An exploration of Pluto’s environment through stellar occultations

¹ LESIA-Observatoire de Paris, CNRS, Univ. Pierre et Marie Curie, Univ. Paris-Diderot, 92190 Meudon, France
e-mail: francoise.roques@obspm.fr
² Department of Astronomy, New Mexico State University, PO Box 30001, MSC 4500, Las Cruces NM 88003-8001, USA
³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, 19001 Casilla, Santiago 19, Chile
⁴ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
⁵ Université de Franche-Comté, Institut UTINAM, CNRS/INSU, UMR 6213, 25030 Besançon Cedex, France
⁶ Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
⁷ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁸ Observatório do Valongo/UFRJ, Ladeira Pedro Antonio 43, CEP 20. 080-090 Rio de Janeiro RJ, Brazil
⁹ Observatório Nacional/MCTI, R. General José Cristino 77, CEP 20921-400 Rio de Janeiro RJ, Brazil
¹⁰ Centro Universitário Estadual da Zona Oeste, Av. Manual Caldeira de Alvarenga 1203, CEP 23. 070-200 Rio de Janeiro RJ, Brazil
¹¹ Observatoire de Genève, 1290 Sauverny, Switzerland
¹² International Occultation Timing Association, European Section, 30459 Hannover, Germany

Received: 5 May 2013
Accepted: 3 December 2013

Abstract

Context. Pluto has five known satellites with diameters ranging from ~1200 km down to ~40 km, a possible outcome of a collisional origin. Smaller objects probably exist and may maintain tenuous rings, thus representing hazards during the New Horizons flyby of July 2015.

Aims. The goal is to provide an upper limit for the numbers of unseen small bodies and/or equivalent widths of putative Pluto rings.

Methods. We use a Pluto stellar appulse on April 10, 2006, and a stellar occultation by the dwarf planet on June 14, 2007, to scan Pluto’s surroundings.

Results. Our best data set places a 3σ upper limit of 0.3 km for the radius of isolated moonlets that we can detect. In the absence of detection, we derive an upper limit of 15 000 for the number of such bodies at distances smaller than ~70 000 km from Pluto’s system barycenter. We place a 3σ upper limit of typically 30−100 m for the equivalent width of ring material at barycentric distances ranging from 13 000 to 70 000 km. This limit applies for narrow rings only, i.e. less than about 10 km in width.