A University of Alaska Fairbanks (UAF) scientist has discovered a method to detect and better define meteor impact sites that have long since lost their telltale craters. This discovery could deepen not only the study of the geology of the Earth, but also that of other bodies of our solar system.
The key, according to the work of Associate Research Professor Gunther Kletetschka at the UAF Geophysical Institute, lies in the greatly reduced level of natural remanent magnetization of rock that has been subjected to the intense forces of a meteor as it approaches. then hits the surface.
Rocks unaltered by man-made or unearthly forces have a natural remanent magnetization of 2-3%, meaning they are made up of that amount of magnetic mineral grains, usually magnetite or hematite or both . Kletetschka found that samples taken from the Santa Fe impact structure in New Mexico contained less than 0.1% magnetism.
Kletetschka determined that the plasma created at the time of the impact and a change in the behavior of the electrons in the atoms of the rocks are the reasons for the minimal magnetism.
Kletetschka share their findings in an article published in the journal Scientific reports.
The Santa Fe impact structure was discovered in 2005 and is estimated to be around 1.2 billion years old. The site consists of easily recognizable burst cones, which are rocks with fan-shaped features and radiating fracture lines. Burst cones are thought to only form when a rock is subjected to a high-pressure, high-velocity shock wave, such as that from a meteor or nuclear explosion.
Kletetschka’s work will now allow researchers to determine an impact site prior to the discovery of burst cones and better define the extent of known impact sites that have lost their craters due to erosion.
“When you have an impact, it’s at tremendous speed,” Kletetschka said. “And as soon as there is contact with that speed, there is a change of kinetic energy into heat, steam and plasma. Many people understand that there is heat, perhaps fusion and evaporation, but people don’t think of plasma.
Plasma is a gas in which atoms have been split into floating negative electrons and positive ions.
“We were able to detect in the rocks that a plasma had been created during the impact,” he said.
Earth’s magnetic field lines penetrate everywhere on the planet. The magnetic stability of rocks can be temporarily shaken by a shock wave, as is the case when hitting an object with a hammer, for example. The magnetic stability of the rocks returns immediately after the passage of the shock wave.
In Santa Fe, the meteorite impact sent a massive shock wave through the rocks, as expected. Kletetschka discovered that the shock wave altered the characteristics of atoms in rocks by altering the orbits of certain electrons, causing them to lose magnetism.
Altering the atoms would allow rapid remagnetization of the rocks, but Kletetschka also found that the meteorite impact had weakened the magnetic field in the region. There was no way for the rocks to regain their 2-3% magnetism, even if they had the ability.
This is because of the presence of plasma in the rocks at the impact surface and below. The presence of the plasma increased the electrical conductivity of the rocks as they converted to steam and molten rock at the leading edge of the shock wave, temporarily weakening the surrounding magnetic field.
“This plasma will shield the magnetic field and therefore the rock will only find a very small field, a residue,” Kletetschka said.
– This press release originally appeared on the University of Alaska Fairbanks website