Scientist reveals cause of lost magnetism at meteorite site

Date:
November 22, 2021
Source:
University of Alaska Fairbanks
Summary:
A scientist has discovered a method for detecting and better
defining meteorite impact sites that have long lost their tell-tale
craters. The discovery could further the study of not only Earth's
geology but also that of other bodies in our solar system.



FULL STORY ==========================================================================
A University of Alaska Fairbanks scientist has discovered a method for detecting and better defining meteorite impact sites that have long lost
their tell-tale craters. The discovery could further the study of not
only Earth's geology but also that of other bodies in our solar system.


==========================================================================
The key, according to work by associate research professor Gunther
Kletetschka at the UAF Geophysical Institute, is in the greatly reduced
level of natural remanent magnetization of rock that has been subjected to
the intense forces from a meteor as it nears and then strikes the surface.

Rocks unaltered by humanmade or non-Earth forces have 2% to 3% natural
remanent magnetization, meaning they consist of that quantity of magnetic mineral grains -- usually magnetite or hematite or both. Kletetschka
found that samples collected at the Santa Fe Impact Structure in New
Mexico contained less than 0.1% magnetism.

Kletetschka determined that plasma created at the moment of impact and a
change in the behavior of electrons in the rocks' atoms are the reasons
for the minimal magnetism.

Kletetschka reported his findings in a paper published Wednesday in the
journal Scientific Reports.

The Santa Fe Impact Structure was discovered in 2005 and is estimated to
be about 1.2 billion years old. The site consists of easily recognized
shatter cones, which are rocks with fantail features and radiating
fracture lines.

Shatter cones are believed to only form when a rock is subjected to
a high- pressure, high-velocity shock wave such as from a meteor or
nuclear explosion.



========================================================================== Kletetschka's work will now 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.

"When you have an impact, it's at a tremendous velocity," Kletetschka
said.

"And as soon as there is a contact with that velocity, there is a change
of the kinetic energy into heat and vapor and plasma. A lot of people understand that there is heat, maybe some melting and evaporation, but
people don't think about plasma." Plasma is a gas in which atoms have
been broken into free-floating negative electrons and positive ions.

"We were able to detect in the rocks that a plasma was created during
the impact," he said.

Earth's magnetic field lines penetrate everything on the planet. Magnetic stability in rocks can be knocked out temporarily by a shock wave, as
they are when hitting an object with a hammer, for example. The magnetic stability in rocks returns immediately after the shock wave passes.



==========================================================================
At Santa Fe, the meteorite's impact sent a massive shock wave through
the rocks, as expected. Kletetschka found that the shock wave altered
the characteristics of atoms in the rocks by modifying the orbits of
certain electrons, leading to their loss of magnetism.

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. There was no way for the rocks
to regain their 2% to 3% magnetism even though they had the capability
to do so.

That's because of the presence of plasma in the rocks at the impact
surface and below. Presence of the plasma increased the rocks' electrical conductivity as they converted to vapor and molten rock at the leading
edge of the shock wave, temporarily weakening the ambient magnetic field.

"This plasma will shield the magnetic field away, and therefore the rock
finds only a very small field, a residue," Kletetschka said.

Kletetschka is also affiliated with Charles University in Prague,
Czech Republic. Charles University students Radana Kavkova and Hakan
Ucar assisted in the research.

========================================================================== Story Source: Materials provided by University_of_Alaska_Fairbanks. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Gunther Kletetschka, Radana Kavkova, Hakan Ucar. Plasma shielding
removes
prior magnetization record from impacted rocks near Santa Fe,
New Mexico.

Scientific Reports, 2021; 11 (1) DOI: 10.1038/s41598-021-01451-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211122135529.htm

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