Frozen Mars bars possibility of life

Or does it?

By Lucy Sherriff, 22nd July 2005

A chemical analysis of Martian meteorites has revealed that the red planet was probably freezing cold for the vast majority of its existence, casting doubt on theories that life could have had time to evolve on the planet.

Researchers from the California Institute of Technology (CIT) and the Berkeley Geochronology Center (BGC) said that the level of Argon present in the rocks could be used to deduce what kind of environment the meteorites had been exposed to. They concluded that the samples they examined could have been at temperatures above freezing for no more than a million years in the last 3.5bn years of history.

The research, to be published in the journal Science, is likely to provoke lively debate because, at first sight, the findings appear to contradict visual evidence that water flowed on the surface of the planet. The vast canyons, river beds and many other erosional features have been widely interpreted to mean that liquid water flowed on Mars for many years, possibly long enough for life to establish a foothold.

The authors of this new research say that if there was liquid water on the surface of Mars, it was only there for relatively short periods.

"Our research doesn't mean that there weren't pockets of isolated water in geothermal springs for long periods of time, but suggests instead that there haven't been large areas of free-standing water for four billion years," David Shuster of the California Institute of Technology told the BBC.

He and Benjamin Weiss of the Berkeley Geochronology Center examined two of the so-called nakhlite meteorites, and the famous ALH84001 meteorite, which made headlines when researchers though they had uncovered fossilised bacteria in the rock. They conducted two sets of tests: one to check for evidence of heating, and the other to develop a profile of the environment the rocks existed in before being ejected from Mars.

In the second test, the researchers estimated the amount of Argon present in the samples. Argon, a noble gas, is present in some rocks on Earth, and in meteorites, as a result of isotopes of potassium decaying. The gas escapes from the rocks at different rates, depending on the temperature, so the researchers can use it to put upper and lower limits on the kind of environment the rocks experienced.

In related news, NASA said yesterday that the launch window for its next mission to Mars will open on 10 August. The Mars Reconnaissance Orbiter will examine the planet from a low orbit, and should provide what NASA describes as "unprecedented detail", possibly more data "than all previous missions combined". ®