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Dark Mercury

March 8, 2016

How did Mercury get to be the darkest planet in the solar system?



This oblique image of Basho shows the distinctive dark halo that encircles the crater. The halo is composed of so-called Low Reflectance Material (LRM), which was excavated from depth when the crater was formed. (Courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)


A planet with a high carbon crust. I’m Bob Hirshon and this is Science Update.

The planet Mercury is darker than other planets, and its impact craters are rimmed with even darker material from deep underground. In the journal Nature GeoScience, Carnegie Institution cosmochemist Larry Nittler and his colleagues report that the black stuff is carbon. He says when struck by high-energy space particles, carbon emits neutrons. And detectors aboard the MESSENGER spacecraft that orbited Mercury picked up a spike of neutrons from the dark regions.

LARRY NITTLER (Carnegie Institution):

This is a very very clear correlation: as we go over these dark regions at low altitudes, we see the neutrons go up. So this is a very clear signature of carbon.


The finding lends support to a hypothesis that Mercury was once covered in a crust of graphite crystal, today obscured by volcanic rock, but blasted to the surface by the impacts of large meteorites. I’m Bob Hirshon, for AAAS, the science society.