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Unique determination of macroscopic roughness of small airless planetary bodies from spacecraft images

Presentation #412.11 in the session Asteroids: Near-Earth Objects (Poster + Lightning Talk)

Published onOct 23, 2023
Unique determination of macroscopic roughness of small airless planetary bodies from spacecraft images

Most of our understanding of small bodies in the solar system comes from Earth-based or near-Earth telescopes. Particularly, photometry allows determination of key physical parameters of planetary surfaces, such as macroscopic roughness, porosity, single scattering albedo and single particle phase function. However, the effects of these parameters are highly convoluted, and high phase angle observations are typically needed to disentangle their effects on disk-integrated telescopic data.

Disk-resolved images of small airless bodies taken from spacecraft provide an alternate way to accurately determine a key photometric parameter - the macroscopic roughness - which encompasses facets ranging in size from aggregates of particles to mountains, craters and ridges. Since its effect is scale-invariant, roughness yields insights into the texture of the surface below the camera resolution, and provides a way to quantitatively compare textures of various airless bodies in the solar system. More importantly, the roughness derived from the disk-resolved images can then be plugged into models like the Hapke model to help constrain other physical parameters when high phase angle observations are not available.

In this project, we are using disk-resolved spacecraft images of a diverse set of asteroids - Dimorphous, Bennu, Ryugu, Vesta - and comet 67P. This analysis requires reflectance data that span a wide range of incidence/emission angle, which can be easily extracted from a scan along a disk-resolved image. We compare these reflectance curves to models generated via the the crater-roughness model, which calculates reflectance of a surface filled with rough facets by a crater-like shape defined by a depth-to-radius ratio (q) and fractional coverage. The q parameter, which relates to the surface roughness, can then be incorporated into the Hapke model which is commonly used for analysis of disk-integrated photometric data from telescopes.

This exercise will not only help make the analysis of remote photometric observations of asteroids and comets easier, but also allow comparison of surface roughness of these small bodies to other airless bodies in the solar system.

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