Forgot this paper from Journal of Geophysical Research-Planets. In the May issue (vol. 130 #5):
Martin, A. C. Emery, J. P. Loeffler, M. et al. Mid-Infrared Reflectance and Emissivity Spectra of High Porosity Regoliths 2024JE008331
This one’s kind of important. We examine all sorts of astronomical bodies in the infrared, as lots of molecules have spectral features there. Spotting a spectral line or absorption means we’ve identified a chemical component, right? Right? For stars, nebulae, the interstellar medium, and other gases/plasmas, this is pretty straightforward. But for condensed matter (i. e., rock), not so fast. Solid objects have secondary effects; these include those due to particle size, which become relevant at these longer wavelengths. Martin et al., as have many before them, treat the problem of solid-particle effects. Gee, solid particles- sounds like asteroid regolith! (Along with comet dust mantles, the Mars surface, anything that forms ice frost, etc.) And there are thermal effects too: packed regolith doesn’t heat and cool like solid rock, nor loose regoliths. Empty space is an insulator, solid matter is not, and packed particles are in between. All told, the question of infrared appearances (vs. asteroid reality) is not what-you-see-is-what-you-get. But Martin et al. may get us one step forward.