Thermal inertia of small asteroids from detailed thermophysical modeling

Abstract

We have developed and validated a thermophysical model, which gives a detailed description of the thermal emission of small asteroids. Depending on data quality, it allows the size, albedo, and thermal inertia of asteroids to be accurately determined and conclusions on the surface roughness to be drawn. The model takes direct account of the asteroid’s shape and spin state as obtained from the inversion of optical lightcurves, or from radar or spacecraft imaging. The thermal conduction equation is solved explicitly for each surface element. Roughness is modeled in terms of craters, which are described as sections of a hemisphere, with shadowing and multiple scattering of both the incident solar and thermally emitted radiation fully taken into account. Our model has been designed and tested for application in particular to near-Earth asteroids, which are often observed at large phase angles. Previous detailed thermophysical models, such as that by J. Lagerros, were validated for large main-belt asteroids, which tend to have a more regular shape than their smaller counterparts. Furthermore, they are observed at moderate solar phase angles only. We will present an overview of the model and preliminary results from its application to recent observations of near-Earth asteroids made by the authors with the NASA IRTF. Its application to forthcoming observations with the Spitzer Space Telescope will also be discussed.