Dielectric Properties of Vesta's Surface as Constrained by Dawn VIR Observations

TL;DR

This study models Vesta's surface dielectric properties using Dawn VIR data, revealing a relatively constant dielectric constant and porosity estimates, and suggests surface roughness influences radar backscatter more than dielectric variations.

Contribution

First dielectric model of Vesta's surface based on VIR data, linking surface properties to radar backscatter characteristics.

Findings

Dielectric constant ranges from 2.3 to 2.5 across Vesta's surface.

Surface porosity estimated at approximately 55%.

Radar backscatter mainly influenced by surface roughness.

Abstract

Earth and orbital-based radar observations of asteroids provide a unique opportunity to characterize surface roughness and the dielectric properties of their surfaces, as well as potentially explore some of their shallow subsurface physical properties. If the dielectric and topographic properties of asteroid's surfaces are defined, one can constrain their surface textural characteristics as well as potential subsurface volatile enrichment using the observed radar backscatter. To achieve this objective, we establish the first dielectric model of asteroid Vesta for the case of a dry, volatile-poor regolith--employing an analogy to the dielectric properties of lunar soil, and adjusted for the surface densities and temperatures deduced from Dawn's Visible and InfraRed mapping spectrometer (VIR). Our model suggests that the real part of the dielectric constant at the surface of Vesta is relatively constant, ranging from 2.3 to 2.5 from the night- to day-side of Vesta, while the loss tangent shows slight variation as a function of diurnal temperature, ranging from 0.006 to 0.008. We estimate the surface porosity to be ~55% in the upper meter of the regolith, as derived from VIR observations. This is ~12% higher than previous estimation of porosity derived from previous Earth-based X- and S-band radar observation. We suggest that the radar backscattering properties of asteroid Vesta will be mainly driven by the changes in surface roughness rather than potential dielectric variations in the upper regolith in the X- and S-band.