Dr. Elizabetta Pierazzo

Research Report 2007

1. Mars Research

Dr. Pierazzo and her team continued their investigation of Mars impacts focusing on characterization of mixed targets that is how to best model targets with mixed materials which is very important for realistic impact results. Recent results suggest that the distribution of ice/water in the martian substrate is not important in the case of large impacts (producing craters >100 km in diameter) where the thermally important region driving the hydrothermal circulation, the central uplift, is made of dry rocks from the substrate. In that case, it is water presence around that region and its initial phase that may affect the development of any hydrothermal circulation.

Fig. 1. Final temperature field under a model Martian crater with diameter ~170 km. Temperatures above 600K within the central uplift result from combination of lower (and initially hotter) crustal rocks uplift and shock+deformational heating. Using terrestrial craters as analogs, we expect high fracturing and high permeability of these (initially dry) rocks. Beyond a radial distance of ~50 km (inner crater slope) ground ice should not be melted (roughly bounded by the 373K isotherm). The wettest region below the crater floor is at the bottom of the annular trough (~20 to ~50 km from crater center). After complex crater formation this annular zone is covered with impact melt and breccia.

2. Impacts and lithospheres

Dr. Pierazzo and her team continue to investigate the effect of target lithologies on the impact cratering process. The nature of the target material is a very important parameter in impact cratering, influencing every stage of the impact event, and affecting the environment locally and/or globally. Our most recent work has involved more accurate investigation of the atmospheric penetration of a Canyon Diablo type impactor, combined with three-dimensional (3D) simulations of the initial stages of the Canyon Diablo impact event to investigate target and projectile disruption and melting. The team is also investigating large terrestrial craters, such as Popigai, Vredefort and Sudbury, and the problem of distal ejecta and tektites.

3. Impact Hydrocodes Benchmarking and Validation

Dr. Pierazzo is the leader of a collective effort from the impact modeling community to uniformly compare, validate and benchmark the computer models (hydrocodes) widely used by the impact community to model planetary scale impacts and their consequences, as well as by the defense community to model large explosions and the threat to civilization due to asteroid impact. In 2007 the team has focused on a couple of validation efforts, to reproduce laboratory experiments of impact into water and aluminum, and is preparing a manuscript for publication summarizing the tests carried out so far. Codes currently used in the testing include, but are not limited to, ALE3D, AUTODYN, CTH, RAGE, SALE, SOVA, SPH, and ZEUSMP2.

Fig. 2. Left: Crater radius over time for a 7 km/s impact of an Al sphere into Al 6061-T6. Right: Crater radius versus time for a 4.64 km/s impact of a glass sphere into water.

4. Origin and Evolution of planetary biospheres

Dr. Pierazzo is continuing her research on the environmental and climatic effects of large impacts on the Earth. She has teamed with scientists from the National Center for Atmospheric Research with the intent of using WACCM, the 3D atmospheric general circulation model with interactive stratospheric chemistry, to investigate the effect on atmospheric dynamics and chemistry of a Chicxulub type impact. Over the past year, Dr. Pierazzo, supported by Dr. Tricarico, imported and tested the WACCM model to the PSI cluster. Currently, Dr. Pierazzo is testing a new module added to WACCM to simulate a heat pulse in the upper atmosphere, to investigate how the energy delivery in the atmosphere by re-entry ejecta of a large impact affects the atmospheric circulation and chemistry.

Awards and Honors

• 12/2007: AGU Fall Meeting 2007, San Francisco, CA: The effect of material properties on the impact cratering process -- INVITED PRESENTATION
• 9/2007: Workshop entitled Bridging the Gap 2: Effects of Target Properties on the Impact Cratering Process, Montreal, Canada: Environmental effects associated with impact events -- INVITED PRESENTATION

Papers

Abstracts

Pierazzo E., N. Artemieva, E. Asphaug, E. Baldwin, J. Cazamias, R. Coker, G.S. Collins, D.A. Crawford, G. Gisler, K.A. Holsapple, K.R. Housen, B. Ivanov, D.G. Korycansky, H.J. Melosh, Turtle, K. Wünnemann: The impact hydrocode benchmark and validation project: Results of validation tests, 39th LPSC (2008), Abst. #1177.

E. Pierazzo, B. Ivanov: Interaction of large impact craters with the Martian aquifer, 39th LPSC (2008), Abst. #1155.

E. Pierazzo, B. Ivanov, N. Artemieva: The effect of material properties on the impact cratering process, 2007 AGU Fall meeting. Invited.

E. Pierazzo: Environmental effects associated with impact events. Workshop entitled Bridging the Gap 2: Effects of Target Troperties on the Impact Cratering Process (2007), Abst. # 8048, Montreal, Canada. Invited.

Pierazzo E., N. Artemieva, E. Asphaug, J. Cazamias, R. Coker, G.S. Collins, D.A. Crawford, G. Gisler, K.A. Holsapple, K.R. Housen, B. Ivanov, D.G. Korycansky, H.J. Melosh, E.A. Taylor, E.P. Turtle, K. Wünnemann: The impact hydrocode benchmark and validation project: First Benchmark and validation tests, Workshop entitled Bridging the Gap 2: Effects of Target Troperties on the Impact Cratering Process (2007), Abst. #8038, Montreal, Canada.

Artemieva N.A., E. Pierazzo: The Canyon Diablo impact event: the projectile fate. 70th annual meeting of the Meteoritical Society (2007), Abst. # 5145, Tucson, AZ.

Ivanov, B.A., E. Pierazzo: Ice-rock mixture behavior in full scale impact crater modeling, 7th International Conference on Mars (2007). Abst. #3236, Pasadena, CA.

Invited Presentations:

• 12/2007: AGU Fall Meeting 2007, San Francisco, CA: The effect of material properties on the impact cratering process
• 9/2007: Workshop entitled Bridging the Gap 2: Effects of Target Properties on the Impact Cratering Process, Montreal, Canada: Environmental effects associated with impact events