Statistics – Methodology
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..gp22a09k&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #GP22A-09
Statistics
Methodology
1517 Magnetic Anomaly Modeling, 1533 Remagnetization, 1540 Rock And Mineral Magnetism, 1594 Instruments And Techniques, 6205 Asteroids And Meteoroids
Scientific paper
In anticipation of the encounter with 443 EROS we have been evaluating the concept of S-type Asteroid magnetization which led to a reconsideration of the magnetization records of Ordinary Chondrite meteorites. The recent discovery of low magnetization for the 433 EROS asteroid allows us a step up in explaining why the magnetization might be so low. We evaluated most of the available chondritic meteorite data and found that most exceeds Eros magnetization (< 7.5 e-7 A m2kg-1) by at least two orders of magnitude (1e-4 A m2kg-1). We explore the possibility of contaminating the magnetic record by exposure to the terrestrial environment. This includes history of meteorite from the time when it enters the geomagnetic field, warms up from interplanetary space temperatures to the temperature of the Earth surface, and transport to the magnetic facility where the magnetization data is measured. Magnetic record of the Bjurbole chondrite, and by analogy perhaps all meteorites, is complicated be the fact that it contains magnetic material capable of acquiring a wide range of magnetic remanence records by warming from space temperature and magnetic conditions to 300K inside the terrestrial environment. However, there is also a significant fraction of chondrule record that contains stable remanent directions that is unlikely to be contaminated by exposure to the geomagnetic field and terrestrial temperatures. Consequently the next step is to assess the bulk effect of the space to earth transit. We also analyzed a few samples of large meteorites (ALH76009 - 23.7 kg, Allende - 17.2 kg, Canyon Diablo - 454 kg) using similar technique and methodology as the ones used on EROS. The advantage of using large meteorites is that we are able to better assess the contamination which is often experienced by small size meteorite samples. Large sample studies reveal the orientation of the bulk magnetization with respect to sample geometry and internal structure. Large samples are measured at the GSFC facility where the intensity and gradient of the magnetic field can be fully controlled. Magnetic remanence was measured in pristine state and also after demagnetization by 5 mT alternating magnetic field in near zero magnetic field. Results show that large samples have lower magnetization than small samples which points either to a larger potential for contamination of small samples or to the vector subtraction associated with randomly oriented magnetized regions within the large meteorites.
Acuña Mario Humberto
Dickinson Tamara L.
Kletetschka Gunther
Wasilewski Peter J.
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