Letter to the Editor

On the density of EKOs and related objects

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: author@mpifr-bonn.mpg.de
² Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany e-mail: bertoldi@astro.uni-bonn.de
³ IRAM, Domaine Universitaire de Grenoble, 300 rue de la piscine, 38406 St. Martin d'Hères, France e-mail: thum@iram.fr

Received: 25 May 2005
Accepted: 11 August 2005

Abstract

Recently published mass determinations of EKO binaries, combined with photometric size determinations, allow to derive a mean density of the distant minor planets of ≈0.2 g cm^-3. This agrees well with the nuclear density of 1P/Halley of 0.26 g cm^-3, determined in the Giotto mission, and it suggests that these low density objects are essentially undifferentiated planetesimals.