Turn the heat up - A first look at MESSENGER's near-infrared spectra of Mercury using new high-temperature emissivity measurements

Analyzing the surface composition of Mercury's regolith from remote-sensing measurements is a challenging task. In support of the National Aeronautics and Space Agency's MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission and especially in preparation for the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument on the BepiColombo mission of the European Space Agency and the Japan Aerospace Exploration Agency, we are developing a Planetary Emissivity Laboratory (PEL) at Deutsches Zentrum für Luft- und Rahmfahrt (DLR) in Berlin. The PEL allows measurement of the emissivity of Mercury-analogue materials at grain sizes smaller than 25 μm and at temperatures of more than 400°C, typical for Mercury's low-latitude dayside. The PEL development follows a multi-step approach. We have already obtained emissivity data at mid-infrared wavelengths that show significant changes in spectral behavior with temperature indicative of changes in the crystal structure of the samples. We are currently installing a new calibration target that will allow the acquisition of emissivity data over the full wavelength range from 1 to 50 micrometer with good signal-to-noise ratio. Here we present initial data in the range 1 to 1.4 micrometer, the near-infrared wavelength coverage of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument on MESSENGER. Even these early PEL measurements have important implications for the analysis of the spectral observations obtained during MESSENGER's first Mercury flyby on 14 January 2008 as well as the data to be obtained during the probe's second Mercury flyby on 6 October.