Dr. Bob Craddock began his career as a geologist at the Center for Earth and Planetary Studies in 1988. He combines remote sensing data, quantitative geomorphic analyses, and terrestrial field investigations to help unravel the early geologic history of Mars and to better understand the processes that have shaped the surfaces of the other planets.
Bob grew up in twelve different states and attended high schools in Michigan, Georgia, and North Carolina. He attended college at the University of Georgia where he received a BS in geology in 1985. He then attended school at Arizona State University where he worked with Drs. Ron Greeley and Phil Christensen on a variety of projects, including mapping the volcanic surface of Jupiter's moon, Io, mapping the source region of Mangala Valles, a large outflow channel on Mars, and estimating the thickness of mare deposits within Tsiolkovsky, a large impact crater on the farside of the moon. His master's thesis focused on determining the physical characteristics of surface materials within martian outflow channels from imagery and remote sensing data. This analysis indicated that diurnal temperature differences were responsible for driving winds through the channels and redistributing any fluvial deposits that were emplaced during the waning stages of channel formation. In 1999, Bob received a PhD from the University of Virginia where he worked with Dr. Alan Howard in applying quantitative modeling to characterize the surfaces of the moon and Mars. As part of his dissertation he developed a method for age-dating small geologic units on the moon using modified impact craters, which will be important for supporting future missions to the lunar surface. He also provided some of the first quantitative analyses of modified impact craters on Mars, which indicated that precipitation and surface runoff were once important processes early in that planet's history.
While at the Center for Earth and Planetary Studies Bob's investigations have focused on understanding the geologic processes that have occurred on Mars. In a series of publications he demonstrated that erosion, rather than deposition, was responsible for creating the observed populations of modified impact craters. He also provided evidence that only erosion could explain the size range and varying degrees of crater modification. His work provided some of the first evidence that rain had fallen on the surface of early Mars. Bob has also worked on characterizing and age-dating valley networks on Mars in an effort to better understand their formation processes. Working with Ross Irwin, their research has provided detailed estimates of discharge through a valley network system, supporting the idea that these features were carved by precipitation and surface runoff similar to rivers on the Earth. However, their research has also shown that valley networks are different from terrestrial drainage systems in many respects, including evidence that valley networks were only active ephemerally and that competing processes, such as impact cratering, frustrated their development.
Bob's terrestrial research interests include several analog studies that will help us to better understand the surface of Mars. In the Ka'u Desert of Hawaii he is analyzing the history of gulley formation within the Keanakako'i Formation, which is a tephra deposit emplaced during a series of explosive eruptions at Kilauea. This analysis will help us to better understand the conditions necessary to initiate runoff and erosion on the martian surface. He is also looking at how materials eroded from the Keanakako'i Formation change chemically and physically with increasing transport distances as a way of better understanding the nature of surface materials on Mars, which are similar in composition. In Australia he is working with scientists from four countries to better understand the development of floodouts and dunes in the Simpson Desert. Linear dunes, such as those seen throughout the Simpson Desert, have been found on all the terrestrial planets with an atmosphere. To date, however, it is not clear how such dunes form. Australia also offers a unique environment for better understanding and interpreting remote sensing data, which could one day help us to map the distribution of fluvial deposits on Mars.
Through a joint appointment with the Department of Space History Bob works with curators in documenting and maintaining the National Collection of manned and unmanned planetary artifacts. He has worked directly in accessioning artifacts such as the Clementine and Mars Pathfinder engineering models, and has written exhibit scripts on many artifacts such as Lunar Module 2. His book entitled Apollo 11, Artifacts from the First Lunar Landing was awarded First Prize for Educational Resources by the American Association of Museums in 2004.
Between 2003 and 2004 Bob served in the Smithsonian's Office for the Under Secretary of Science as Science Advisor. There he worked with Under Secretary David L. Evans in implementing recommendations made by the Smithsonian Science Commission and in developing a strategic plan for the future of science at the Smithsonian. In 2005 Bob was elected chair of the Smithsonian Congress of Scholars, which is an internal organization dedicated to providing communication between the Smithsonian scholarly community and central administration.
Linear dunes are the most common dune forms on Earth, and they appear on all terrestrial planets that have an atmosphere, yet scientists still do not have a clear understanding as to how they form.
Modified impact craters attest to the fact that some form of precipitation and surface runoff occurred throughout the early history of Mars. We are conducting a systematic analysis of all modified impact craters on Mars to learn more.