Search for satellites near (21) Lutetia using OSIRIS/Rosetta images

On 2010 July 10 the ESA Rosetta mission flew by the large asteroid (21) Lutetia. One of the scientific goals of the onboard OSIRIS instrument was the search for satellites of the asteroid, with more than 20 images specifically dedicated to this topic. An observational campaign was devised with a selection of filters and exposure times tailored to maximize the possibility of detecting small companions and determining their bound orbits. Data were analyzed with suitable methods to remove cosmic ray hits and known background objects, in order to search for persistent detections of potential interesting flux sources. We found no unambiguous detections of a satellite larger than ∼ 160 m inside the entire sphere of gravitational influence. Our search confirmed the absence of bound companions larger than ∼ 30 m inside 20 primary radii. These limits are a factor of ∼ 30 smaller than the values reported so far from large ground-based telescopes using adaptive optics and from the Hubble Space Telescope.