EARLY NASA probes visiting Mars 30 years ago may have stumbled upon life on the Red Planet - and inadvertently destroyed it.
The two Viking spacecraft of 1976-7 were looking for the wrong kind of life and would not have recognised the kind of alien microbes they might have found, delegates attending the American Astronomical Society in Seattle have been told.
The race
to find extra- terrestrial life on Mars is one of the most exciting challenges facing scientists, with the NASA Phoenix Mars mission leaving in the summer and the Aurora European project developing technology to land on the planet.
The report, based on a more expansive view of where life can take root, could see Phoenix looking for a different type of Martian life form.
Last month, photographs of Mars showed geological changes suggesting water occasionally flowed there - the most tantalising sign Mars is hospitable to life.
In the 1970s, the Viking mission found no signs of life. But Professor Dirk Schulze-Makuch, author of the latest research, said it was looking for Earth-like life, in which salt water is the internal liquid of living cells.
Given the cold, dry conditions on Mars, life could have evolved with the key internal fluid a mix of water and hydrogen peroxide.
Prof Schulze-Makuch, of Washington State University's department of geology, said one Viking experiment poured water on soil, which would have drowned hydrogen peroxide-based life.
Another experiment, which involved heating soil, would have baked Martian microbes.
Prof Schulze-Makuch acknowledges he cannot prove Martian microbes exist, but, he said, "it makes sense".
Dr John Davies, project scientist at the Royal Observatory in Edinburgh, said: "Prof Schulze-Makuch's statement is perfectly reasonable considering the assumptions made at the time and the fact there was always some ambiguity about the test results.
"There is no evidence on the surface for life such as animals, fish or grass, but the belief now is that any kind of terrestrial life could be microbes living a few inches under the soil to avoid ultra violet radiation."
Professor John Brown, the Astronomer Royal for Scotland, said: "There is general concern over machines landing in space and contaminating the environment. We should not just assume we are not killing things.
"We need to be more careful about what we are doing."
Prof Schulze-Makuch's research coincides with work being completed by a National Research Council (NRC) panel nicknamed the "weird life" committee. The group is concerned that scientists looking for extraterrestrial life may be too Earth-centric.
The problem for scientists searching for life is that "you only find what you're looking for", said Professor Katherine Freeman, of Penn State University's geosciences department and a reviewer of the NRC work.
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www.thespaceplace.com50 YEARS OF SEARCHING
IN THE 1950s, it was believed there could be life on Mars.
Six missions to Mars by the USSR and US in the early 1960s failed.
After Mariner 4, the US mission, sent images back in 1967 of a cratered surface, it was assumed Mars was barren.
In 1971, that changed after Mariner 9, the US's Mars orbiter, sent hi-resolution images showing river and channel-like features.
In 1976, two US missions, Viking 1 and 2, found no life.
In 2003, robots from the US Mars Exploration Rover Mission showed water had existed on Mars.
This summer, Phoenix will study the surface of Mars' high-northern latitudes.
And in 2009, a mobile scientific laboratory will land on a site chosen for its life-sustaining capacity.
