Date: 9/23/1996 - "Asteroids and Meteorites: Two Sides of the Same Coin"
Public Lecture (free) Presenter: Professor Michael J. Gaffey, Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York. Main Lecture Hall, Chemistry Building, 3:30 PM
Meteorites provide a very powerful probe of the conditions and processes of the earliest solar system. Their chemistry, mineralogy, oxidation state, isotopic patterns, thermal history and abundance of volatile elements and organic compounds indicate the conditions at their formation regions. However, meteorites do not themselves tell us where they originated in the early solar system. Meteorites thus provide temporal, chemical and thermal information but not spatial information. Establishing spatial locations of meteorite formation is a critical constraint for models of the formation and early evolution of the solar system. The meteorites appear to sample at least eighty separate parent bodies presumably located in the asteroid belt. The lack of correlation between the abundance of asteroid compositional types and the frequency of falls for the various meteorite types has lead to suggestions of a paradox, especially for the ordinary chondrites. However, studies over the past two decades have shown that very strong selection effects control the delivery of asteroid fragments to Earth. Relative abundances of meteorite types provide the information on these selection effects and delivery mechanisms, while the diversity of meteorite types provides constraints on the ranges of assemblages in the asteroid belt. Once the presumptive link between the abundances of meteorite and asteroid types is abandoned, it becomes clear that the plausible asteroid parent bodies can be identified for most meteorite types. Changing "plausible" to "probable" requires identification of a delivery mechanism consistent with fall frequency (and/or terestrial orbits) of the meteorite types and with the size of and location of the asteroid. Currently specific genetic links exist for ~35% of the meteorite falls, including the HED's (4 Vesta), the aubrites (Hungaria family), and the H chondrite/type IIE iron meteorites (6 Hebe). It is also clear that the known meteorites comprise a very incomplete sample of the range of materials present in the asteroid belt, with many new meteorite types awaiting discovery.
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
Meteorites provide a very powerful probe of the conditions and processes of the earliest solar system. Their chemistry, mineralogy, oxidation state, isotopic patterns, thermal history and abundance of volatile elements and organic compounds indicate the conditions at their formation regions. However, meteorites do not themselves tell us where they originated in the early solar system. Meteorites thus provide temporal, chemical and thermal information but not spatial information. Establishing spatial locations of meteorite formation is a critical constraint for models of the formation and early evolution of the solar system. The meteorites appear to sample at least eighty separate parent bodies presumably located in the asteroid belt. The lack of correlation between the abundance of asteroid compositional types and the frequency of falls for the various meteorite types has lead to suggestions of a paradox, especially for the ordinary chondrites. However, studies over the past two decades have shown that very strong selection effects control the delivery of asteroid fragments to Earth. Relative abundances of meteorite types provide the information on these selection effects and delivery mechanisms, while the diversity of meteorite types provides constraints on the ranges of assemblages in the asteroid belt. Once the presumptive link between the abundances of meteorite and asteroid types is abandoned, it becomes clear that the plausible asteroid parent bodies can be identified for most meteorite types. Changing "plausible" to "probable" requires identification of a delivery mechanism consistent with fall frequency (and/or terestrial orbits) of the meteorite types and with the size of and location of the asteroid. Currently specific genetic links exist for ~35% of the meteorite falls, including the HED's (4 Vesta), the aubrites (Hungaria family), and the H chondrite/type IIE iron meteorites (6 Hebe). It is also clear that the known meteorites comprise a very incomplete sample of the range of materials present in the asteroid belt, with many new meteorite types awaiting discovery.