December 18, 2017

03.04.10- Messenger and the Mysteries of Mercury.

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!

28.03.10- Messenger Spies High-Energy Solar Neutrons.

After a considerable hiatus, solar cycle 24 is now well under way. And this time, NASA has a key observing platform in the inner solar system; the Messenger spacecraft, bound for an insertion to orbit Mercury in March, 2011. In the intervening time, scientists at the Planetary Science Institute in Tucson, Arizona have been busying the spacecraft by monitoring the Sun from close proximity. On New Year’s Eve, 2007, the spacecraft was at about half an Astronomical Unit (A.U.) from the Sun when it had the unprecedented opportunity to study high-energy neutrons ejected from a massive solar flare. Unlike 1 minute bursts recorded in near-Earth orbit, Messenger was able to track and record these neutron bursts for 6 to 10 hours. This was accomplished by use of NASA’s Neutron Spectrometer aboard the spacecraft. From this, scientists have predicted a “decayed feedstock” of resulting protons from the flare in the 30 to 100 million electron volt range. Messenger could also clear up a long standing mystery; why do some coronal mass ejections produce huge numbers of energetic protons, while others emit relatively few? This puzzle is of more than casual interest; radiation from CMEs has damaged orbiting satellites in the past, and is of prime concern for space based astronauts. Once Messenger is in permanent orbit about Mercury, it will also have a prime vantage point to monitor the Sun close up for a year uninterrupted. And just in time for a peak in the solar maximum!