During the meteorite aerobreaking in the Earths atmosphere the meteorite body is subject to intensive pressure. The pressure within the meteorite body can reach several megapascals (Borovička et al., 2002). Depending on the material fragility, the effect of the pressure on the survival of the body is critical. In most cases this process is responsible for fragmentation of the stony meteorites and reduces the chance of the body to reach the Earth surface.

There have been many works done on the influence of pressure on the magnetic parameters (Kapička, 1984; Kapička, 1990; Kapička, 1992). Applying those ideas on meteorite and atmosphere entry event there are coming three questions:

To answer those questions we choose the Allende meteorite as a subject of laboratory simulation. Comparing to others primitive chondritic meteorites (for example described Murchison interior sample), Allende is carrier of the relative stable single component NRM (Brecher et al., 1974).

The question is, whether this magnetization is space or terrestrial origin. Allende meteorite carries no traces of intensive terrestrial weathering. Therefore the weathering process is not expected to be responsible for the possible remagnetization. The results of different samples within the whole meteorite body points to the same level of NRM stability. That allows us to eliminate the influence of thermal shock as the remagnetizing process as well. According to those consequences an experiment has been designed to test the possibility of the pressure shock effects on the meteorite magnetization.

Experiment Procedure

The fragment of Allende meteorite had been demagnetized prior to the experiment using LDA-3 AF demagnetizer up to 100 mT to remove sample’s remanent magnetization and to test its character. However we have to notice, that the field of 100 mT was not enough to completely demagnetize Allende sample and to reach the demagnetization “noise level”.

To expose Allende sample to high pressure the apparatus located in the laboratory of the Institute of Geophysics, Academy of Sciences of the Czech Republic has been used. This instrument is designed to expose rock samples to uniaxial or hydrostatic pressure up to 120 MPa.

The sample holder is designed to measure cylindrical rock samples 1 cm high and 0.8 cm in diameter. Due to this requirement Allende sample (sized 2 mm) has been fixed in the non magnetic organic resin and worked to the required dimensions. Prior the experiment two types of resin have been tested (ChS Epoxy^® 1200 resin and Dentacryl^® resin). As exposed to the pressure the cylinders made of Epoxy^® resin showed more solid behavior with less degree of deformation. This gives more precise press transfer through the resin cylinder to the meteorite fragment.

During experiment the sample has been exposed to pressure within the terrestrial field to pressures from 2 MPa in steps of 2 MPa up to 10 MPa. The residence time under the pressure was approximately five seconds.

Experiment Results

Original NRM of Allende sample was 26 x 10^-4 Am²/kg. After 100 mT field applied it decreases to 7 x 10^-4 Am²/kg.

The sample has been then fixed into the Epoxy^® resin and worked out to desired dimensions. Before the experiment the sample has been demagnetized in 100 mT field once again in order to remove potential viscose acquisition. The magnetization of sample fixed within the resin after 100 mT field applied was 2,7 x 10^-4 Am²/kg. During the experiment sample has been exposed to uniaxial pressure up to 10 MPa. There has been slight increase in sample magnetization between 2 and 4 MPa observed. However the total increase of magnetization during the experiment has been 0.3 x 10^-4 Am²/kg to final value of 3 x 10^-4 Am²/kg only. That means that the acquired magnetization (3 x 10^-4 Am²/kg) was one order of the magnitude lower than the original NRM (26 x 10^-4 Am²/kg). The measured values are summarized in the table.

According to those results, pressure during atmospheric aero-braking seems to be not responsible for Allende remagnetization. However there are problems with the pressure transfer using organic resin. The deformation of the resin cylinder starts at the pressures around 7 MPa. There can be only estimates done on the efficiency of the pressure transfer through relatively ductile resin to the solid sample during the experiment. The Allende meteorite with its stable single component magnetization has to be the subject of the future work.