The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft is a scientific investigation of the planet Mercury by NASA. Mercury is still the least explored terrestrial planet and understanding it and how it was formed is essential to understanding the other terrestrial planets and their evolution. The only other visit to the planet was the Mariner 10 spacecraft in 1975, giving us some hints on its average density (the second greatest of all the planets), the composition of its atmosphere (thinnest of the terrestrial planets), the fact that it possesses a global magnetic field, and its extreme variations in temperature. MESSENGER mission entered Mercury orbit in March 2011 and started the nominal mission on on April 2011: data collected during the three initial and the flybys are analyzed to better understand this world. The primary mission was completed on March 2012, having collected close to 100,000 images and more than 3 million spectra in the wavelength range from 320 nm to 1450 from the Mercury Atmospheric and Surface and Composition Spectrometer (MASCS) instrument.
After running out of propellant for course adjustments, MESSENGER entered its expected terminal phase of orbital decay in late 2014. MESSENGER continued studying Mercury during its decay period producing the high spatial resolution resolution data. The spacecraft crashed onto the surface of Mercury on April 30, 2015, at 19:26 GMT, at a velocity of 14080 km/h in an estimated location at 54.4° N, 149.9° W on Suisei Planitia. NASA confirmed the end of the MESSENGER mission at 19:40 GMT after NASA's Deep Space Network failed to detect the spacecraft's reemergence from behind Mercury.
MASCS Data analysis & results
In 2010 NASA has selected us as participating scientists for the MESSNGER mission. We have since then supported the MESSENGER team with data processing and high temperature spectroscopy at PEL.
Under the hypothesis that surface compositional information can be effectively derived from spectral reflectance measurements with the use of statistical techniques, we employ unsupervised hierarchical clustering analyses to identify and characterize spectral units from all orbital observations made with MASCS during the primary mission. The results indicate a dichotomy in major units, with one spectral unit in the polar regions and a spectrally distinct unit in equatorial areas. The spatial extent of the polar unit in the northern hemisphere shows a generally good correlation with the northern volcanic plains and with the regions of enhanced potassium abundance as mapped by the Gamma-Ray Spectrometer on MESSENGER. This asymmetry indicates that peak surface temperature, although potentially important, is not the only factor that contributes to the different spectral character of the surface units. We conclude that compositional differences also contribute to the spectral differences between the two major units on the surface of Mercury identified with this hierarchical clustering approach.
The work on the MESSENGER mission is essential as preparation for the data analysis of the MERTIS instrument. MERTIS will provide us with a high complementary dataset that will enable us to understand better the mineralogy of Mercury.