Date: 11/27/1995 - "When an Irresistible Force Meets an Immovable Object: The Mechanics of Meteorite Impact"
Public Lecture (free) Presenter: Professor H. Jay Melosh, Department of Planetary Sciences, University of Arizona, Tucson, Arizona. Main Lecture Hall, Chemistry Building, 3:30 PM
The impact of a meteorite mass on the surface of the planet initiates a series of orderly (but rapid) events that eventually result in the production of an impact crater. A high speed impact is closely analogous to an explosion. The impact process can be roughly divided into three stages: Contact and compression, when strong shock waves couple the kinetic energy of the meteorite into a small region of the target; the excavation stage, when the shock wave expands and material surrounding the crater is set into motion; and finally the modification stage when the crater's walls collapse, central peaks and circular mountain chains arise, and huge ring-shaped faults develop around the crater cavity. Crater excavation is accompanied by the expansion of melted and vaporized material from the crater's interior, which may disperse highly shocked material globally over the target planet. Small amounts of material from near the surface may be spalled off at high speed and at the same time avoid high shock pressures, a process that may explain how the SNC meteorites were ejected from the surface of Mars. If the target planet has an atmosphere, the atmosphere may be partially stripped by the high speed vapor plume, which may explain Mars' present dearth of atmospheric gases.
Arkansas Center for Space and Planetary Sciences
202 Old Museum Building, University of Arkansas
Fayetteville, Arkansas 72701, USA
Tel. 479-575-7625 Fax. 479-575-7778 csaps@uark.edu
The impact of a meteorite mass on the surface of the planet initiates a series of orderly (but rapid) events that eventually result in the production of an impact crater. A high speed impact is closely analogous to an explosion. The impact process can be roughly divided into three stages: Contact and compression, when strong shock waves couple the kinetic energy of the meteorite into a small region of the target; the excavation stage, when the shock wave expands and material surrounding the crater is set into motion; and finally the modification stage when the crater's walls collapse, central peaks and circular mountain chains arise, and huge ring-shaped faults develop around the crater cavity. Crater excavation is accompanied by the expansion of melted and vaporized material from the crater's interior, which may disperse highly shocked material globally over the target planet. Small amounts of material from near the surface may be spalled off at high speed and at the same time avoid high shock pressures, a process that may explain how the SNC meteorites were ejected from the surface of Mars. If the target planet has an atmosphere, the atmosphere may be partially stripped by the high speed vapor plume, which may explain Mars' present dearth of atmospheric gases.