THERMAL INFRARED LABORATORY STUDIES OF ANALOG MATERIALS: IMPLICATIONS FOR INTERPRETING REMOTE SENSING OBSERVATIONS OF SOLAR SYSTEM AIRLESS BODIES (Invited Presentation)

The surfaces of most Solar System airless bodies are dominated by particulate regolith materials. The heat or emitted radiation that we measure using telescopes and spacecraft originates from the upper hundreds of microns of regolith of these airless bodies. Early laboratory studies and radiative transfer modeling demonstrated that the vacuum environment in the near-surface regolith of airless bodies creates a thermal gradient, which causes known spectral features to shift position and change in contrast. The thermal gradient and how much spectral features shift and change in contrast are governed by key regolith properties including composition, albedo, particle size, and porosity.

Thus, to better interpret thermal infrared (TIR) remote sensing observations of Solar System airless bodies, we need laboratory measurements of well-characterized analog materials measured under the appropriate near-surface conditions. Near-surface environments for airless bodies can be simulated using bespoke vacuum environment chambers like the Planetary Analogue Surface Chamber for Asteroid and Lunar Environments (PASCALE). PASCALE is capable of simulating near-surface conditions for a range of Solar System bodies by varying the atmospheric pressure and temperature inside the chamber and the incident solar-like irradiation on the sample. By varying the near-surface environment, the thermal gradient in the upper hundreds of microns of the sample is varied, which affects the position and contrast of diagnostic features in TIR spectra. As an example, lunar-like conditions are simulated by removing atmospheric gases within the chamber (pressure < 10^-4 mbar), heating the sample from below to 353K, and heating the sample from above until the estimated brightness temperature of the sample is ~390K. The emitted radiation from the sample is then passed to a Bruker VERTEX 70V Fourier Transform Infrared (FTIR) spectrometer capable of measuring thermal infrared wavelengths (~5-50 microns or 2000-200 cm^-1).

Here we present laboratory thermal infrared emissivity spectra of lunar and asteroid analogs measured under lunar- and asteroid-like near-surface conditions and discuss the implications for the interpretation of remote sensing observations to better constrain composition and physical properties.