Magnetic Lava Legacy on Mars?

Mars Global Surveyor, the NASA probe that went into orbit around the Red Planet 12 September, has detected magnetic anomalies dotting Mars's crust, scientists announced today at a press conference held at the Jet Propulsion Laboratory in Pasadena, California. Each of these regions has a magnetic orientation that differs from the weak field that the spacecraft detected when it first arrived (ScienceNOW, 17 September). The anomalies could help researchers understand how the global field behaved--if it ever existed--and what made it disappear.

So far, the Global Surveyor has spotted magnetic anomalies on eight of its 11 passes over Mars. From a height of 120 kilometers, the anomalies have a strength of about 400 nanoteslas--about 40 times stronger than any such anomalies on Earth. "Nobody expected an anomaly of this magnitude," says Jack Connerny, a space physicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who is co-investigator for the magnetometer/electron reflectometer on the Global Surveyor, which made the measurements.

At this point, Connerny says researchers don't know how the anomalies arose. They could be the result of solidified lava from ancient volcanoes. On Earth, lava takes on the magnetic orientation of the current magnetic field as it solidifies. When the magnetic field changes, these rocks maintain their orientation and appear as anomalies. If this is the case, then the regions of magnetic disarray on Mars could help researchers understand how the magnetic field on Mars fluctuated over time. However, until the Global Surveyor collects more data about the anomalies and the surrounding topography, researchers won't be able to interpret them, says Connerny. "Right now, they are a little enigmatic," he says.

"Very interesting," muses David Stevenson, planetary physicist at the California Institute of Technology in Pasadena, but he agrees that researchers need to know more about the size and shape of the anomalies and how they are distributed across Mars--such as whether they are close to ancient volcanoes--before they can draw firm conclusions about Mars's past.

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