Ten million years ago it was awash with oceans of water. Now it is desert dry. But research published today shows that organic life could still be lurking on Mars.
Scientists will be poring over a slew of papers published by the teams from the US space agency Nasa reporting the results garnered from the two rovers, Spirit and Opportunity, that landed at the beginning of this year and are still exploring opposite sides of the Red Planet.
Even before today's formal publication in the journal Science, many scientists were abuzz over the earliest of the findings, which suggested that water once flowed all over the surface, and is now sequestered beneath it, probably still in liquid form. Furthermore the gas methane, normally associated with biological activity, has been detected in the atmosphere.
"Their findings such as sedimentary rocks [which indicate oceanic activity] are very exciting," said Professor Colin Pillinger, of the Open University, who led the team that developed the European Space Agency's Beagle 2 lander.
"And they are also saying that there's methane in the atmosphere there - which must mean a continuous supply, or it would disappear. My preference is that [methane] is generated through a biological supply - even the reprocessing of already-dead biological material by another living source."
For Professor Pillinger the findings lend extra frustration to the loss of the Beagle 2 lander, last heard of heading towards the Martian atmosphere on Christmas Eve. But he declined to express regret: "We'll get there one day," he said. "I wrote a letter to Nasa three weeks ago suggesting a Beagle 3 lander as a stand-alone element to be included with their 2009 Mars Science Laboratory mission. " He has yet to hear back from the agency.
The work represents the most thorough geological examination ever of a planet other than Earth, offering key insights into how its development resembled and departed from that of our own.
The key surprise, said Dr Karl Mitchell, of the planetary science group at Lancaster University, was the discovery of rock outcrops - which in turn indicated how the planet's surface was eroded. He said: "Most of Mars is covered with a thin veneer of dust, from millions of years of wind erosion. That means you can't see much of what's been going on, geologically speaking."
But seeing an outcrop told scientists what they needed to know: that the rocks were formed by water action, and that huge volumes of water must have flowed over the surface.
"Currently, the surface of Mars is incredibly dry," Dr Mitchell said. "But we think there's water in the poles, as ice, and underground. It must have been driven to the surface by volcanic activity until relatively recently - about 10 million years ago. That's only 1 per cent of Mars's lifetime, because it is 4.5 billion years old. If it could happen then, it could happen again."
The deep-lying water had to be liquid, because it would be impossible for a volcano to melt enough ice quickly enough to flood the areas shown to have been affected. "It would require about one million cubic metres per second, which would be devastating on Earth," Dr Mitchell said.
The plethora of findings has deepened understanding of Mars, and justified the $820m (£510m) cost of the landers - which are still working, having long outlasted their planned mission of 90 Martian days, 92 Earth days. Funding to run the landers runs out at the end of September.
However, Dr Mitchell said it was still important eventually to send humans to investigate the planet. "A geologist can notice things and react in a way a machine can't," he said. "But right now you can't get humans out there, and robots are becoming extremely impressive - what these ones did wouldn't have been possible a few years ago."
Professor Pillinger cautioned: "I don't think it would be responsible to send people until we're sure that there's life there. And we should be very careful about bringing it back."Reuse content