Testing general relativity with high-precision measurements of asteroid trajectories

Funding

We have received two 5-year grants from the Division of Astronomical Sciences of the National Science Foundation (AST-0606953 and AST-1109772) to fund a long-term investigation of the trajectories of asteroids. UCLA leads the investigation.

Program description

The trajectories of some asteroids are affected by sunlight, by the fact that the Sun is not perfectly spherical, and because of effects described in Albert Einstein's theory of General Relativity. Since 2001, we have been tracking the motion of asteroids that make very close approaches to the Sun with Arecibo radar measurements. Our goal is to detect anomalies in asteroid trajectories. We will test Einstein's theory, learn more about the precise shape of the Sun, and measure the influence of sunlight on asteroid trajectories.

Objects observed so far

Five suitable asteroids have been observed on at least two occasions, making these targets prime candidates for the realization of program goals (click on the links to learn more about individual asteroids):

Object First detection Second detection Third detection
1999 KW4 2001 May 25-28 2002 Jun 01-02
2000 BD19 2006 Feb 26-27 2007 Dec 22-23
1999 MN 2004 Jul 22-23 2005 May 30-31
1566 Icarus 2015 Jun 17-20
2000 EE14 2007 Mar 04-06 2008 Feb 28-29
2001 YE4 2002 Jan 10-11 2012 Jan 04-05 2016 Dec 28-29
2006 CJ 2012 Feb 06-07 2017 Feb 05-06
2004 KH17 2013 Jun 03
1998 TU3 2012 Aug 02

Top priority targets

Our full list of top priority targets is maintained in an online database which is updated nightly. Table columns (which can be sorted and ordered) include the orbital parameters, years of apparitions, and years of detections. In the future, this table will be fully cross-linked with the asteroid radar database at radarastronomy.org

Proposal Title and Abstract

Perihelion advance and Yarkovsky drift of near-Earth asteroids: asteroid physical properties, solar oblateness, and general relativity

Drs. Jean-Luc Margot and Jon Giorgini will obtain and interpret high-precision radar range measurements of 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 Sun's 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.

References

J.L. Margot, Candidate Asteroids for Discerning General Relativity and Solar Oblateness, American Astronomical Society, DDA meeting #34, #06.13, 2003.

J.L. Margot and J.D. Giorgini, Probing general relativity with radar astrometry in the inner solar system, Proceedings of IAU symposium 261: Relativity in Fundamental Astronomy - Dynamics, Reference Frames and Data Analysis, 261, p. 183-188, 2010.

A. H. Greenberg, J. L. Margot, A. K. Verma, P. A. Taylor, S. P. Naidu, M. Brozovic, L. A. M. Benner. Asteroid 1566 Icarus's size, shape, orbit, and Yarkovsky drift from radar observations. Astronomical Journal, in press.