* Astronomy

Title: The influence of terrestrial processes on meteorite magnetic records
Authors: Kohout, Tomas; Kletetschka, Gunther; Kobr, Miroslav; Pruner, Petr; Wasilewski, Peter J.

In early solar system history there are several electromagnetic processes (electric discharges, pressure shock waves, electric discharges and currents) capable of magnetizing the primitive solid particles condensating from the solar nebula. The record of these magnetic events is the main objective of rock magnetic laboratory studies of meteorites found on the Earth. However, terrestrial environment can affect the magneto-mineralogy, can cause changes in magnetic parameters and can overprint the primary magnetic record. The entry of a meteorite into the terrestrial atmosphere causes surface heating and pressure effects due to large initial velocity. The effect of surface heating was the subject of the study with the CM2 Murchison meteorite. Results show the remagnetised zone to be at least 6 mm thick. On CM3, Allende meteorite we studied an effect of pressure during the atmospheric entry. According to our results the pressure does not seem to be a source responsible for meteorite remagnetization. Some meteorites are found several days after the fall, some are deposited in a desert or on the Antarctic ice for thousands of years. Most of them contain visible traces of terrestrial oxidation and weathering. We used the sample of an L6 chondrite DaG 979 found in the Libya desert, sample of the iron meteorite Campo del Cielo (found in Argentina 5000 years after the fall), and sample of the H5 Zebrak meteorite (found several days after the fall) for weathering simulations. Weathering plays an important role in the meteorite terrestrial history and is capable of complete remagnetization of the meteoritic material. To document the terrestrial processes that influence meteorite magnetism we monitored changes in magnetic remanence and magnetic hysteresis parameters. Our results indicate that the terrestrial processes are capable of changing magnetic properties and can overprint the primary magnetic record. Therefore, an extreme care is required when selecting the meteorite samples for primary magnetic component study.

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