After its first year in orbit around Mercury, NASA's MESSENGER spacecraft has yielded data on the planet's structure: the iron core is larger than previously thought and, unusually, is encased in a relatively thin shell of iron sulphide.
Maria Zuber at the Massachusetts Institute of Technology in Cambridge and her colleagues built a gravity model for the planet using measurements of tiny changes in the spacecraft's orbit. Combining this model with data on the planet's topography and spin, the authors found that as much as 85% of Mercury's radius is taken up by its dense iron core. This, along with the iron sulphide shell, helps to explain the planet's gravity field.
Another paper from Zuber and colleagues suggests that volcanic and tectonic activity persisted well past Mercury's first several hundred million years. This could explain surface features observed by the team, such as uplifted or tilted basin floors.
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What lies beneath Mercury's surface. Nature 483, 513 (2012). https://doi.org/10.1038/483513b
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DOI: https://doi.org/10.1038/483513b
