Short Biography for John Spencer (last updated January 2022) John Spencer is an Institute Scientist at Southwest Research Institute's Department of Space Studies in Boulder, Colorado. A native of Lancashire, England, he obtained a Bachelor's degree in Geology from the University of Cambridge in 1978, and a 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, and other small outer solar system bodies, 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 worked 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. He is a science team member on the New Horizons mission to Pluto, and a deputy project scientist for its extended mission into the Kuiper belt. He coordinated the search for Kuiper Belt object (KBO) flyby targets beyond Pluto, which led to the discovery of New Horizons' next target, the small KBO Arrokoth. He also led the search by New Horizons, during Pluto approach, for potential debris hazards in the Pluto system, and led the science planning of the successful 2019 flyby of Arrokoth. On NASA's Europa Clipper mission, now under development, he is a member of the Ultraviolet Spectrometer team, and deputy PI of the Europa Thermal Emission Imaging System (E-THEMIS). He is also a co-investigator, and instrument scientist for the Long-Range Reconnaissance Imager (LORRI), on the Lucy mission to the Trojan asteroids, due to launch in late 2021. He was co-leader of the science team for NASA's 2007 study of a possible Flagship mission to Enceladus, was a member of the science team for the 2008 - 2009 studies of the Jupiter Europa Orbiter mission, and led the Satellites panel of the 2009-2011 Planetary Decadal Survey. In 2016 he won the American Geophysical Union (AGU) Whipple Award for "outstanding contributions in the field of planetary science", and in 2021 he was elected a Fellow of the AGU. 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; co-discovery of the "Pac Man" thermal anomalies on Mimas and Tethys; co-discovery of oxygen on Jupiter's moon Ganymede; and co-discovery of oxygen emissions from Callisto's atmosphere, and participation in the many discoveries made by New Horizons at Pluto and Arrokoth. 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.