Mineral formations cited as remnants of a living organism on a martian meteorite may have been forged at temperatures too hot for known life-forms, according to an analysis presented today at the American Astronomical Society's Division for Planetary Sciences meeting in Tucson, Arizona. The finding, if substantiated, would weaken the case for martian life.
Kevin Hutchins and Bruce Jakowsky, planetary scientists at the University of Colorado, Boulder, claim that the NASA team whose original work appeared in Science failed to account for the evolution of the martian atmosphere in calculating the temperature at which carbonate globules in the meteorite formed. Earthly bacteria cause similar formations of carbonate globules.
Hutchins says data from the Viking spacecraft that landed on Mars in 1976 indicate that the planet's atmosphere has a higher ratio than Earth's atmosphere of some heavy isotopes, such as oxygen-18. Scientists use isotopic ratios to calculate the temperature at which carbonates form. When Hutchins and Jakowsky used the isotope ratios from their model of the martian atmosphere, they calculated that the lower limit of carbonate formation from carbon dioxide on Mars is between 40 degrees and 250 degrees Celsius, significantly higher than the original calculations of 0 to 80 degrees C. Scientists don't believe life on Earth exists at temperatures higher than 150 degrees C.
Hutchins points out that the Science paper did present two conflicting views on the temperature of carbonate formation, one which suggested a temperature as high as 700 degrees C. The paper's authors, however, said the lower temperature was more likely.
Don't count martian life out yet, however. The new temperature range is still wide enough to allow for carbonate formation associated with an organism, says Michael Meyer, NASA's exobiology program manager. Hutchins agrees: ``What we're saying is that the uncertainty for life [on this meteorite] is going up.''