Small Near-Earth Asteroids as a Source of Meteorites

摘要

Small asteroids intersecting Earth's orbit can deliver extraterrestrial rocksto the Earth, called meteorites. This process is accompanied by a luminousphenomena in the atmosphere, called bolides or fireballs. Observations ofbolides provide pre-atmospheric orbits of meteorites, physical and chemicalproperties of small asteroids, and the flux (i.e. frequency of impacts) ofbodies at the Earth in the centimeter to decameter size range. In this chapterwe explain the processes occurring during the penetration of cosmic bodiesthrough the atmosphere and review the methods of bolide observations. Wecompile available data on the fireballs associated with 22 instrumentallyobserved meteorite falls. Among them are the heterogeneous falls Almahata Sitta(2008 TC$_3$) and Bene\v{s}ov, which revolutionized our view on the structureand composition of small asteroids, the P\v{r}\'{\i}bram-Neuschwanstein orbitalpair, carbonaceous chondrite meteorites with orbits on the asteroid-cometboundary, and the Chelyabinsk fall, which produced a damaging blast wave. Whilemost meteoroids disrupt into fragments during atmospheric flight, the Carancasmeteoroid remained nearly intact and caused a crater-forming explosion on theground.