Two Mars space probes, named Spirit and Opportunity, are rocketing toward Mars with an expected arrival time next January.

Spirit was launched June 10, Opportunity, July 7. They are to land on opposite sides of Mars.

Each probe is carrying an all-terrain robotic exploration vehicle called a rover, laden with tools, instruments and electronic gear destined to provide a clearer-than-ever portrait of the red planet's surface.

NASA'S Jet Propulsion Laboratory in Pasadena, California, has been performing routine in-flight tests on the instruments aboard both probes, and has detected in one a possible malfunction.

"The Mossbauer spectrometer on Spirit is the one whose test data did not fit the pattern expected from normal operation," said a NASA statement.

"The Mossbauer spectrometers give information about the arrangement of iron atoms in the crystalline mineral structure within a rock." it said.

But there is hope it can be fixed.

"The Mossbauer spectrometer on Spirit is working, and even if we don't come up with a way to improve its performance, we'll be able to get scientific information out of the data it sends us from Mars," said Steve Squyres.

Squyres, a Cornell University professor and principal investigator for the science tools on each rover, said the spectrometer "is a very flexible instrument, with lots of parameters we can change.

"We have high hopes that over the coming months we'll be able to understand exactly what's happened to it and make adjustments that will improve its performance," he said.

"And if the Mossbauer spectrometer on Opportunity behaves on Mars the way it did today, we'll get beautiful data from that instrument."

The spectrometers, build by Germany's Johann Gutenberg University, is designed to identify the presence of ferrous minerals in any rock or soil against which it is placed. That data will determine the role of water in the formation of the minerals and give a clue to Mars' past climate, NASA said.

SPACE.WIRE