Drs. Jean-Luc Margot and Jon Giorgini will obtain and interpret high-precision radar range measurements on twelve near-Earth asteroids (NEAs) that have trajectories strongly affected by the light of the Sun, the shape of the Sun, and general relativistic effects. Asteroid orbits are influenced by the absorption and reemission of solar energy, the so-called Yarkovsky effect. These changes to the motion will be quantified with the radar measurements in order to constrain the densities, compositions, and thermal properties of NEAs. Other perturbations to NEA orbits arise as a result of the non-uniformity of the gravitational field of the oblate Sun. The ranging data to the twelve NEAs will provide a direct probe of the mass distribution in the Suns interior by measuring changes to the asteroid trajectories. Radar tests of general relativity (GR) will also be improved by quantifying the perihelion advance of NEAs that reach deep inside the gravitational well of the Sun. The GR effects can be separated from the effects of oblateness as they have a different dependence on the size, eccentricity, and inclination of the NEA orbits. Both GR and oblateness effects can be separated from the distinct signature of the Yarkovsky drift. Most of the measurements will be performed with the planetary radar on the Arecibo telescope. Analysis of the results will make use of orbital determination software at JPL. High precision measurements in this extreme dynamical regime will provide unique observational constraints and will test current models of asteroid physics, solar physics, and fundamental physics.
