October 18, 2017

03.04.10- Messenger and the Mysteries of Mercury.

Neutral & Ionized Sodium as seen by the Messenger spacecraft. (Credit: NASA).

Neutral & Ionized Sodium as seen by the Messenger spacecraft. (Credit: NASA).

 

   The history of the inner most planet is an enduring puzzle to planetary scientists. On September 29th of last year, NASA’s Messenger spacecraft passed within 142 miles of Mercury’s night side in an orbital “tweak” on its way to eventual orbital insertion on March 18th, 2011. During that pass, the spacecraft once again measured the trailing exo-sphere, a thin trailing wind made of sodium, potassium, calcium, and magnesium. This “mercurial wind” is replenished either by solar radiation pressure, micro-meteoroid impact, or a combination of the two. The mystery is the ratios of calcium and magnesium observed that is significantly different than predicted. Mercury is a rocky iron world that is over half core and believed to have only a thin mantle and crust. Either Mercury formed that way early in its history, a young Sun boiled away a majority of silicates, or Mercury suffered a major crust stripping impact. Further evidence for the impact scenario comes from Messenger’s neutron spectrometer, which registered a conspicuous lack of low-energy neutrons emanating from the surface of the planet itself. This is highly suggestive of an iron and titanium rich surface similar to what’s found in basaltic rock on the lunar near side. Whatever the case, plenty of surprises await us as Messenger takes up permanent residence around Mercury next year!

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