Hydrogen Concentrations near Mercury’s North Pole: New Measurements from MESSENGER’s Low-Altitude Campaign

Tuesday, 16 December 2014
David J Lawrence, Johns Hopkins University, Baltimore, MD, United States, Patrick N Peplowski, Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, William C Feldman, Planetary Science Institute, Planetary Science Institute, Los Alamos, NM, United States and Sean C Solomon, Columbia University of New York, Palisades, NY, United States
Definitive measurements of enhanced hydrogen concentrations linked to permanently shaded regions (PSRs) near Mercury’s north pole were made with MESSENGER’s Neutron Spectrometer (NS). These hydrogen concentrations were reported only as variations with latitude, in part because the NS data set from MESSENGER’s first orbital year had a spatial resolution of around 650 km for regions poleward of 75ºN. As a consequence, the data for these initial measurements did not allow for investigations of variations of hydrogen with longitude or enable the specification of hydrogen concentrations for individual polar deposits. Now, with new NS data that have been acquired or will be acquired during MESSENGER’s low-altitude campaign, such questions on spatial variability can be addressed. First, the average altitude in polar regions (latitude > 75ºN) will be ~200 km compared with the 430 km average altitude during the first year of data collection. This lower altitude will improve the spatial resolution by a factor of 2 and provide for a quantification of the longitudinal variation of the north polar hydrogen enhancement. Second, during early September 2014, the MESSENGER spacecraft will pass over an isolated group of three PSRs (in the craters Desprez, Bechet, and Qui Ying) at altitudes of less than 100 km. If these PSRs have sufficient water ice, as is expected on the basis of radar backscatter data, then the increase in epithermal neutron signal strength and spatial resolution may allow this group of PSRs to be spatially resolved.