Mössbauer Group identifies carbonate mineral formation in the Columbia Hills consistent with the reported findings for meteorite ALH 84001
Some four billion years ago, our neighbor planet Mars had a warm and wet climate and would thus have provided a much more favorable environment for the development of life than today. This is the conclusion following a recent study undertaken with several instruments on one of NASA's Mars Exploration Rovers (MER), Spirit. The main body of evidence was provided by the 2006 survey results obtained by NASA's rover Spirit in the Columbia Hills region of Mars using the Mössbauer spectrometer developed in Mainz.
"Working in collaboration with an international group, the Mössbauer team has now for the first time been able to demonstrate the presence of deposits of carbonate minerals in situ on the Martian surface. This is the kind of proof that we have long been looking for to support the hypothesis advanced some decades ago that the planet once had a warm and wet climate," explains Dr. Göstar Klingelhöfer of Johannes Gutenberg University Mainz. The results of the study have now been published in the journal Science.
During the project, the researchers worked on the assumption that, in order to have had a warmer and wetter climate during its early history, Mars would have to have had a much denser atmosphere with considerably higher levels of CO2 than today. This sort of atmosphere would result in the formation of rocks with high carbonate mineral content. Analyses conducted over a period of several years have enabled the Mössbauer Group to identify a rocky outcrop of just this kind on Mars that contains significant amounts of magnesium iron carbonate. "Although we were already aware that the data obtained from Columbia Hills was inconsistent with standard theories, we did not quite know how to interpret it," Klingelhöfer continues. His team developed the miniaturized Mössbauer spectrometer that is attached to the rover and is designed to analyze iron-containing minerals on the surface of Mars.
Over the past several years, NASA scientist Richard Morris has been analyzing the results in a series of laboratory experiments. Findings reported by two other rover instruments – the alpha particle X-ray spectrometer developed by the Max Planck Institute for Chemistry in Mainz and a thermal emission spectrometer – corroborate the evidence: The rocky outcrop dubbed 'Comanche' consists of nearly 20 percent carbonates. Rocks with such a high content of carbonates can only have formed in the presence of large volumes of water with a more or less neutral pH in a dense, warm, moist CO2-rich atmosphere – conditions that would be ideal for life.
"This carbonate is exactly what we have always been looking for," claims a happy Göstar Klingelhöfer in view of the findings, which demonstrate the presence of mainly magnesium iron carbonate and the silicate mineral olivine in the rocks. And Steve Squyres of Cornell University in Ithaca, New York, is equally enthusiastic: "This is one of the most significant findings by the rovers." Squyres is Principal Investigator of the Mars Exploration Rover Mission and co-author of the recent Science article.
Incidentally, this composition is similar to that reported for the carbonate globules present in Mars meteorite ALH 84001discovered in the Allan Hills in Antarctica. In the late 1990s, the Allan Hills meteorite made headline news worldwide when researchers claimed that certain structures within it may represent biological signatures. Like the Comanche outcrop in the Columbia Hills in the Martian Gusev crater, ALH 84001 is estimated to be some 4 billion years old. The scientists postulate that the Gusev rocks, with their significant 16 to 34 percent content of carbonates, were probably deposited from a carbonate-rich solution with a near neutral pH under hydrothermal conditions – similar to those obtained in the hot springs on Iceland and Spitzbergen – during a period of volcanic activity in the so-called Noachian epoch some 3.5 to 4.6 billion years ago.