The existence of extra-terrestrial life might just be the most far reaching question that science (and yes, even geology) can ask. It goes to the heart of ideas which seem to border on the philosophical: big concepts like our place in the universe – and even the origins of life itself.
And, few would argue, our best chance of an answer currently lies on a small, barren world at the edge of the asteroid belt; when you think of Mars, after all, the words “life” and “on” are rarely far behind. But impressive as they are, our forays onto its rusty surface have not turned up the one discovery we all crave. The Red Planet, it seems, might also be rather … well it rhymes with red.
But as Mars begins to give up its geological secrets, the search for life is taking an intriguing new turn. It seems that, deep down, our solar neighbour could be hiding a different, much more Earth-like side.
In Deep Water?
When your probe is finally looking down onto its alien target – amazingly, somehow, the surface of another planet – the seemingly mind boggling task of looking for life in fact boils down to a single goal: the search for liquid water. When it comes to Mars, this search has traditionally been focused above ground – on the rocky landscape, with its suggestive channel formations. Recently, though, a rare glimpse beneath the dust could be about to bring the hunt for Martian microbes into a surprising new arena.
One of the most important discoveries to have come from Mars in the last few years, was the discovery, in 2009, that rocks within impact craters, brought up from thousands of meters below the surface, contained traces of hydrothermal minerals ; that is, these deep rocks had once been in contact with hot water.
On Earth, water-filled pores within the crust provide an ideal habitat for countless varieties of microorganism – in fact, almost half of life “on” our planet actually occurs below the surface, sustained not by the sun, but deep geothermal heat. In light of this, it soon became clear that the possibility that similar conditions might have existed on Mars had extremely exciting implications in the search for life: while the surface may have been hostile for billions of years, an underground reservoir – warmed by the planet’s core, and sheltered from the violence of the early solar system – could potentially have provided a safe haven for life to flourish.
The big question, of course, is how to find out; surely all traces of organic matter in the crater rocks would have been destroyed by any collision powerful enough to rip them from the crust! Excitingly, though, it is now emerging that the deep, potentially life-bearing fluids in Mars’ interior could have reached the surface in another way – and might, therefore, be within our reach. New research, published last month in the journal Nature Geoscience , has identified an area of the Martian surface which could, quite simply, be hiding the greatest discovery of all time…
All eyes are now on McLaughlin crater: a huge, two-kilometer dent in Mars’ northern hemisphere. Among the thousands of similar craters which dot Mars’ surface, McLaughlin is unique: as well as being exceptionally deep, it also occurs at a topographic low, making it in effect a natural borehole into the crust. The authors of the study argue that if the deep, hot fluids ever made it to the surface, it would probably have been here.
And thrillingly, their work has revealed not only signs of water but, astonishingly, that an entire lake existed within the crater floor. Furthermore, the discovery of rare clays and carbonate minerals suggest that this water had a particularly deep source. And which, taken together – the authors conclude – suggests that deep hydrothermal fluids did indeed reach the surface, leaking out into McLaughlin crater and feeding its lake.
And also, perhaps, leaving signs of life? With the potential for a “vast microbial biosphere” , Mars’ deep water might be about to become our next great hope – and McLaughlin crater, quite possibly, our next target.
1. Ehlmann, B. L. et al. Identification of hydrated silicate minerals on Mars using MRO-CRISM: Geologic context near Nili Fossae and implications for aqueous alteration. J. Geophys. Res.114, E00D08 (2009).
2. Michalski, J.R. et al. Groundwater activity on Mars and implications for a deep biosphere. Nature Geoscience 6 (2013).