A thermal model for near-Earth asteroids

Abstract

It has become common practice in studies of the thermal emission from near-Earth asteroids to employ thermal models developed on the basis of infrared observations of large, main-belt asteroids. However, near-Earth asteroids are relatively small and are expected to have less dusty, "rockier", surfaces with higher thermal inertias than main-belt asteroids. Furthermore, they tend the have irregular shapes, and are often observed at large solar phase angles. compared to main-belt objects. Therefore, the applicability of the commonly used asteroid thermal models to these objects ist not self-evident. Radiometric data in the 4-20 µm range of several near-Earth asteroids are compared with model predictions of the thermal emission. For all the objects considered both the "Standard" and "Fast Rotating" thermal models produce poor fits to the observational data. Simple modifications to the Standard Thermal Model are described that liead to significantly improved fits to the data. Revised estimates of the albedos and sizes of a number of near-Earth asteroids are derived using the resulting new thermal model with an empirically derived calibration parameter, and compared with existing data from other sources. The new model is proposed as a default simple thermal model for estimating albedos and diameters of near-Earth asteroids.