US:Two Nasa space probes that visited Mars 30 years ago may have stumbled upon alien microbes on the Red Planet and inadvertently killed them, a scientist has claimed.
The problem was the Viking space probes of 1976-77 were looking for the wrong kind of life and did not recognise it, the researcher said in a paper presented yesterday at a meeting of the American Astronomical Society in Seattle.
The new report, based on a more expansive view of where life can take root, may have Nasa looking for a different type of Martian life form when its next Mars spacecraft is launched later this year, one of the space agency's top scientists said.
Last month, scientists excitedly reported that new photographs of Mars showed geological changes that suggest water occasionally flows there - the most tantalising sign that Mars is hospitable to life.
In the 1970s, the Viking mission found no signs of life. But it was looking for Earth-like life, in which salt water is the internal liquid of living cells.
Given the cold dry conditions of Mars, that life could have evolved on Mars with the key internal fluid consisting of a mix of water and hydrogen peroxide, said Dirk Schulze-Mach, author of the new research.
That's because a water-hydrogen peroxide mix stays liquid at very low temperatures (-55.56 degrees), does not destroy cells when it freezes, and can suck scarce water vapour out of the air.
The Viking experiments of the 1970s would not have noticed alien hydrogen peroxide-based life and, in fact, would have killed it by drowning and overheating the microbes, said Mr Schulze-Makuch, a geology professor at Washington State University.
One Viking experiment seeking life on Mars poured water on soil. That would have essentially drowned hydrogen peroxide-based life, Mr Schulze-Makuch said. A different experiment heated the soil to see if something would happen, but that would have baked Martian microbes, he said.
"The problem was that they didn't have any clue about the environment on Mars at that time," Mr Schulze-Makuch said.
"This kind of adaptation makes sense from a biochemical viewpoint." Even earth has something somewhat related. He pointed to an earth bug called the bombardier beetle that produces a boiling-hot spray that is 25 per cent hydrogen peroxide as a defence weapon.
Mr Schulze-Makuch acknowledges he cannot prove that Martian microbes exist, but given the Martian environment and how evolution works, "it makes sense".
In recent years, scientists have found life on earth in conditions that were once thought too harsh, such as an ultra-acidic river in Spain and ice-covered lakes in Antarctica.
Mr Schulze-Makuch's research coincides with work being completed by a US National Research Council panel nicknamed the "weird life" committee, which worries scientists may be too earth-centric when looking for extra-terrestrial life.
The problem for scientists is that "you only find what you're looking for," said Penn State University geosciences professor Katherine Freeman, a reviewer of the NRC work.
A new Nasa Mars mission called Phoenix is set for launch this summer, and one of the scientists involved said he was eager to test the new theory about life on Mars.
However, scientists must come up with a way to do that using the mission's existing scientific instruments, said Nasa astrobiologist and Phoenix co-investigator Chris McKay. He said the Washington State scientist's paper piqued his interest. - (AP)