Health & Science

Lakes and rivers on ancient Mars; How menthol helps hook smokers; Why Africans are susceptible to HIV; More painful than a melting iceberg

Lakes and rivers on ancient Mars

Mars was once a warm and wet planet, with vast lakes, flowing rivers, broad deltas—and, possibly, some form of life. Photos and data from the Mars Reconnaissance Orbiter, now circling the Red Planet, found widespread deposits of mineral-laden clay throughout Mars’ southern hemisphere, from valleys to dunes to the tips of volcanoes. This, say planetary geologists in a new study in Nature, indicates that the entire area was under water early in the planet’s history, about 4 billion years ago. The planet apparently remained wet for about 800,000 years, and was also much warmer than it is today, with surface temperatures of 200 degrees or more. “What does this mean for habitability? It’s very strong,” says planetary geologist Jack Mustard of Brown University. “It was a benign, water-rich environment for a long period of time.” Today’s Mars is a frozen wasteland, with daily temperatures of around minus-60 degrees Fahrenheit. Any water that remains exists as permafrost or is buried far below the surface of the planet, and NASA’s Phoenix Mars Lander is now digging in that permafrost in an attempt to find proof of both water and organic molecules. Scientists are now eager to launch a more ambitious mission to collect direct evidence of Mars’ warm, wet past, and to search for clues that microbes or plants once thrived there. “It’s clear that we need to work together to figure out a way to go to Mars, collect a sample of these rocks, and bring them back to Earth,” astrophysicist Joe Michalski tells National Geographic News. “That’s really going to be the next milestone.”

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