Was Mars too cold to sustain life?

Researchers from the two universities conducted a study on meteorites found on Earth that were originally from the surface of Mars. They concluded that the rocks likely remained at the freezing point or lower for 4 billion years while on the Red Planet. The meteorites studied were ejected from Mars 11 million to 15 million years ago.

If the surface of Mars was freezing during that 4 billion-year period, free-standing bodies of water would likely have been somewhat rare and short-lived. If water existed, it would have been locked up as ice. As a result, the formation and evolution of life forms would have been exceedingly difficult.

The only time Mars may have had an environment hospitable to the formation of life may have been in the first half-billion years of its existence, according to MIT assistant professor Benjamin Weiss and David Shuster, a CalTech grad student.

The study involved reconstructing a thermal history of two of the seven known "nakhlite" meteorites (named after El Nakhla, Egypt, where the first such meteorite was discovered) and a meteor known as ALH84001, which some scientists believe shows evidence of microbial activity.

The researchers first tried to estimate the maximum temperature the meteorites were exposed to. They concluded that ALH84001 could never have been heated to a temperature higher than 650 degrees Fahrenheit during the last 15 million years. The nakhlites, which show very little evidence of shock damage, were unlikely to have been above the boiling point of water during ejection 11 million years ago.

Second, the two tried to estimate the long-term maximum average temperature, by examining how quickly argon gas has leaked out of the rocks. Argon leakage is controlled by the outside temperature. The nakhlites have been in a deep freeze for 4 billion years. By contrast, ALH84001 could only have been above freezing for more than a million years during the last 3.5 billion years.

"The small amount of argon loss that has apparently taken place in these meteorites is remarkable. Any way we look at it, these rocks have been cold for a very long time," Shuster said in a statement. "The temperature histories of these two planets are truly different. On Earth, you couldn't find a single rock that has been below even room temperature for that long."

Still, the study did not rule out the possibility of "panspermia," a theory that states that microbes can jump from one planet to another by meteorites. If microbes were somehow present on ALH84001, they could have made it to Earth when the meteorite landed. The nakhlites have never been heated above about 200 degrees Fahrenheit, which means that any microbes on them (assuming they existed) were not heat-sterilized on the way to Earth.