The trans-Neptunian object size distribution at small sizes

¹ Complejo Astronómico El Leoncito - CONICET and Universidad Nacional de San Juan, Av. España 1512 sur, J5402DSP - San Juan, Argentina e-mail: rgilhutton@casleo.gov.ar
² Instituto de Astrofísica de Canarias, c/vía Láctea s/n, E38205, La Laguna, Tenerife, Spain
³ Fundación Galileo Galilei & Telescopio Nazionale Galileo, PO Box 565, 38700, S/C de La Palma, Tenerife, Spain
⁴ Institut d'Astrophysique Spatiale, Université Paris-Sud, bâtiment 121, 91405 Orsay Cedex, France

Received: 6 November 2008
Accepted: 4 March 2009

Abstract

Aims. The aim of this work is to estimate the size distribution of small Trans-Neptunian objects.

Methods. We simulate the irradiation and collisional processes affecting the surface of a Trans-Neptunian object for the first time using as a constraint the peculiar crystalline to amorphous water ice ratio observed on (136108) 2003 EL₆₁.

Results. We find that the size distribution changes its exponent from at larger sizes to at the smaller ones, with a break radius of  km. If this size distribution is applied to studying the collisional surface evolution of (136108) 2003 EL₆₁, we find that the object must be covered by a thin ice crust of ≈0.12 cm, while the original composition of the object is still present at 1.61 cm or more below the surface. This result is not affected by a collision with a large projectile that occurred by chance more than 10⁹ yr ago since after a short time the mean value obtained for the crystalline to amorphous water ice ratio is indistinguishable from the one obtained without a collision with a large projectile. Since the simulations are not sensitive to the effects of very small projectiles ( m), it is possible that the exponent of the size distribution for these very small objects changes again, approaching a Donhanyi's size distribution.