Asteroid thermal modeling in the presence of reflected sunlight with an application to WISE/NEOWISE observational data

TL;DR

This paper improves asteroid thermal models by incorporating reflected sunlight and Kirchhoff's law, leading to more accurate and realistic estimates of asteroid properties from WISE/NEOWISE data.

Contribution

It introduces a new derivation of the NEATM model that accounts for reflected sunlight and surface properties, and proposes a curve fitting method independent of visible observations.

Findings

Revised asteroid diameter estimates with larger error margins.

Demonstrated the importance of surface material properties on thermal modeling.

Showed that previous NEOWISE results underestimated errors and assumptions.

Abstract

This study addresses thermal modeling of asteroids with a new derivation of the Near Earth Asteroid Thermal (NEATM) model which correctly accounts for the presence of reflected sunlight in short wave IR bands. Kirchhoff's law of thermal radiation applies to this case and has important implications. New insight is provided into the eta parameter in the NEATM model and it is extended to thermal models besides NEATM. The role of surface material properties on eta is examined using laboratory spectra of meteorites and other asteroid compositional proxies; the common assumption that emissivity e = 0.9 in asteroid thermal models may not be justified and can lead to misestimating physical parameters. In addition, indeterminacy in thermal modeling can limit its ability to uniquely determine temperature and other physical properties. A new curve fitting approach allows thermal modeling to be done independent of visible band observational parameters such as the absolute magnitude H. These new thermal modeling techniques are applied to observational data for selected asteroids from the WISE/NEOWISE mission. The previous NEOWISE analysis assumes Kirchhoff's law does not apply. It also deviates strongly from established statistical practice and systematically underestimates the sampling error inherent in observing potentially irregular asteroids from a finite sample of observations. As a result, the new analysis finds asteroid diameter and other physical properties that have large differences from published NEOWISE results, with greatly increased error estimates. NEOWISE results have a claimed +/-10% accuracy for diameter estimates, but this is unsupported. ABSTRACT CONTINUED IN PDF...