When exploring other planets and celestial bodies, NASA missions are required to abide by the practice known as “planetary protection“. This practice states that measures must be taken during the designing of a mission to ensure that biological contamination of both the planet/body being explored and Earth (in the case of sample-return missions) are prevented.
Looking to the future, there is the question of whether or not this same practice will be extended to extra-solar planets. If so, it would conflict with proposals to “seed” other worlds with microbial life to kick-start the evolutionary process. To address this, Dr. Claudius Gros of Goethe University’s Institute for Theoretical Physics recently published a paper that looks at planetary protection and makes the case for “Genesis-type” missions.
When you have a Mars mission that is designed to search for life or life-friendly environments, it would be several shades of awkward if something biological was discovered — and it ended up being an Earth microbe that clung on for the ride. Beyond that, there’s the worry that an Earth microbe could contaminate the planet’s environment, altering or perhaps wiping out anything that was living there.
“We have a long-term programme at ESA – and also NASA – to regularly monitor and evaluate biological contamination in cleanrooms and on certain type of spacecraft,” stated Gerhard Kminek, ESA’s planetary protection officer. “The aim,” he added, “is to quantify the amount of biological contamination, to determine its diversity – finding out what is there using gene sequence analysis, and to provide long-term cold storage of selected samples.”
The process isn’t perfect, ESA admits, but the biological contamination that these scrutinized missions have is extraordinarily low compared to other Earthly manufacturing processes. There is, in fact, an obligation on the part of space-faring nations to keep planets safe if they signed on to the United Nations Outer Space Treaty. (That said, enforcement is a tricky legal issue as there is no international court for this sort of thing and that would make it hard to levy penalties.)
Spacefaring nations have international standards for biological contamination limits, and they also must monitor the “impact probability” of an orbital spacecraft smacking into the planet or moon below when they do maneuvers. Sometimes this means that spacecraft are deliberately crashed in one spot to prevent contamination elsewhere. A famous example is the Galileo mission to Jupiter, which was thrown into the giant planet in 2003 so it wouldn’t accidentally hit the ice-covered Europa moon.
Moving forward to ExoMars — the Mars orbiting and landing missions of 2016 and 2018 — ESA plans to perform about 4,500 samplings of each spacecraft to monitor biological contamination. This estimate came from the number performed at NASA on the Curiosity rover, which is trundling around Mars right now. Changes in processing, though, mean the ESA checks will take less time (presumably making it less expensive.)
For the curious, yes, planetary protection protocols would also apply during a “sample return” mission where soil or other samples are sent back to Earth. While that’s a little ways off, ESA also elaborated on the procedures it takes to keep spacecraft it creates safe from contamination.
“Samples are acquired in various ways: air samplers collect a certain amount of air on a filter, while wipes dampened with ultra-pure water are run across space hardware or cleanroom surfaces. Swabs are used to sample smaller items such as payloads or electronics,” ESA stated.
“To quantify the biological contamination, the samples are then filtered onto culture plates and incubated for between seven hours and three days depending on the specific method used, to see how much turns up. Statistical analysis is used to assess the overall cleanroom or flight hardware ‘bioburden’, and check whether it falls within the required standard or if further measures are needed to reduce it.”
Sometimes a hardy survivor is found, which is scientifically interesting because investigators want to know how it made it. ESA has a database of these microbes, and NASA has records as well. In November, the agencies announced a new bacterium, Tersicoccus phoenicis, that so far has only been found in “cleanrooms” for NASA’s Mars Phoenix lander (near Orlando, Florida) and ESA’s Herschel and Planck observatories (in Kourou, French Guiana).
Curiosity at Centre of Attention During Testing Image Credit: NASA /JPL – Caltech
There have been many reports about the possibility of NASA’s Curiosity rover contaminating Mars with microbes from Earth once it lands on the Red Planet in August. The wheels, the landing procedure and the drill bits have all come under scrutiny. But what are the concerns and what safeguards are there to prevent contamination from this or other missions?
In 1967 the United Nations drew up the ‘Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Bodies.’ All countries which sign up to the treaty “shall pursue studies of outer space, including the moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination.” Every mission is given a category (I,II,III,IV or V) depending on whether it is a flyby, orbiter, lander, or Earth return mission, whether its destination is a planet, moon, comet, or asteroid and whether the destination could provide clues about life or have the potential to support Earth life. So for instance Cassini is a catagory II mission, Curiosity is classed as a IVc mission.
Every stage of a mission is carefully monitored. From construction in a sterile clean room with laminar-air-flow systems, pressurized microbial barriers and personnel wearing hoods, masks, surgical gloves, booties and protective suits called bunny suits. Components and entire spacecraft are sterilized using dry heat microbial reduction, by being enclosed in a bioshield (like a large casserole dish) and baked them in an oven at 111.7 degrees Celsius for 30 hours. For more sensitive components a low-temperature process is used. Components are placed in a vacuum and hydrogen peroxide is injected into the sterilization chamber to establish a specified vapor concentration. Thousands of samples are taken at every stage of construction and tested for spore-forming organisms, for example the Viking mission in 1975 tested more than 6000 samples in total.
Three issues have arisen with the Curiosity rover. During the landing procedure a parachute and thrusters will slow the descent before the ‘sky crane’ lowers the rover, its wheels making direct contact with the surface. Previous rovers have waited on landing platforms for days before their wheels made contact with the surface and in tests it has been shown that even a few hours exposure to Martian levels of ultraviolet can kill between 81 and 96 per cent of bacteria that may be present. So once Curiosity lands it will probably need to remain stationary for some days to minimize the risk of contamination from its wheels.
Another issue arose last year, after launch, when it was realized that a step in the planetary protection measures wasn’t adhered to during the manufacture of the rover’s drill bits. These were meant to arrive at Mars inside a sterile box, but the box was opened and the bits tested for contamination and one of the bits was attached to the drill head. This procedure strayed from earlier agreed-to protocols. The drills have now become another cause concern as it has been found that Teflon and molybdenum disulfide from seals within the drill assembly could rub off and mix in to contaminate samples excavated during operation, making the samples more difficult to analyze. The MSL team are looking at ways to work around the problem, these could include running the drill on a slower, less percussive setting or dispensing with the drill altogether and relying on Curiosity’s scoop to take soils soil samples and using the rover’s wheels to roll over and break open rocks.
This all serves to highlight the importance of the planetary protection treaty to ensure we do everything possible to reduce the risk of contaminating other worlds and of compromising any data we return.