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Highlighted Research Interests |
Highlight: Probing subsurface water on Mars using impact craters
Many craters on Mars have ejecta blankets that appear to have been fluidized. I have studied how the presence of ground ice alters the crater excavation process and produces a layered ejecta blanket with significant quantities of water allowing for fluidized flow. The resulting ejecta morphology may be used to infer the distribution of ground ice on Mars.
Using MOLA Digital Elevation Maps (DEMs) and impact cratering simulations, I seek to quantify the amount of water present at the time of impact. The DEMs have a resolution of better than 128 pixels/degree. Here's a comparison of a MOLA DEM and the Viking mosaic image of a 19 km diameter crater with a double layer rampart ejecta blanket. Notice how the outer ejecta layer is clearly defined in the DEM. The resolution of the MOLA data now allow for detailed comparisons between simulation results and craters on Mars.
The physical properties of planetary materials
Using shock-wave and static high-pressure techniques, I study the dynamic response (e.g., strength) and equations of state of planetary materials. My current work focuses on H2O ice and volatile mixtures.
Cratering on ice-rich materials: porosity & phase transformations
I am currently studying impact cratering on comets, Mars, and the icy outer solar system satellites and thinking about the effects of porosity on impact cratering. There has been little experimental work on the effects of porosity on cratering even though comets, some asteroids, and planetary regoliths contain significant porosity. High porosity significantly increases the amount of energy deposited by a shock wave, raising the shock temperature and producing more impact melt.
Collisional evolution of comets and planetesimals
We believe that comets contain the most pristine material in the solar system yet they experience many collisions before we observe them in the inner solar system. What are the effects of collisions in the outer solar system on a comet nucleus? The role of solid-solid phase transitions and melting of ice may play an important role in the thermal evolution of a comet.
The Shock Compression Laboratory at Harvard University
In the new shock wave lab in the Department of Earth and Planetary Sciences, the experimental program is focused on research in the planetary sciences, such as the problems outlined above. The lab capabilities include shock equation of state measurements and recovery experiments to understand physical and chemical processing by impact events. The overarching research theme is fundamental laboratory-based planetary exploration through impact experiments at the pressures and temperatures found throughout the solar system.
Mathilde is an asteroid with about 50% porosity.
Yuty crater on Mars, with a diameter of 18 km, is a classic example of a crater with the appearance of fluidized ejecta blankets.
Comet Hale-Bopp has a very large nucleus, about 40 km. Is the nucleus a reprocessed rubble pile or pristine solar system material?