Justin Wilkinson is a senior research scientist in the department of geography at Texas State University, and a senior scientist in the Earth Science and Remote Sensing Unit at the NASA-Johnson Space Center. Wilkinson's research focusses on 'unconventional' river landscapes, the end points of desert rivers, and extensive megafan depositional plains. The astronaut corps awarded him the 'Silver Snoopy' pin as Earth Observations trainer and a book on Costa Rica illustrated with astronaut photos earned him NASA's Public Service Medal. Yanni Gunnell is professor of physical geography and environmental studies at Université Lumière Lyon 2 where he studies environmental change and landscape evolution. Gunnell's research covers geomorphology, Quaternary geology, geodynamics, geoarchaeology, land-cover change, and social science. He has served as editor for nonprofit learned society journals, and as guest-editor of books and book chapters in several languages.