When I tell people that I spend my days testing the possibility of life on Mars they usually reply in one of two ways. 'No seriously, what do you do?' is only slightly more common than the wittier 'So you're not holding out for much fieldwork, then?' Astrobiology is a bright young discipline, aiming to answer some of the most fascinating questions within science and dinner-table conversation alike. Does life exist 'out there' among the pinpricks of light in the heavens, or are we alone in the cosmos? No current scientific field fires people's fascination more than the quest for extraterrestrial life, and a large proportion of students have cited the reason for continuing science is their interest in astrobiology. For now many astrobiologists' money is on Mars, our planetary neighbour, as it was once a lot like Earth.
The big question, though, is where on Mars are the best places to look for signs of life. We're not talking about green bug-eyed monsters here, but ultra-hardy bacteria-like cells. For the foreseeable future our probes won't drill more than a few meters into the hard-frozen ground. Any bacteria within our robotic reach near the harsh surface would be forced to remain dormant for long periods by the freezing conditions. And I'm looking into just this possibility.
One of the most critical hazards for surface life on Mars is the constant rain of radiation from space. This is composed of sub-atomic particles accelerated to near-lightspeed by solar flares or exploding stars throughout the galaxy. Unlike Earth, Mars isn't shielded by a strong magnetic field or thick atmosphere and these energetic particles slam straight into the surface. Dormant bacteria are unable to repair the cellular damage inflicted by this radiation and it steadily accumulates. The real Martian death rays aren't wielded by tripods, but are the cosmic radiation steadily destroying any life in the soil of the red planet. I've built a computer simulation of the situation, modeling the penetration of cosmic rays through the Martian atmosphere and rock. From this I can calculate the radiation level at any location on Mars, and for different depths beneath the surface. I then use this information to determine from experimental results how long different kinds of bacteria would survive before becoming irrecoverably damaged by the radiation.
There are lots of exciting places on Mars we want to check for life; ancient dry river beds or lakes, or ice in crater bottoms and the polar caps. But which location provides dormant cells the best protection from radiation and how deep will we need to drill? Addressing these questions is vital for any chance of finding survivors, viable cells that could be awoken with a little warming and nutrient. One very promising location that my research has identified is the ‘frozen sea’ near the Martian equator (NewScientist.com 30 January 2007).
Finding irrefutable evidence for extraterrestrial life in the Martian soil would rank among the greatest discoveries of history, with deep ramifications for religion, philosophy and the popular perception of our place in the cosmos. The consequences of such a discovery are played out again and again in the public mind through countless books, films, magazine articles, and at dinner table discussions with friends and family. But it’s also crucial that society starts seriously considering these possibilities now and becomes involved in making the most important decisions. Should humans land on Mars and potentially infect the red planet with earthly germs? Should samples of Martian soil be returned to Earth with the risk of contaminating our biosphere? Why should millions of pounds be spent on a space probe rather than funding pharmaceutical research, for example? If the potential rewards of astrobiological research are so great, so too are the potential risks, and society needs to be involved from the outset to avoid the pitfalls of public distrust, such as encountered by genetic engineering.
My research on the Martian death rays is one piece of the puzzle in the search for life beyond Earth, but your role is just as important. What do you think?