John Spencer, PhD, is an Institute Scientist at Southwest Research Institute's Department of Space Studies in Boulder, Colorado. A native of England, he obtained a Bachelor's degree in Geology from the University of Cambridge in 1978, and his PhD in Planetary Sciences from the University of Arizona in 1987. He spent four years in postdoctoral positions at the University of Hawaii before joining the staff of Lowell Observatory in Flagstaff, Arizona, in 1991. He worked there till he joined Southwest Research Institute in January 2004.
He specializes in studies of the moons of the outer planets, particularly the four large "Galilean" satellites of Jupiter, using theoretical models, Earth-based telescopes, close-up spacecraft observations, and the Hubble Space Telescope. He was responsible for temperature mapping of Jupiter's moons with the Photopolarimeter-Radiometer (PPR) instrument on the Jupiter-orbiting Galileo spacecraft, and is working on the mapping of temperatures on Saturn's moons using the Composite Infrared Spectrometer (CIRS) on the Cassini Saturn orbiter. He is particularly interested in the active volcanos and atmosphere of Jupiter's moon Io, and in the active ice eruptions of Saturn's moon Enceladus. He has also published research on Mars, asteroids, Pluto, and Neptune's moon Triton, and is a science team member on the New Horizons mission to Pluto and the Kuiper belt.
He was co-leader of the science team for NASA's 2007 study of a possible Flagship mission to Enceladus, is a member of the science team for the ongoing study of the Jupiter Europa Orbiter mission, and is leading the Satellites panel of the 2009 Planetary Decadal Survey.
His observational work has included discovery of several major volcanic eruptions on Io, the first observations of Io's volcanic plumes with the Hubble Space Telescope; discovery of sulfur gas in Io's plumes; co-discovery that Io's atmosphere is highly asymmetrical; co-discovery of ice volcanic activity on Saturn's moon Enceladus; and co-discovery of oxygen on Jupiter's moon Ganymede. His theoretical work has provided a probable explanation for the extreme albedo dichotomy of Iapetus, and has improved our understanding of nitrogen frost on Pluto and Triton, water frost on Jupiter's moons, and heat radiation from asteroids.
