William Lassell discovered Neptune's moon Triton in 1846 when investigating what he believed to be a ring of the blue planet. This photograph was taken in 1989 by Voyager 2, which is presently the only satellite to have passed close enough to Triton to make decent observations. Ironically, Voyager 2 also discovered that Neptune had several small icy rings that would have been impossible for Lassell to have observed.