YORP effect on real objects

I. Statistical properties

¹ Dipartimento di Fisica, Università di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy e-mail: paolicchi@df.unipi.it
² Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, HI-96822 Honolulu, USA e-mail: micheli@ifa.hawaii.edu

Received: 25 October 2007
Accepted: 15 July 2008

Abstract

Context. The intensity of the YORP (Yarkovsky, O'Keefe, Radzievskii, and Paddack) effect and its ability to affect the rotational properties of asteroids depend mainly on the size of the body and on its shape. At present, we have a database of about 30 well-defined shapes of real minor bodies (most of them asteroids, but also planetary satellites and cometary nuclei).

Aims. In this paper we perform a statistical analysis of how the YORP effect depends on the shape.

Methods. We used the Rubincam approximation (i.e. neglecting the effects of a finite thermal conductivity).

Results. We show that, among real bodies, the distribution of the YORP types, according to the classification of Vokrouhlický and Čapek, is significantly different from the one obtained in the same paper from theoretical modeling of shapes. A new “type” also comes out. Moreover, we show that the types are strongly correlated with the intensity of the YORP effect (when normalized to eliminate the dependence on the size, and thus only related to the shape).