EDP Sciences
Free access
Volume 500, Number 2, June III 2009
Page(s) 909 - 916
Section Planets and planetary systems
DOI http://dx.doi.org/10.1051/0004-6361/200811301
Published online 08 April 2009
A&A 500, 909-916 (2009)
DOI: 10.1051/0004-6361/200811301

The trans-Neptunian object size distribution at small sizes

R. Gil-Hutton1, J. Licandro2, N. Pinilla-Alonso3, and R. Brunetto4

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

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 q0=4.2 at larger sizes to $q_1=2.40\pm0.3$ at the smaller ones, with a break radius of $r_1=35\pm15$ 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 $\approx$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 ( $r_{\rm p}<10{-}30$ m), it is possible that the exponent of the size distribution for these very small objects changes again, approaching a Donhanyi's size distribution.

Key words: Kuiper Belt -- solar system: formation -- astrochemistry -- methods: numerical

© ESO 2009