A dark albedo feature about across has been named Olbers in honour of ORGANIZATION@1 's discoverer , but it does not appear in elevation maps as a fresh crater would , and its nature is presently unknown , perhaps an old basaltic surface .

A dark feature about NUMBER@1 km across has been named Olbers in honour of ORGANIZATION@1 's discoverer , but it does not appear in elevation maps as a fresh crater would , and its nature is presently unknown , perhaps an old basaltic surface .
