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Researchers at the California Institute of Technology (Caltech) have directly determined the surface temperature of early Mars for the first time, providing evidence that's consistent with a warmer and wetter Martian past.

By analyzing carbonate minerals in a four-billion-year-old meteorite that originated near the surface of Mars, the scientists determined that the minerals formed at about 18 degrees Celsius (64 degrees Fahrenheit). "The thing that's really cool is that 18 degrees is not particularly cold nor particularly hot," says Woody Fischer, assistant professor of geobiology and coauthor of the paper, published online in the Proceedings of the National Academy of Sciences (PNAS) on October 3. "It's kind of a remarkable result."

Knowing the temperature of Mars is crucial to understanding the planet's history—its past climate and whether it once had liquid water. The Mars rovers and orbiting spacecraft have found ancient deltas, rivers, lakebeds, and mineral deposits, suggesting that water did indeed flow. Because Mars now has an average temperature of -63 degrees Celsius, the existence of liquid water in the past means that the climate was much warmer then. But what's been lacking is data that directly points to such a history. "There are all these ideas that have been developed about a warmer, wetter early Mars," Fischer says. "But there's precious little data that actually bears on it." That is, until now.
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