Among planetary scientists, the tide is turning, says Mark Peplow.
Life found on Mars. It's a story that would forever change our notions about the Universe, and our own place in it. And while we have no firm evidence for life away from our planet, many scientists are now increasingly happy to admit that they do believe there is life on the red planet.
An informal poll of 250 scientists attending the Mars Express Science Conference at Noordwijk in the Netherlands last month revealed how high their hopes have climbed. About three-quarters think life could have existed on Mars in the past, and a quarter think life could be there today.
“Ten years ago, a firm belief in life on Mars would have marked you out as a crank. ”
Everett Gibson, the geochemist from NASA's Johnson Space Centre in Houston, Texas, who conducted the poll, says that this 'life' would most likely be bacterial.
Ten years ago, a firm belief in life on Mars would have marked you out as a crank, or at least a hopeless optimist. But now, leading scientists regularly speak about finding life on Mars as virtually inevitable, with barely a caveat to remind us that we currently have no proof at all.
Surely scientists are meant to be rational beings, believing only what they can prove? Wrong. Science is a creative human endeavour, and as such it is shaped by our hopes, dreams and fears, just like literature, archery and plumbing.
Still, scientists in other fields are notoriously reluctant to be drawn on what they believe, rather than what they know. So what has changed in planetary science that has emboldened its practitioners to speak from the heart, rather than the head?
For starters, our understanding of martian history is better than ever before. In the past year we have discovered frozen seas, gases that supposedly hint at life, and geological evidence for salty seas and periodic floods on Mars in the past.
“Science is a creative, human endeavour. It is shaped by our hopes, dreams and fears, just like literature, archery or plumbing. ”
As the discoveries just keep on coming at an ever-accelerating pace, it seems more reasonable than ever to extrapolate and discuss the chances of life on the red planet.
In particular, whiffs of methane and formaldehyde (see 'Formaldehyde claim inflames martian debate') fit with the idea of subsurface methanogenic bacteria, and discoveries of extremophile bugs back home on Earth show us just how resilient life can be.
If bugs can survive in utter darkness, without oxygen, inside hydrothermal vents, then surely something could carve itself a niche on Mars? As Ian Malcolm, Jeff Goldblum's character in the film Jurassic Park, puts it: "I'm simply saying that life finds a way."
Then there are the swelling ranks of people actively looking for life. Many more scientists than ever before work in astrobiology, and I'd bet that most of them believe that we will one day find life 'out there' - after all, why would anyone pursue what they thought was a futile field of research?
"Today, it seems nearly everyone is an astrobiologist," wrote Jeffrey Bada, an astrobiologist at the University of California, San Diego in La Jolla, in a recent book review in Science magazine1. "A decade ago, I knew essentially none."
NASA's astrobiology programme began in the early 1960s, and thirty years later Ames Research Centre at Moffett Field, California, was officially designated as a centre for astrobiology.
Then, in 1996, scientists announced that a martian meteorite found in Antarctica carried evidence of life. The rock, called ALH84001, contained hydrocarbons and minerals associated with biological processes, along with tiny globules of carbonate minerals interpreted as bacterial microfossils2. However, most experts remain unconvinced by this interpretation.
But Bada argues that the ALH84001 controversy gave the field a huge boost, and enthusiastic scientists began to justify research proposals with tantalizing hints that their experiment could be the one to discover our planetary neighbours.
Scientists pitching for an instrument to analyse Mars' atmospheric chemistry could now add that their results may give clues about life.
“Scientists willing to stick their neck out over life on Mars are more likely to be handed a cheque than lose the respect of their colleagues. ”
With more money available from a publicity-conscious space agency, and more researchers claiming to look for life, optimism has been on the rise ever since. While meteoriticists may have been made more cautious by the ALH84001 controversy, there has been an influx of geologists and chemists with no qualms about tackling the bug hunt from a new perspective.
But although the fresh blood may be good for optimism, it's not necessarily good for hard evidence. Rocco Mancinelli, an astrobiologist at NASA's Ames Research Center in Moffett Field, is extremely sceptical about the latest claims linking martian gases with life, for example.
"This is what happens when non-microbial ecologists speculate on microbial ecology," he says.
There are also increasing opportunities to find life in situ. Roving robot laboratories designed to look for life are being planned for launch by the end of the decade, and a space mission to return rock samples from Mars is almost certain to happen within the next 15 years.
So now is the time to place your bets. With NASA's renewed emphasis on human exploration of our Solar System, scientists willing to stick their neck out over life on Mars are more likely to be handed a cheque than to lose the respect of their colleagues.
When put on the spot, almost all of these scientists agree that there is not enough evidence for life yet. But scientists, like all of us, need something to believe in, says Yuk Yung, a planetary geologist from the California Institute of Technology in Pasadena.
Although doubtful about recent evidence hinting at life, he cheerfully admits: "I do believe in life on Mars." The problems arise when that belief begins to shape their interpretations of the data, he adds, which is why this field will undoubtedly see many more controversies yet.
Despite these claims and counter-claims, we will never lose our appetite for this quest because it is so fundamental to our own origins. And as long as a belief in life on Mars continues to drive research efforts, let the speculation continue, say I.
In that spirit, it would of course be disingenuous of me to duck the question myself. So here goes: I believe that one day we will find firm evidence of life on Mars.
There, I've said it. So what about you?
Send your thoughts to firstname.lastname@example.org.
BadaJ. L. Science 307, 46 (2005).
McKayD. S. et al. Science 272, 924 (1996).