Search for satellites near comet 67P/Churyumov-Gerasimenko using Rosetta/OSIRIS images

Abstract

Context. The European Space Agency Rosetta mission reached and started escorting its main target, the Jupiter family comet 67P/Churyumov-Gerasimenko, at the beginning of August 2014. Within the Solar System small bodies context, satellite searches from approaching spacecrafts were extensively used in the past to study the nature of the visited bodies and their collisional enviroenment. Aims. During the approaching phase to the comet in July 2014, the OSIRIS instrument on board Rosetta performed a campaign aimed at the detection of objects in the vicinity of the comet’s nucleus and at the measure of their possible bound orbits. Beside the scientific purpose, the search had the additional aim of spacecraft security to avoid hazardous material in the comet’s enviroenment. Methods. Images in the red spectral domain were acquired with the OSIRIS Narrow Angle Camera following an observational strategy tailored to maximize the scientific outcome. From the acquired images, sources are extracted and displayed to search for plausible displacements of all sources from image to image. After stars identification, the remaining sources are thoroughly analysed. In order to put some constraints to the expected displacements of a potential satellite, Montecarlo simulations on the apparent motion of potential satellites within the Hill sphere have been performed. Results. We found no unambiguous detections of objects larger than ~ 6 m within ~ 20 km and larger than ~ 1 m between ~ 20 km and ~ 110 km from the nucleus. Our conclusions are consistent with independent works on dust grains in the comet’s coma and on boulders counting on the nucleus surface. Moreover, our analysis shows the comet’s outburst detected at the end of April 2014 was not strong enough to eject large objects and to place them into a stable orbit around the nucleus. Our findings underline the unlikeliness of the long–term survival of large objects around cometary nuclei.