Two PSI Scientists Awarded Sagan Fellowships by NASA

Two PSI Scientists Awarded Sagan Fellowships by NASA

Rebecca WilliamsAncient riverbed floor
Ancient riverbed floor preserved as a curved ridge on the Colorado Plateau. Length of ridge is ~0.5 km and stands ~35 m above surrounding plains. This oblique aerial image was photographed by R.M.E. Williams from an altitude of ~1000 feet in October 2005.

August 31, 2006: Rebecca M. E. Williams and David P. O'Brien, Research Scientists at the Planetary Science Institute, are among the first awardees of the prestigious NASA "Carl Sagan Fellowship for Early Career Researchers." Only 12 people were selected for these fellowships in 2006.

Dr. Williams is being honored for her successful proposal to the NASA Mars Fundamental Research Program to study ancient riverbeds on Earth, exposed as elevated ridges in the United States and Australia, that may offer an explanation for similar curved raised features on Mars.

These features are preserved on the Earth when the riverbed is coated with a calcium carbonate cement or covered by lava, making a cast. The surrounding material is then lost by erosion, leaving behind the cast of the channel.

Dr. Williams will conduct field research to identify characteristics of these landforms that would allow them to be recognized from Mars orbit. In addition she will be evaluating models for estimating the flow of water through these ancient channels and then applying these models to the Martian landforms to determine how much water flowed through them for how long. This research will also give us a better understanding of when water was flowing on the surface of Mars.

David O'BrienAsteroid Collision
Asteroid collisions were an important process in shaping the early solar system. Artwork courtesy of W.K. Hartmann.

Dr. O'Brien is being honored for his successful proposal to the NASA Planetary Geology and Geophysics Program to better understand the influence of collisions and gravitational interactions on the evolution of the solar system.

This includes exploring the collisional and dynamical environment of the primordial disk of planetesimals that existed beyond Neptune in the early solar system, and the imprint that has left in the modern population of Kuiper Belt objects and comets.

Dr. O'Brien will also study the effects of large random collisions on the evolution of the Jupiter Trojan population of asteroids. These asteroids form two large clouds that lead and trail Jupiter around its orbit, trapped in gravitational resonance with the planet. This work will provide insight into the differences in population between these two clouds.

Dr. O'Brien will also be working to understand the effects of Jupiter and Saturn on the formation and evolution of the asteroid belt, Earth and the terrestrial planets.

PSI will be receiving $690,000 over the next three years for Drs.Williams and O'Brien.

Contact information: 520-620-6300

Dr. David O'Brien - obrien [at] psi. edu
Dr. Rebecca Williams - williams [at] psi. edu


The Planetary Science Institute is a nonprofit science research institute focusing on the exploration of the solar system. Our scientists are distributed in 12 states, Japan, Italy, the UK and Russia. We are headquartered in Tucson, Arizona, where PSI was founded in 1972. We are involved in numerous NASA missions, the study of Mars, asteroids, comets, interplanetary dust, the origin of the solar system, planet formation about other stars, dynamics, impact physics, and the rise of life. PSI scientists conduct field work in North America, Australia and Africa. They are also actively involved in science education and public outreach through school programs, children's books, popular science books and art.

Tucson AZ - Phoenix AZ - Angwin CA - Altadena CA - Cupertino CA - Laguna Niguel CA - Pasadena CA - San Diego CA - Washington DC - Honolulu HI - Columbia MD - Los Alamos NM - Reno NV - Spearfish SD - Houston TX - San Antonio TX - Seattle WA - Evansville WI - Wheeling WV -- London UK, Rome IT, Moscow RU, Tokyo JP