Constraints on the near-Earth asteroid obliquity distribution from the Yarkovsky effect

¹ Department of Mechanical & Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ, UK
e-mail: Chiara.Tardioli@strath.ac.uk
² Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
³ School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
⁴ Department of Physics and Electronics, University of Puerto Rico at Humacao, 00792 Humacao, Puerto Rico
⁵ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁶ Planetary Science Division, Science Mission Directorate, NASA Headquarters, Washington, DC 20546, USA

Received: 9 June 2017
Accepted: 3 September 2017

Abstract

Aims. From light curve and radar data we know the spin axis of only 43 near-Earth asteroids. In this paper we attempt to constrain the spin axis obliquity distribution of near-Earth asteroids by leveraging the Yarkovsky effect and its dependence on an asteroid’s obliquity.

Methods. By modeling the physical parameters driving the Yarkovsky effect, we solve an inverse problem where we test different simple parametric obliquity distributions. Each distribution results in a predicted Yarkovsky effect distribution that we compare with a χ² test to a dataset of 125 Yarkovsky estimates.

Results. We find different obliquity distributions that are statistically satisfactory. In particular, among the considered models, the best-fit solution is a quadratic function, which only depends on two parameters, favors extreme obliquities consistent with the expected outcomes from the YORP effect, has a 2:1 ratio between retrograde and direct rotators, which is in agreement with theoretical predictions, and is statistically consistent with the distribution of known spin axes of near-Earth asteroids.