When
3:30 p.m., Sept. 14, 2010
Where
Kuiper Space Sciences 308
Melissa Morris, Research Associate at Arizona State University, is the scheduled speaker. Host: Lon Hood.
The parent bodies of the most primitive meteorites, the chondrites, formed ~4.57 billion years ago. Chondrites are remarkable for containing calcium-rich, aluminum-rich inclusions (CAIs), the oldest solids in the Solar System, whose formation has been dated to between 4567 and 4569 Ma. Also found in abundance within all chondrites (except for CI carbonaceous chondrites) are sub-millimeter- to millimeter-sized, (mostly ferromagnesian) igneous spheres, called chondrules, from which the chondrites derive their name. Chrondrules formed, at most, ~ 2-3 million years after CAIs as melt droplets that were heated to high temperatures while they were independent, free-floating objects in the early solar nebula. After they were heated, cooled, and crystallized, chondrules were incorporated into the parent bodies from which chondrites originate. Chondrules are capable of providing incredibly detailed information about conditions in the Solar System protoplanetary disk, if the process that led to their heating, melting and recrystallization could be understood. Chondrules make up to 80% of the volume of ordinary chondrites, and it is estimated that ~ 10^24 g of chondrules exist in the asteroid belt today. It is believed that the asteroid belt has been depleted by a factor of ~ 1000, indicating that there may have been ~ 10^27 g of chondrules in the primordial asteroid belt(at least a Mars mass of rock). Such a prevalence of chondrules suggests that chondrule-forming events were widespread in the solar nebula. A process that can melt 10^27 g of rock is surely a dominant process in the solar nebula disk, and must be identified. Any mechanism advanced to explain the melting of chondrules must meet the observational constraints on their formation, especially their thermal histories. In this talk, I will discuss the constraints on chondrule formation and several proposed formation mechanisms, in particular, the most widely-accepted hypothesis: that chondrules were melted in shock waves in the protoplanetary disk. I will present several alternatives as potential sources of such shock waves. Finally, I will discuss a new, interdisciplinary approach to the problem of chondrule formation.
The parent bodies of the most primitive meteorites, the chondrites, formed ~4.57 billion years ago. Chondrites are remarkable for containing calcium-rich, aluminum-rich inclusions (CAIs), the oldest solids in the Solar System, whose formation has been dated to between 4567 and 4569 Ma. Also found in abundance within all chondrites (except for CI carbonaceous chondrites) are sub-millimeter- to millimeter-sized, (mostly ferromagnesian) igneous spheres, called chondrules, from which the chondrites derive their name. Chrondrules formed, at most, ~ 2-3 million years after CAIs as melt droplets that were heated to high temperatures while they were independent, free-floating objects in the early solar nebula. After they were heated, cooled, and crystallized, chondrules were incorporated into the parent bodies from which chondrites originate. Chondrules are capable of providing incredibly detailed information about conditions in the Solar System protoplanetary disk, if the process that led to their heating, melting and recrystallization could be understood. Chondrules make up to 80% of the volume of ordinary chondrites, and it is estimated that ~ 10^24 g of chondrules exist in the asteroid belt today. It is believed that the asteroid belt has been depleted by a factor of ~ 1000, indicating that there may have been ~ 10^27 g of chondrules in the primordial asteroid belt(at least a Mars mass of rock). Such a prevalence of chondrules suggests that chondrule-forming events were widespread in the solar nebula. A process that can melt 10^27 g of rock is surely a dominant process in the solar nebula disk, and must be identified. Any mechanism advanced to explain the melting of chondrules must meet the observational constraints on their formation, especially their thermal histories. In this talk, I will discuss the constraints on chondrule formation and several proposed formation mechanisms, in particular, the most widely-accepted hypothesis: that chondrules were melted in shock waves in the protoplanetary disk. I will present several alternatives as potential sources of such shock waves. Finally, I will discuss a new, interdisciplinary approach to the problem of chondrule formation.
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