Sample Return mission. The Porton Down Public Health England facility in Salisbury was on the itinerary. Known for research into some of the deadliest viruses such as Ebola and the Marburg virus, Porton Down is, according to the report Nasa produced after the tour, as close as one can currently get to what the ultimate Mars sample facility will look like.

Originally a secret chemical warfare laboratory, Porton Down is classed as a Biosafety Level 4 facility. Researchers working in its guarded labs use protective half suits built into sealed research cabinets when working with dangerous samples. The barrier between the outer and inner sphere can never be broken unless the samples are hermetically sealed or dead. Similarly, protective gloves are built into other cabinets. Air pressure inside the cabinets is kept lower than on the outside so that all air is always pulled in. Sample-handling protocols are stringent, as they will be at the Mars sample facility, although most astrobiologists believe that Perseverance will more likely find traces of past life rather than living microorganisms.

“The surface of Mars has a very good in situ process of completely sterilising itself,” says Professor Karen Olsson-Francis, director of astrobiology at the Open University. “The surface conditions today are very detrimental to life and it would be very difficult for anything to grow there.”

Mars hasn’t always been like this. Scientists believe that up until some three billion years ago, the planet evolved quite like the Earth and had an abundant ocean of water conducive to the emergence of simple microorganisms. Then something went wrong. Mars lost its magnetic field, its atmosphere withered away, and the ocean evaporated. But despite its arid surface, Mars still has water, locked in the ice around its poles and under the ground. That’s where microorganisms might be surviving even today.

“It wouldn’t surprise me if there were living microorganisms in the subsurface,” says Olsson-Francis. “They would be protected from the harsh UV radiation; they would be exposed to favourable pressure. There is liquid water, and we know that rocks interacting with water could potentially create an environment where microbes could persist.”

The question is whether Perseverance would be able to reach those microbes. “The Perseverance rover only has a drill that is about 6cm deep,” says Susanne Schwenzer, senior lecturer in earth science at the Open University and a member of the Curiosity Mars rover research team. “Neither Curiosity nor Perseverance get beyond the active surface that is being burnt by radiation over millions of years.”

In fact, Schwenzer added, the European ExoMars rover, now scheduled to launch in 2022, has a much better chance of finding living microorganisms, as it can drill down to a depth of two metres.

It’s not only about protecting the Earth from Mars; it’s also about protecting Mars from the Earth. In fact, astrobiologists are more concerned that some earthly bugs could hitch a ride to the Red Planet on the rovers and completely ruin the research. The rover might end up detecting life it has brought with it, its findings completely useless. Moreover, there is a small chance the invaders might colonise and take over the new environment just like many species on Earth have overtaken ecosystems that they didn’t belong to (just think about the American grey squirrels in the UK).

“When you bring a sample back, you make sure to make it safe,” says Schwenzer. “We know how to handle dangerous samples on Earth. We have done it with Ebola. But when you go to Mars, you have to interact with the environment to get your sample. And that’s why the risk of going out is higher than the risk of coming back.”

Even though the radiation on the surface of Mars is so strong it would probably destroy the newly arrived microbes, there are areas, those most likely to harbour native Martian life, where the invaders might find a hospitable ground. The rovers allowed to roam in those areas, therefore, have to arrive at Mars perfectly germ-free.

‘When you go to Mars, you have to interact with the environment to get your sample. And that’s why the risk of going out is higher than the risk of coming back.’

Sinibaldi and his team have mastered the skill of building super-clean life-searching spacecraft during their work on the ExoMars Rosalind Franklin rover. Spacecraft engineers certainly aren’t a messy bunch. All kinds of satellites are assembled by technicians in protective apparel following stringent protocols in controlled clean rooms. But the standard cleanrooms and spacecraft-building procedures only address contamination with dust particles and chemical vapours. It doesn’t matter if a spacecraft orbiting the Sun or Mercury carries germs.

“One of the first questions that we got from the project team was ‘can we assemble the rover in one of our clean rooms, where we assemble other state-of-the-art satellites’?” Sinibaldi says. “We did some tests but found that it wouldn’t work.”

The company, therefore, built a brand-new cleanroom, which too was part of the Nasa expert tour in 2019. Its walls and ceilings are made of stainless steel, which is easy to sterilise and doesn’t release any volatile organic compounds. The floor contains particles of silver to inhibit the spread of bacteria. The venting system and its grids are made from similar anti-bacterial materials. Personnel entering the cleanroom follow a strict dressing and disinfecting protocol that involves several rounds of clothing changes.

“Our bio-clean facility is a three-stage clean room,” Sinibaldi explains. “You have an air-lock, then you have a preparation area and then you have the proper bio-clean area, where the flight hardware is assembled. You can’t enter the clean biological area right from the outside. You have to go through different levels of cleaning and dressing, as well as a 45-second air shower that blows away any residual particles.”

All air is filtered through HEPA filters and pushed down from the ceiling at 12 pascals in the cleanest part of the room, blowing all contamination away to the less sensitive areas. During regular cleanings, technicians alternate between three different sterilising agents to prevent bacteria from developing resistance.

The effort invested into engineering the Stevenage cleanroom paid off. The Nasa experts praised the facility in their report, describing the cleanroom as having implemented “probably the most stringent organic and bioburden facility requirements in the world”.

Moreover, the team handed over the Rosalind Franklin rover to the European Space Agency with less than 10,000 bacteria spores, about as much as normally fits on a pinhead.

“That was very challenging,” Sinibaldi says. “Humans shed millions or billions of skin particles every 24 hours and around 20 per cent of these skin particles carry bacteria spores. And because humans built the rover, we had to prevent them from transmitting any spores on it.”

It wasn’t just the rover’s outer surface that mattered but all of its internal components as well, overall, 150m2 of germ-free surfaces, according to Sinibaldi.

“The internal components do contribute to gas exchange and thus to the final number of spores,” says Sinibaldi. “We had to make sure that every contractor worked to similarly high levels of cleanliness and delivered the components already sterilised.”

The Stevenage cleanroom will now accommodate the construction of the Mars Sample Fetch rover. Sinibaldi is already devising improvements that would make maintaining the required level of cleanliness easier.

Cleanroom personnel, for example, shouldn’t walk too fast in order not to create turbulence in the downward blowing air, which could sweep up accidental contaminants. The first changing room after entering from outdoors might get an extra annex for workers to remove their outdoor clothes to reduce the contamination inside the changing room. A few more air showers might be installed to keep even the most persistent germs at bay.