SEARCH FOR SATELLITES AT CERES: UPPER LIMITS OF DETECTION FROM DAWN'S FRAMING CAMERA

Hundreds of asteroids have small secondary satellites or are double, or even multiple body systems; yet Ceres doesn’t and isn’t. Dwarf planet Pluto has five satellites yet dwarf planet Ceres has none. Ground-based and space-based telescopic searches have yielded ever-decreasing limits on the size of any small secondary bodies gravitationally bound to Ceres. The Dawn project’s satellite working group conducted a satellite search during approach to Ceres searching close to the limb where previous searches could not. Images acquired for optical navigation and rotational characterization were also searched. More than 448 images were examined for evidence of moving objects gravitationally bound to Ceres during the dedicated satellite search at range of ~145,000 km from Ceres, and phase angle of 18°. No moving objects associated with Ceres were detected. The search extended down to Ceres’ limb (previous searches went to 15,000 km above the limb) and extended the upper limit for the non-detection to 30 +/- 6 and 45 m +/-9 m radius for two effective exposure times (114s and 19s respectively). Previous upper limits to detection were in the 1-2 km range from Hubble Space Telescope observations. The Dawn mission’s search reduced the detection limit by two orders of magnitude. Why some asteroids have satellites and others don’t is the subject of dynamical speculation.