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How Mercury is like Saturn (and other surprises from NASA's orbiter)

NASA's Messenger craft has been orbiting Mercury for 88 days. Among its findings: a Saturn-like magnetic field, high concentrations of sulfur, and some support for the notion there is water ice in shadowed craters.

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In this photo, NASA's Messenger craft was high above Mercury's southern hemisphere on May 24, and shows Mercury forming a beautiful crescent shape. Mercury's origins are more like Saturn's than Earth, scientists said Thursday.

Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/NASA/Reuters

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The planet Mercury, long a backwater on the solar-system exploration itinerary, is turning out to be one hot destination.

New observations of the first rock from the sun – gathered by NASA's Messenger orbiter and described Thursday – reveal some surprises.

For example, the planet's mineral makeup is far different from the composition researchers were expecting. And its magnetic field in some ways is more like Saturn's than that of Earth, the only other terrestrial planet with an active internal dynamo generating such fields.

The report from the orbiter also gave some support to a hypothesis based on previous radar observations that northern craters whose floors are in perpetual shadow may in fact be loaded with water ice.

Until now, no spacecraft has orbited Mercury. All that planetary scientists have had to go on from previous spacecraft were results from three Mariner 10 flybys in the 1970s and three Messenger flybys as the craft made its way from Earth to Mercury.

But what a difference an orbiter makes. Just as orbiters sent to the moon, including NASA's Lunar Reconnaissance Orbiter, have revealed an object far more dynamic than previously thought even a decade ago, so Messenger is showing that Mercury is more than "the burnt-out cinder of the solar system," as some in the planetary-science community had characterized it.

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