Chondrules are the millimeter-scale previously molten droplets found in chondritic meteorites. These pervasive yet enigmatic particles hint at energetic processes at work in the nascent solar system. Chondrules and chondrites are well studied and many of the details about their compositions, ages, and thermal histories are well known. Without the proper context of a formation mechanism, however, we can only imagine what chondrules may reveal about the processes at work in the early solar system. In this chapter, we explore the hypothesis that chondrules were formed by impacts between growing planetary embryos. Specifically, we focus on shock heating associated with accretionary impacts as a means for melting chondrule precursor material. Although we discuss previous work on impact origin for chondrules, much of this chapter focuses on a new incarnation of this old idea, the impact jetting model. We explore the predictions of this model and its implications for our understanding of early solar system history and meteoritics. Throughout the chapter, we discuss potential issues and uncertainties with the model while identifying avenues for further development and testing of the impact origin hypothesis.
Chondrules contain ferromagnetic minerals that may retain a record of the magnetic field environments in which they cooled. Paleomagnetic experiments on separated chondrules can potentially reveal the presence of remanent magnetization from the time of chondrule formation. The existence of such a magnetization places quantitative bounds on the frequency of interchondrule collisions, while the intensity of magnetization may be used to infer the strength of nebular magnetic fields and thereby constrain the mechanism of chondrule formation. Recent advances in laboratory instrumentation and techniques have permitted the isolation of nebular remanent magnetization in chondrules, providing the potential basis to probe the formation environments of chondrules from a range of chondrite classes.
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