Reviewing the Impact Parameters for Meteor Crater Using Autodyn

Introduction: Meteor Crater, Arizona, is a young (50,000yr old), relatively pristine, simple crater, and is one of the most famous and most studied on the planet. Its diameter is 1.2km with a somewhat eroded rim that originally stood at 67m, but now lies at 47m [1]. Its original depth below the surface was 180m [2] but this has been partially infilled by lake bed deposits. In addition, the floor of Meteor Crater is underlain by a lens of mixed breccia ~150m thick (Figure 1). There is a wide range of parameters suggested for the iron projectile that created Meteor Crater; estimates in diameter range from 30 to 50m, while predictions for the impact velocity span from 9.4 to 20km/s [3]. We have used AUTODYN [4] to consider projectiles of varying size and velocity as part of a series of investigations to determine AUTODYN’s suitability for replicating large planetary impact events, as this is an application yet to be fully explored using this hydrocode. Model Initialisation: Grid setup. A 20x20km domain was defined, using axial symmetry. For Euler solvers a grid of 1000x1000 cells was used; comparable simulations using coupled SPH and Lagrange solvers used approximately 90,000 particles and 80,000 cells initialised with gravity. Inquiries into the most appropriate resolution of the model are ongoing. Current limitations result from the large area required to represent the target in comparison to the extremely small projectile. Projectiles must be defined by at least 10-20 particles per projectile diameter in AUTODYN, a resolution which must also be maintained for the target to ensure correct interaction between the projectile and the target. It is therefore not difficult to exceed a prohibitive number of particles if the resolution must accommodate very thin layers of different materials. The implications of this are discussed in the following subsection. Materials. The stratigraphy of the impact site is well defined, and is modelled by [5] as 9m of Moenkopi sandstone overlying 81m of Kaibab limestone, overlying 200m of Coconino Sandstone. Preliminary tests to investigate the most appropriate resolution for the model have been performed