The Effect of Aspect Changes on Near-Earth Asteroid Phase Curves

TL;DR

This paper shows that near-Earth asteroid phase curves are influenced not only by surface properties but also significantly by shape, rotation, and viewing geometry, affecting the interpretation of observational data.

Contribution

It introduces a method to model and quantify the aspect-related uncertainties in asteroid phase curves, highlighting the importance of considering shape and orientation effects.

Findings

Aspect changes can significantly alter phase curves.

Ignoring aspect effects can lead to underestimated uncertainties.

Software tools are provided for aspect-related phase curve analysis.

Abstract

Phase curves of asteroids are typically considered to depend solely on the scattering properties of airless particulate surfaces and the size of the object being studied. In this study, we demonstrate the additional dependence of phase curves on object shape, rotation pole orientation, and viewing geometry over an apparition. Variations in the phase curve of near-Earth asteroid (159402) 1999 AP10 over its apparition from July 2020 - January 2021 are verified to be due to aspect changes over the apparition. This is achieved through shape modelling of the asteroid and simulation of the phase curve over the apparition. We present simulations of asteroid phase curves over a range of geometries to understand the potential magnitude of this aspect effect, and under which circumstances it can begin to dominate in the phase curves. This dependence on aspect may introduce significant additional uncertainty in the properties derived from phase curve data. We provide and demonstrate software code to estimate the aspect-related uncertainty in near-Earth asteroid phase curves through simulation and model fitting of a randomly generated sample of ellipsoidal asteroid models over the observed viewing geometry. We demonstrate how ignoring this effect may lead to misleading interpretations of the data and underestimation of uncertainties in further studies, such as those in the infrared that use phase curve derived parameters when fitting physical properties of an asteroid.