O'Brien has continued his work on the collisional and dynamical evolution of the main-belt and near-Earth asteroid populations and of individual asteroids. He is currently working on several projects that fall under this area of research, including the study of the collisional evolution of the Trojan asteroid size distributions (w/ Alessandro Morbidelli), the collisional and dynamical evolution of the primordial asteroid belt (w/ Bill Bottke and Alessandro Morbidelli), and modeling and interpretation of the cratering records of the asteroids Itokawa and Eros (w/ Patrick Michel and members of the Hyabusa team).

Of particular interest is the work he presented at the DPS conference (and which is currently in preparation for publication). Several researchers have suggested that the the lack of small craters on the asteroids Eros and Itokawa could be due to the Yarkovsky effect (a radiation force) removing small impactors from the asteroid belt, but that scenario had not been modeled in detail. O'Brien's work showed that the Yarkovsky effect is much too weak to accomplish this, and any force or effect that was strong enough to accomplish this would lead to observable consequences in the main-belt near-Earth asteroid populations that are not seen. Thus, other processes, such as seismic shaking, are much more likely causes of the lack of small craters on those asteroids.

O'Brien has also continued his work on the thermal evolution and tectonics of icy satellites. He was involved in a project with Richard Greenberg's group to model the formation and evolution of strike-slip features on Europa using the Tekton finite-element code, the results of which were published this year.

The final major focus of his work is the numerical simulation of terrestrial planet accretion in our Solar System as well as in systems around other stars. He is working with Alessandro Morbidelli, Jonathan Lunine, Amara Graps, and several other researchers on issues related to the origin of water on the terrestrial planets in our Solar System. Numerical simulations of terrestrial planet formation in other planetary systems, coupled with models of the chemical evolution of those systems being developed by Jade Bond and Dante Lauretta at LPL, are providing insights into both the chemistry and dynamics of possible terrestrial planets in those systems. This work is a component of Jade's Ph.D. thesis.

Papers

O'Brien, D.P., A. Morbidelli and W.F. Bottke (2007). The Primordial Excitation and Clearing of the Asteroid Belt---Revisited. Icarus 191, 434-452.

Preblich, B., R. Greenberg, J. Riley and D.P. O'Brien (2007). Tidally Driven Strike-slip Displacement on Europa: Viscoelastic Modeling. Planetary and Space Science 55, 1225-1245.

Abstracts

O'Brien, D.P., D.R. Davis, S.J. Kenyon and B.C. Bromley (2007). The Collisional Evolution of Small Bodies in the Solar System. 7th Workshop on Catastrophic Disruption in the Solar System, Alicante, Spain (Invited Review).

O'Brien, D.P. and R. Greenberg (2007). The Lack of Small Craters on Eros is not due to the Yarkovsky Effect. American Astronomical Society, DPS meeting 39, Orlando, FL, abstract no. 50.06.

O'Brien, D.P., P. Michel and S. Abe (2007). Interpreting Itokawa's Cratering Record. 7th Workshop on Catastrophic Disruption in the Solar System, Alicante, Spain.

Bond, J.C., D.S. Lauretta and D.P. O'Brien (2007). Chemical Composition of Model Terrestrial Planets. Gordon Research Conference on Origins of Solar Systems, Mt. Holyoke College, South Hadley, MA.

Bond, J.C., D.S. Lauretta and D.P. O'Brien (2007). Chemical and Dynamical Modeling of Terrestrial Planet Formation. 70th Meteoritical Society Meeting, Tucson, AZ.

Lunine, J., A. Graps, D.P. O'Brien, A. Morbidelli, L. Leshin and A. Coradini (2007). Asteroidal Sources of Earth's Water Based on Dynamical Simulations. LPSC 38, abstract no. 1616.

Graps, A.L., J.I. Lunine, J. Chambers, A. Morbidelli, L.A. Leshin and D.P. O'Brien (2007). The Origin of Water on Mars. EGU General Assembly, Vienna, Austria, abstract no. 10556.