Near surface bulk density estimates of NEAs from radar observations and permittivity measurements of powdered geologic material

Dylan Hickson, Alexandre Boivin, Michael G. Daly, Rebecca Ghent, Michael C. Nolan, Kimberly Tait, Alister Cunje, Chun An Tsai

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

The variations in near-surface properties and regolith structure of asteroids are currently not well constrained by remote sensing techniques. Radar is a useful tool for such determinations of Near-Earth Asteroids (NEAs) as the power of the reflected signal from the surface is dependent on the bulk density, ρbd, and dielectric permittivity. In this study, high precision complex permittivity measurements of powdered aluminum oxide and dunite samples are used to characterize the change in the real part of the permittivity with the bulk density of the sample. In this work, we use silica aerogel for the first time to increase the void space in the samples (and decrease the bulk density) without significantly altering the electrical properties. We fit various mixing equations to the experimental results. The Looyenga–Landau–Lifshitz mixing formula has the best fit and the Lichtenecker mixing formula, which is typically used to approximate planetary regolith, does not model the results well. We find that the Looyenga–Landau–Lifshitz formula adequately matches Lunar regolith permittivity measurements, and we incorporate it into an existing model for obtaining asteroid regolith bulk density from radar returns which is then used to estimate the bulk density in the near surface of NEA's (101955) Bennu and (25143) Itokawa. Constraints on the material properties appropriate for either asteroid give average estimates of ρbd=1.27±0.33g/cm3 for Bennu and ρbd=1.68±0.53g/cm3 for Itokawa. We conclude that our data suggest that the Looyenga-Landau-Lifshitz mixing model, in tandem with an appropriate radar scattering model, is the best method for estimating bulk densities of regoliths from radar observations of airless bodies.

Original languageEnglish (US)
Pages (from-to)16-24
Number of pages9
JournalIcarus
Volume306
DOIs
StatePublished - May 15 2018
Externally publishedYes

Keywords

  • Asteroid Bennu
  • Asteroids
  • Radar observations
  • Regoliths
  • surfaces

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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