Upper limits on the size of satellites of Asteroid (4) Vesta from 2007 Hubble Space Telescope observations

We imaged the region around Asteroid (4) Vesta in nine long exposures using the Wide Field Planetary Camera 2 on the Hubble Space Telescope on May 14 and 16, 2007 to conduct a deep search for satellites in support of NASA’s Dawn mission that orbited (4) Vesta in 2011–2012. Several previous search efforts have been undertaken, but no satellites were detected. Our search covered distances from 14 to 260 Vesta radii and searched to a limiting magnitude of 22.5 ± 0.4 in HST’s wide-band red filter (F702W). Our upper limit for possible satellites corresponds to a satellite just 22 ± 4 m in radius, assuming the same optical properties as Vesta. Our upper limit is ∼10 times smaller than the best limit of previous searches. In situ satellite searches by NASA’s Dawn spacecraft will probe regions closer to Vesta than our effort reported here.