Some time earlier this month, Nasa's Phoenix Lander slipped into a cold-induced coma in the Arctic wastes of the Red Planet. With the onset of winter, the Sun dropped low in the sky, and the temperature fell to -130ºC at night.
Despite being wrapped up as warmly as Nasa's scientists could manage, the lander's electronics – particularly its batteries – were vulnerable to the cold. Without the power from its solar panels, there is little hope that Phoenix will rise again from its long hibernation.
The end of Phoenix's mission illustrates the difficulty we scientists face in probing the secrets of the Red Planet – and in particular in answering the biggest question of all: "Is there, or was there, life on Mars?" The world's media have been maintaining that we are about to find out the answer since the end of the 19th century, when Percival Lowell claimed he could see canals there. QED – there had to be intelligent Martians, and they would be 15ft tall and live in oases.
In the case of Phoenix, the intention was never to search for life, but it would have been nice to know whether the ice cap of Mars was a good place to send appropriately equipped landers for follow-up missions.
Unfortunately, Nasa's latest project didn't complete one of the experiments in which the life-seekers were particularly interested: pyrolysing (heating up) soil samples to separate out any organic matter. It did carry a suitable instrument – a high-tech oven-cum-mass-spectrometer called the TEGA – but it proved too difficult to get frozen clods of soil inside, and only one of the eight tests produced the sort of data the investigators were hoping for.
Technologically speaking, of course, the latest mission was a success as soon as it touched down: it proved that Nasa still knows how to land on its feet. The lander was called "Phoenix" because it was Nasa's second attempt to explore the poles after the failure of the Mars Polar Lander in 1999, when the computer shut down the descent engine while the robot was still some way above the surface.
In the interim, there had been two successful landings, of the Exploration Rovers Spirit and Opportunity, but they had used gas-filled bags to break their fall and bounce to rest. The success of Phoenix's downward-pointing cameras, and hazard-avoidance navigation systems, mean that the space agency can be much more choosy in future when selecting its targets.
Phoenix also accomplished much once on the surface. It lasted longer than its creators had anticipated, sending back pictures of a different kind of terrain and – after looking skywards – recognising that it was snowing. The robotic arm dug deep trenches through an ice layer, managing to melt some. The MECA experiment measured the pH (the acidic/alkalinity) of Mars's soil, and showed it to be slightly alkaline rather than very acidic, as some had predicted. It also identified a number of the ions responsible.
But none of these findings really contributes to that vital argument as to whether life can exist on Mars. On Earth, we know that there are microorganisms, called extremophiles, which can do their thing at almost any pH, in very salty or fresh water, at temperatures over 1,200C near the vents of volcanoes, or in the freezing cold of Antarctica. They even exist in atomic reactors. It would have been so much better to have seen some results that suggested there were a few bodies around on Mars – even dead ones.
This was the problem encountered in 1976 by Nasa's first life-detection laboratories, aboard the Viking landers. The Vikings had ways of releasing nutrients that might have been gobbled up by ravenous mini-Martians and turned into recognisable metabolic waste products.
These experiments seemed to work – but, because no accompanying organic matter could be found, the scientists decided that a chemical, rather than a biological, effect was being observed. As one famous planetologist, Carl Sagan, observed: "If you want to prove something extraordinary, you have to have extraordinary proof." But as Martin Rees, the future president of the Royal Society, said at the time: "The absence of evidence isn't evidence of absence", so the search continued.
In 2003, my own Beagle 2 team also thought we might be able to answer the vexed question of life on Mars. Our lander carried the experiment used on Earth to demonstrate that all sedimentary rocks (ie those deposited in water) contain carbonate minerals and organic matter from micro-organisms.
These are the chemical data, as opposed to fossil records, which can be disputed, that suggest life on Earth started nearly four billion years ago.
Results obtained from meteorites blasted off Mars long ago, and serendipitously delivered to Earth, seemed to show that there had been life on the Red Planet as recently as 700,000 years ago, at a time when hominids, the precursors of modern humans, were walking around on our own planet.
There is circumstantial evidence that the organic materials found are genuinely Martian, rather than being the result of contamination on Earth – but circumstantial evidence isn't proof positive.
To eliminate the spectre of contamination, Beagle 2 was going to perform the same experiments on Mars. Unfortunately, the mission was a failure, even though the money wasn't wasted: the Wellcome Trust is exploring using the skills acquired in the early detection of TB.
But now that Phoenix seems to have frozen stiff, where do we go from here? Nasa's landers from 2004 are still happily chugging around near the Equator. But its next landing mission, which involves lowering a car-sized rover on a "sky crane", needs more than $2 billion to complete. It is scheduled for launch in 2009, but with a new administration with new priorities, it could be delayed, or worse.
The European Space Agency has been threatening to go back to Mars with a lander ever since Beagle 2 declined to call home. At first it was in 2009, then it shifted to 2011, then 2013. The plan now is to launch in 2016 and arrive in 2017, maybe. At the same time, European science ministers will be asked this week to double the budget from €600 million to 1.2 billion, or to fund a cut-down version at 1 billion. In the current economic climate, this is far from a foregone conclusion.
In other words, a Mars sample return that might provide a definitive answer to the question of extraterrestrial life is – as always – at least 15 years away. As for putting humans on Mars, that's pretty much a joke.
Of course, I'm sure there are plenty of people worrying about mortgages to pay and families to feed who are entirely unconcerned about whether there is life on Mars. But if we could show that life exists, or had existed on just one other planet, we could extrapolate to a universe teeming with life.
Studying another form of life would help us understand how life started, just as Darwin recognised how it developed via evolution by seeing how different life forms changed in the different places he visited. This would be the ultimate solution to another of our existential conundrums: "Where do I come from?"
And me? Ideally, I'd like a Beagle 3 or Beagle 4 – the technology isn't obsolete, and seems a snip now at £40 million. But if not, I'll do what the Brits always do when our team doesn't qualify: watch anyway, and cheer for the underdogs of the space exploration scene – Japan, China and India – who don't seem to be frozen by fear of failure.
Colin Pillinger is Professor of Planetary Sciences at the Open University, and led the team behind the British lander Beagle 2
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