UCLA

This dissertation examines the influence of solar radiation on near-Earth asteroids (NEAs); it investigates thermal properties and examines changes to orbits caused by the process of anisotropic re-radiation of sunlight called the Yarkovsky effect.

For the first portion of this dissertation, we used geometric albedos p_V and diameters derived from the Wide-Field Infrared Survey Explorer (WISE), as well as geometric albedos and diameters from the literature, to produce more accurate diurnal Yarkovsky drift predictions for 540 NEAs out of the current sample of ~8800 known objects. These predictions are intended to assist observers, and should enable future Yarkovsky detections.

The second portion of this dissertation introduces a new method for detecting the Yarkovsky drift. We identified and quantified semi-major axis drifts in NEAs by performing orbital fits to optical and radar astrometry of all numbered NEAs. We discuss a subset of 54 NEAs that exhibit some of the most reliable and strongest drift rates. Our selection criteria include a Yarkovsky sensitivity metric that quantifies the detectability of semi-major axis drift in any given data set, a signal-to-noise metric, and orbital coverage requirements. In 42 cases, the observed drifts (10^-3 AU/Myr) agree well with numerical estimates of Yarkovsky drifts. This agreement suggests that the Yarkovsky effect is the dominant non-gravitational process affecting these orbits, and allows us to derive constraints on asteroid physical properties. We define the Yarkovsky efficiency f_Y as the ratio of the change in orbital energy to incident solar radiation energy, and we find that typical Yarkovsky efficiencies are ~10^-5.

The final portion of this dissertation describes the development of and results from a detailed thermal model of potentially hazardous asteroid (29075) 1950 DA. This model combines radar-derived shape models of the object and fourteen 12 micron observations by the WISE spacecraft. The observations were taken at a single phase angle, and this thermophysical model constrains K to less than 0.01 W m^-1 K^-1. By running Monte Carlo simulations that varied diameter and thermal conductivity over a reasonable range of values, thermal inertia was constrained to be less than 110 J m^-2 s^-0.5 K^-1. This value is consistent with other measurements of thermal conductivity and inertia for near-Earth asteroids.

This dissertation represents a new and original contribution to the study of NEAs. We increased the number of published predicted Yarkovsky drifts by an order of magnitude, increased the number of Yarkovsky detections by a factor of four, and developed new code to derive thermophysical parameters of asteroids that in turn drive their susceptibility to the Yarkovsky drift.