US probes may have found life on Mars 30 years ago: researchers

WASHINGTON - NASA's Viking Mars probes may have found living organisms when they landed on Mars 30 years ago, but possibly destroyed them by exposing them to water, according to two astrobiologists.

"I think the Viking results have been a little bit neglected in the last 10 years or more," Dirk Schulze-Makuch told the American Astronomical Society meeting from the weekend through Wednesday in Seattle, Washington state.

"But actually, we got a lot of data there and recent findings about Earth organisms that live in extreme environments, and improvements in our understanding of conditions on Mars, give astrobiologists new ways of looking at the 30-year-old data," from the probes, he added.

The scientist and his colleague Joop Houtkooper of Justus-Liebig-University, Giessen, Germany, have published their findings on the website of Washington State University, where Schulze-Makuch teaches.

The researchers hypothesize that Mars is home to microbe-like organisms that use a mixture of water and hydrogen peroxide (H2O2) as their internal fluid.

Such a mixture would provide at least three clear benefits to organisms in the cold and dry Martian environment, said Schulze-Makuch.

Its freezing point is as low as minus 56.5 degrees Celsius, depending on the concentration of H2O2; and H2O2 is hygroscopic, which means it attracts water vapor from the atmosphere, a valuable trait on a planet where liquid water is rare, the scientist added.

On Earth, some microbes in the soil tolerate elevated concentrations of H2O2 in their surroundings, and the species Acetobacter peroxidans use hydrogen peroxide in its metabolism.

Scientists working on the Viking project in the 1970s were not looking for organisms that rely on H2O2, because at the time nobody was aware that such organisms could exist.

Research of "extremphiles," organisms capable of adapting to extreme environments such as volcanic fumaroles at the ocean bottom, did not take off until the 1990s.

Schulze-Makuch and Houtkooper also explained how the experiments carried aboard the two Viking probes may have inadvertedly killed any living organisms Martian soil may have contained.

They said the soil samples collected on the Red Planet were exposed to water which would be make microbes using a water-hydrogen peroxide mixture "either drown or burst" due to water absorption.

They said the National Aeronautics and Space Administration's Phoenix mission to Mars scheduled to launch in August 2007 offers a good chance to further explore their hypothesis.

Agence France-Presse