Clandestine agents and heroic citizens of blockbuster sci-fi movies are often portrayed as defending the Earth from the alien miscreants of the Universe. Blasting slimy green extraterrestrials might be great cinema, but it doesn’t always represent the shrewdest of scientific moves. That’s because whilst the chances of ne’er-do-well space-faring aliens wandering around our towns and cities can be safely relegated to science-fiction, the reality is that it’s the Universe, not us, that needs defending from visitors from Earth.
So how do we clean our spacecraft when we send them out into space? To answer that question here’s the result of an interview I did with NASA’s Planetary Protection Officer a few months ago. This concern is particularly relevant given the current mission of NASA’s Phoenix Mars lander and that of the Mars Exploration Rovers, who are studying locales on the Red Planet that might be hospitable to life.
Ever since the first robotic missions to the planets we’ve also been inadvertently sending small amounts of microbes up there too. It wasn’t until the last few decades (when we began scouting for microbial life elsewhere in the Solar System) that this started to become a major headache for space agencies around the globe. The last thing we want to do in our search for life in the Solar System is discover the disastrously familiar sign of life which has piggybacked its way millions of kilometres from Earth.
Spirit & Opportunity were only allowed to take a certain level of spores with them. Courtesy: NASA/JPL/Caltech.
Today the responsibility for keeping NASA’s spacecraft clean (and in some ways protecting any alien life in the Solar System) falls on its Planetary Protection Officer Dr Catharine Conley. Her job is to see that NASA spacecraft are kept free from microbes from Earth that might be spread into space by our space-faring endeavours…well almost. It might surprise you that already we’ve let countless microbial ‘spores’ into the Cosmos. “There were probably viable spores on spacecraft that were launched over the past few decades, however we are quite careful to monitor the trajectories and subsequent disposition of the spacecraft, so that we know what has happened to them,” says Dr Conley.
The reason these microbes got out is that it’s not yet possible to completely sterilise a spacecraft before an interplanetary voyage. But all is not lost as Dr Conley explains. “From everything we have seen so far, it’s quite unlikely that any spores carried on those spacecraft have actually landed in a place where they might grow.”
So how exactly do you clean a spacecraft? If you’re now imagining a multi-million dollar probe being lathered in disinfectant by a group of fastidious sponge brandishing scientists, then you’re in for a shock. The reality is much more bizarre. “A variety of cleaning procedures are used, depending on the material requiring cleaning” explains Dr Conley. The aim is to make sure that the number of microbes on the spacecraft does not exceed pre-determined levels. Of all the methods used, the one that has thus far proved most effective is ‘dry heat’ sterilization. Put simply the spacecraft is baked in a giant oven at temperatures of several hundred degrees Celsius, killing most lurking micro-organisms.
Other methods such as swabbing exposed surface panels with alcohol are sometimes used and NASA is also developing other new methods to reduce the amount of potential microbial contaminants. One proposed method involves firing cold plasma at spacecraft, zapping any microbes. Another involves dousing any bacterial stowaways with hydrogen peroxide vapour. “The type of mission and the conditions we find at other planetary bodies are what dictates the level of protection,” explains Dr Conley. Yet, according to Dr Conley, in this article in NASA’s Astrobiology magazine these important protection regulations might generate complications when astronauts want to start exploring worlds like Mars; worlds which might harbour primitive life.
For the most part Mars’ surface is thought to be inhospitable to life, so astronauts will most likely be allowed to roam free over large areas of the barren ochre surface. But what if we actually want them to look at and explore the sites where living microbial life might be found?
That might not be so easy to do warns Dr Conley. “Humans will not be allowed to contaminate locations where Earth life might survive before we have a chance to study them sufficiently for signs of extraterrestrial life,” a proposition that is as reasonable as it is frustrating. If life is present on the red planet then it looks like it will be the electronic eyes of a rover, a wheeled robotic ambassador, which will glimpse the first signs of it. With the future of whole worlds at stake then, scientists can’t risk forgetting to wash their rovers’ wheels.