Named in honor of John R. Spencer (b. 1957), an astronomer at Lowell Observatory, for his pioneering interdisciplinary work in planetary science. Spencer's research includes detailed and insightful probing into the nature and character of the Galilean satellites. In particular, he has led the field in using high-resolution, ground-based imaging of Io to provide an excellent time history of volcanism, important for bridging the gaps between spacecraft encounters. In his studies, Spencer applies a keen intuitive sense of the natural world and leaves us with a better appreciation and understanding of our solar system. Citation provided by M. W. Buie at the request of the discoverer.