October 20, 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!

10.10.09: An Active Mercury?

An atmosphere. Magnetosphere. Signs of recent geological activity…is it Mars? Europa? Some far off exo-planet? Nope…its none other than Mercury, a visual twin of our own Moon and long thought of as just as inactive. The past three flybys of NASA’s Messenger spacecraft have revealed a world of dynamic activity. First, there is Mercury’s on-again, off-again magnetic field, a sign that it may possess an active core. Now that 95%+ of the surface has been visualized, a picture is emerging of a crater pocked surface that has also been shaped by recent volcanism. Finally, Messenger has picked up tenuous traces of magnesium out-gassing from the planet as a result of the intense solar radiation bombarding the sun-ward side, contributing to a tenuous trailing exosphere. The 3rd pass last week was the closest yet, and revealed more stunning photos of what is now the tiniest “planet…” Messenger will enter a permanent orbit in 2011. Google Mercury, anyone?