 Ida 's major craters are named after caves and lava tubes on Earth . The crater Azzurra , for example , is named after a submerged cave on the island of Capri , also known as the Blue Grotto . Azzurra seems to be the most recent major impact on Ida . The ejecta from this collision is distributed discontinuously over Ida and is responsible for the large @-@ scale color and albedo variations across its surface . An exception to the crater morphology is the fresh , asymmetric Fingal , which has a sharp boundary between the floor and wall on one side . Another significant crater is Afon , which marks Ida 's prime meridian . 
