On March 17, MESSENGER (MErcury Surface, Space Environment, GEochemistry, and Ranging) completed its one-year primary mission, orbiting Mercury,
capturing nearly 100,000 images, and recording data that reveals new information about the planet's core, topography, and the mysterious radar
bright material in the permanently shadowed areas near the poles.
The findings are presented in two papers published online in Science Express.
"Mercury is the last unexplored planet," said UC Santa Barbara physics professor emeritus Stanton Peale, who devised the procedure used for
detecting whether or not Mercury had a liquid core. The way Mercury was formed, he said, may show some constraints on the formation of the solar system.
For one thing, Mercury's core is larger than expected almost 85 percent of the planetary radius.
The Earth's core, in contrast, is just over half of the planet's radius.
Additionally, Mercury appears to have a more complex core than Earth's a solid iron sulfide layer that is now part of the mantle,
which encases a liquid core, which may float on a solid inner core.
The scientists, led by MIT researchers David E. Smith and Maria T. Zuber, also found that Mercury's solid outer core and liquid inner
core contain more iron than Earth, relative to the whole planet, which influences the way Mercury's magnetic field was generated.
However, Peale noted that the surface is comprised of lighter elements.
"We didn't expect so much sulfur," he said, adding that there was almost no iron found on the surface of the planet.
With no iron, the volcanic surface rocks are too light to have come from a mantle with the large average density
derived for the internal structure. This led to the concept of a two-layer mantle with a light upper silicate layer,
which could provide the low-density surface material over a dense iron sulfide layer.
In the larger picture, the presence of inordinately large amounts of sulfur on the surface indicates that Mercury's
formation was not as orderly as some scientists had previously assumed, according to Peale. "Mercury is composed of
material that had condensed over a wide range from the Sun," he said.
The double image at the top of the post shows Mercurys true colors on the left, and an exaggerated false-color image on the right taken
using 11 different color filters. The video was made the same way. Bringing out the color this way can help geologists make guesses about the
age and composition of the terrain. Credit: NASA
Other findings include a precise topographic model of the planet's northern hemisphere, which reveals a smaller spread in elevations compared to
those of Mars or the Moon.
Additionally, radar-bright features at the poles located in areas of permanent shadow have been found to be consistent with a water-ice
hypothesis; however the notion has yet to be tested further with MESSENGER's neutron spectrometer.
MESSENGER is already on the next phase of its investigations: an extended year-long mission that includes more comprehensive and more
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