Multiple Asteroid Systems: Dimensions and Thermal Properties from Spitzer Space Telescope and Ground-Based Observations

TL;DR

This study uses Spitzer Space Telescope and ground-based data to analyze the sizes, compositions, and thermal properties of multiple asteroid systems, revealing insights into their surface features and internal structures.

Contribution

It provides detailed thermal modeling and compositional analysis of multiple asteroid systems, including size, albedo, and density estimates, using combined infrared and lightcurve data.

Findings

Large binary asteroids have low thermal inertia and thick regolith layers.

Smaller asteroids show weaker mineral emission lines, indicating coarser regolith.

Densities vary from 0.7 to 3.2 g/cm3 across different asteroid types.

Abstract

Photometric lightcurves were also obtained for 14 of them during the Spitzer observations to provide the context of the observations and reliable estimates of their absolute magnitudes. The extracted mid-IR spectra were analyzed using a modified standard thermal model (STM) and a thermophysical model (TPM) that takes into account the shape and geometry of the large primary at the time of the Spitzer observation. We derived a reliable estimate of the size, albedo, and beaming factor for each of these asteroids, representing three main taxonomic groups: C, S, and X. For large (volume-equivalent system diameter Deq $\lt$ 130 km) binary asteroids, the TPM analysis indicates a low thermal inertia ($\Gamma$ < $\sim$100 J s-1/2K-1m-2) and their emissivity spectra display strong mineral features, implying that they are covered with a thick layer of thermally insulating regolith. The smaller (surface-equivalent system diameter Deff $\lt$17 km) asteroids also show some emission lines of minerals, but they are significantly weaker, consistent with regoliths with coarser grains, than those of the large binary asteroids. The average bulk densities of these multiple asteroids vary from 0.7-1.7 g/cm3 (P-, C- type) to $\sim$2 g/cm3 (S-type). The highest density is estimated for the M-type (22) Kalliope (3.2 $\pm$ 0.9 g/cm3). The spectral energy distributions (SED) and emissivity spectra, made available as a supplement document, could help to constrain the surface compositions of these asteroids.