Are Asteroids Primitive?
• Ida (56 km diam.) and its moon Dactyl (1.5 km diam.)
– Colors have been “stretched” to show subtle differences
• Imaged by Galileo on its way out to Jupiter
• Presence of craters indicates great age
– Absolute age requires knowledge of cratering rate – uncertain
– Not spherical – gravity too weak to pull it into a sphere