Program and Abstract Volume LPI Contribution No. 1649 Workshop on the Early Solar System Impact Bombardment II February 1–3, 2012 • Houston, Texas Sponsors National Aeronautics and Space Administration Universities Space Research Association Lunar and Planetary Institute NASA Lunar Science Institute Conveners David A. Kring Center for Lunar Science and Exploration Lunar and Planetary Institute William F. Bottke Center for Lunar Origin and Evolution Southwest Research institute Scientific Organizing Committee Robin Canup Southwest Research Institute Gareth Collins Imperial College London James Head Brown University Alessandro Morbidelli Observatoire de la Cote d’Azur (France) Marc Norman Australian National University Richard Walker University of Maryland Lunar and Planetary Institute 3600 Bay Area Boulevard Houston TX 77058-1113 LPI Contribution No. 1649 Compiled in 2012 by Meeting and Publication Services Lunar and Planetary Institute USRA Houston 3600 Bay Area Boulevard, Houston TX 77058-1113 The Lunar and Planetary Institute is operated by the Universities Space Research Association under a cooperative agreement with the Science Mission Directorate of the National Aeronautics and Space Administration. Any opinions, findings, and conclusions or recommendations expressed in this volume are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration. Material in this volume may be copied without restraint for library, abstract service, education, or personal research purposes; however, republication of any paper or portion thereof requires the written permission of the authors as well as the appropriate acknowledgment of this publication. Abstracts in this volume may be cited as Author A. B. (2012) Title of abstract. In Workshop on the Early Solar System Bombardment II, p. XX. LPI Contribution No. 1649, Lunar and Planetary Institute, Houston. ISSN No. 0161-5297 Preface This volume contains abstracts that have been accepted for presentation at the Workshop on the Early Solar System Bombardment II, February 1–3, 2012, Houston, Texas. Administration and publications support for this meeting were provided by the staff of the Meeting and Publication Services Department at the Lunar and Planetary Institute. Early Solar System Impact Bombardment II v Contents Program ...................................................................................................................................................................... viii Modeling of Impact-Induced Age Resetting and Partial Pb-Loss in Zircon Grains O. Abramov, D. A. Kring, and S. J. Mojzsis .................................................................................................... 1 A Search for Evidence of Extraterrestrial Impacts in Jack Hills Zircons E. Bell, S. Abbott, and M. Harrison ................................................................................................................. 3 LHB Evidence on Asteroids D. D. Bogard ................................................................................................................................................... 4 The Great Archean Bombardment W. F. Bottke, D. Vokrouhlicky, D. Minton, D. Nesvorny, A. Morbidelli, R. Brasser, and B. Simonson ........................................................................................................................... 6 The Vestal Cataclysm B. A. Cohen ..................................................................................................................................................... 8 3.9 Billion Years Ago and the Asteroid Belt C. M. Corrigan, B. A. Cohen, K. Hodges, and N. L. Lunning ....................................................................... 10 Are Apollo Zircons Witness to a Lunar Cataclysm? C. A. Crow, K. D. McKeegan, J. D. Gilmour, S. A. Crowther, and D. J. Taylor .......................................... 12 LHB was Caused by Mars-Crossers, and It Was Not All that Heavy M. Cuk ........................................................................................................................................................... 14 Resonances and the Angular Momentum of the Earth-Moon System M. Cuk and S. T. Stewart ............................................................................................................................... 15 Planetary Atmospheres During an Enhanced Bombardment D. de Niem, E. Kührt, A. Morbidelli, and U. Motschmann ........................................................................... 17 Stratigraphy, Sequence, and Crater Populations of Lunar Impact Basins from Lunar Orbiter Laser Altimeter (LOLA) Data: Implications for the Late Heavy Bombardment C. I. Fassett, J. W. Head, S. J. Kadish, E. Mazarico, G. A. Neumann, D. E. Smith, and M. T. Zuber ........................................................................................................................ 18 Improving the Inventory of Large Lunar Basins: Using LOLA Data to Test Previous Candidates and Search for New Ones H. V. Frey, H. M. Meyer, and G. C. Romine ................................................................................................. 20 The Heavy Bombardment of the Moon J. P. Fritz and V. A. S. M. Fernandes ............................................................................................................ 22 187Os/188Os and Highly Siderophile Element Characteristics of Apollo 16 and 17 Impact-Melt Breccias M. G. Galenas, J. G. Liu, and R. J. Walker ................................................................................................... 24 The Impact Cratering Record for Clues on the Rate of Collisions and Provenance S. Goderis, J. Belza, and Ph. Claeys ............................................................................................................. 26 vi LPI Contribution No. 1649 Empirical Studies of Lunar Bombardment Around 3.6–4 Gy Ago W. K. Hartmann ............................................................................................................................................ 28 Early Thermal Events in the HED Parent Body (4 Vesta) Recorded in Zircon U-Th-Pb Depth Profiles from Millbillillie Brecciated Eucrite M. D. Hopkins and S. J. Mojzsis.................................................................................................................... 30 New Estimates for the Number of Large Impacts Throughout Earth’s History B. C. Johnson and H. J. Melosh .................................................................................................................... 32 Direct Detection of Projectile Relics on the Moon K. H. Joy, M. E. Zolensky, D. K. Ross, D. S. McKay, and D. A. Kring ......................................................... 34 The Collapse of Super-Isostasy: The Thermal Evolution of Large Lunar Impact Basins and a Volcanic Intrusion Model for Lunar Mascon Gravity Anomalies W. S. Kiefer, P. J. McGovern, R. W. K. Potter, G. S. Collins, and D. A. Kring ............................................ 36 Preliminary Results on the Evolution of Small Crater Populations on the Moon M. R. Kirchoff, K. M. Sherman, and C. R. Chapman .................................................................................... 38 Search for a Geochemical Record of the Late Heavy Bombardment on Earth C. Koeberl ..................................................................................................................................................... 40 New Insights to Early Bombardment Processes from Accretion Through the Basin-Forming Epoch D. A. Kring .................................................................................................................................................... 41 Spitzer Evidence for a Late Heavy Bombardment and the Formation of Urelites in η Corvi at ~1 Gyr C. M. Lisse, C. H. Chen, M. C. Wyatt, A. Morlok, P. Thebault, M. Sitko, D. M. Watson, P. Manoj, P. Sheehan, and T. M. Currie ............................................................................... 43 Two Populations of Early Lunar Impactors as Recorded in Its Ancient Crater Populations S. Marchi, W. F. Bottke, D. A. Kring, and A. Morbidelli .............................................................................. 45 Numerical Modeling of the Caloris Basin E. Martellato, J. Benkhoff, L. Colangeli, B. Foing, and S. Marchi ............................................................... 47 The Early Bombardment History of Mars Revealed in Ancient Megabasins D. A. Minton, W. F. Bottke, H. V. Frey, R. J. Lillis, J. H. Roberts, and S. T. Stewart ................................... 49 Polar Wander on Ganymede: A Possible Solution to the Apex-Antapex Cratering Conundrum P. S. Mohit, B. T. Greenhagen, and W. B. McKinnon ................................................................................... 51 The Sawtimeline of the First Billon Year of Lunar Bombardment A. Morbidelli, S. Marchi, and W. F. Bottke ................................................................................................... 53 On the History of Early Meteoritic Bombardment of the Moon: Did the Lunar Terminal Cataclysm Occur? G. Neukum, A. T. Basilevsky, T. Kneissl, G. G. Michael, and B. A. Ivanov .................................................. 55 Petrology of the Impact Melt Clasts in 60016, Ancient Regolith Breccia T. Niihara, L. Schaffer, and D. A. Kring ....................................................................................................... 57 Large Impacts at 4.2 Ga