Mercury: Thermal Modeling and Mid-infrared (5–12 μm) Observations
摘要
We present and use a new rough-surface thermal model to aid in the analysis of new mid-infrared spectral measurements of Mercury from 5–12.5 μm. The model calculates spatially resolved thermal emission from slowly rotating, airless bodies. The Mercury data contain the first spectral measurements of Mercury between 5–7.5 μm, a region not accessible from ground-based telescopes, and are also the first observations of Mercury to be made while flying on the Kuiper Airborne Observatory (KAO). They were obtained with the High- efficiency Infrared Faint Object Grating Spectrometer (HIFOGS). Our rough surface thermal model which best fit the KAO data has a Hapke θ of 20°. A strong 5-μm emission feature was present during both observing periods. We suggest the 5-μm excess may be a result of near surface thermal gradients in regolith materials with a 30 to 100-μm grainsize, but cannot entirely rule out an observational artifact resulting from our instrumentation or the telescope on the KAO. Other features in the spectra are consistent with a feldspathic and feldspathoidal surface composition.