PASADENA, Calif., July 22 (UPI) -- California researchers say their study of the chemical makeup of Martian meteorites suggests the planet has always been cold and rarely above freezing.
David Shuster of the California Institute of Technology, and Benjamin Weiss, of the Berkeley Geochronology Center, analyzed two of the seven known "nakhlite" meteorites -- the El Nakhla meteorite and the ALH84001 meteorite that some scientists believe show evidence of past microbial activity on Mars.
The researchers, in a study published in Science, reconstructed a "thermal history" for the meteorites to estimate the maximum long-term average temperatures they were subjected to, the BBC reported Friday.
Shuster says ALH84001 could never have been heated to more than 350 degrees Celsius for even a brief period of time during the last 15 million years.
The erosional features believed to be caused by water on Mars must have been made during very brief periods, Shuster says.