Magnetic reconnection flares in the photoplanetary nebula and the possible origin of meteorite chondrules

Abstract

Many primitive meteorites are composed largely of chondrules, small once-molten beads of glassy rock. The existence of chondrules poses a basic problem for our understanding of the photoplanetary nebula inasmuch as the chondrules seem to have been melted by very short-lived, transient heating events in otherwise cool nebular sorroundings. In this paper, the possibility is investigated that meteorite chondrules formed as a result of melting of protosolar nebula dust balls by the energy released from magnetic flares in the nebula's corona. Analysis of the energy that could be released by magnetic reconnection events in nebular coronal flares shows that previously existing dust balls could be heated transiently to temperatures sufficiently high (above 1700°K) to cause the short-lived melting events that are needed to account for the existence of chondrules. The release of flare energy at rates sufficient to account for chondrule melting requires that the flares occur in the presence of magnetic fields somewhat in excess of 5 G in a low-density coronal region of the disk. Nebular magnetic fields of this strength are in accord with magnetizing fields that have been inferred from the measured remanent magnetization of primitive meteorites.