The outcrop is near the sample collection site. Credit: Gunther Kletetschka.
A University of Alaska Fairbanks scientist has discovered a method for detecting and better defining meteorite impact sites that have long lost their telltale craters. The discovery could lead to further study of Earth's geology and other bodies in our solar system.
The key is in the reduced level of natural remanent magnetization of rock that has been subjected to the intense forces from a meteorite as it nears and then strikes the surface.
Natural remnant magnetization is 2% to 3% of the total magnetic content of the rock. Kletetschka found that the Santa Fe Impact Structure had less than 1% magnetism.
Kletetschka found that a change in the behavior of electrons in the rocks' atoms is the reason for the minimal magnetism.
Kletetschka's paper was published in the journal Scientific Reports.
The Santa Fe Impact Structure is about 1.2 billion years old. The site consists of shatter cones, which are rocks with fantail features. When a rock is subjected to a high-pressure, high-velocity shock wave such as from a meteorite or nuclear explosion, shatter cones are believed to only form.
Kletetschka's work will allow researchers to determine an impact site before shatter cones are discovered and to better define the extent of known impact sites that have lost their craters due to erosion.
Kletetschka said that an impact is at a tremendous speed. There is a change in the energy when there is a contact with that speed. A lot of people understand that there is heat, but they don't think about it.
The atoms in a gas are broken down into free-floating negative electrons and positive ionized atoms.
He said that they were able to detect the creation of a plasma in the rocks.
Everything on the planet has magnetic field lines. Magnetic stability in rocks can be knocked out by a shock wave, like when hitting an object with a hammer. After the shock wave passes, the magnetic stability in rocks returns.
The meteorite's impact sent a huge shock wave through the rocks. Kletetschka found that the shock wave altered the characteristics of atoms in the rocks by changing the electrons' orbits.
The modification of the atoms would allow for a quick remagnetization of the rocks, but Kletetschka also found that the meteorite impact had weakened the magnetic field in the area. Even though the rocks had the ability to regain 2% to 3% magnetism, there was no way to do it.
The rocks at the impact surface and below have the presence of plasma. The rock's electrical conductivity was increased by the presence of the plasma, which caused the rock to change into molten and vapor rock at the leading edge of the shock wave.
Kletetschka said that the rock found a small field because of the shielding of the magnetic field.
Charles University is in the Czech Republic. The students assisted in the research.
There was a prior magnetization record from impacted rocks near Santa Fe, New Mexico. The DOI is 10.1038/s41598-021-0.
Scientific reports are in the journal.
A scientist reveals the cause of lost magnetism at a meteorite site.
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