John (Jack) W. Holt received the Ph.D. degree from Caltech, Pasadena, CA, USA, in 1997. He was a Post-Doctoral Scholar at Jet Propulsion Laboratory (JPL), Pasadena, CA, USA, and then spent nearly 20 years at The University of Texas at Austin, Austin, TX, USA, where he was a Research Professor at the Institute for Geophysics and the Department of Geological Sciences. He is a Professor at the Lunar and Planetary Laboratory and the Department of Geosciences, The University of Arizona (UA), Tucson, AZ, USA. He serves as the Director of the Earth Dynamics Observatory, an institute which channels UA’s excellence in planetary science and remote sensing into a downward-looking view of Earth as a planet. He studies ice in the solar system with an emphasis on Mars and Earth. He is a Co-Investigator on the SHARAD radar sounder instrument on the Mars Reconnaissance Orbiter, conducts airborne geophysical studies of Alaskan glaciers as part of NASA’s Operation IceBridge, and has worked extensively in Antarctica. He is developing new radar sounder techniques and conducting geophysical studies of terrestrial debris-covered glaciers as Mars analogs.