A scientist from the University of Alaska Fairbanks (UAF) has discovered a method to detect and better define impact sites of meteorites that have long lost their telltale craters. The discovery could further study not only the geology of the Earth, but also that of other bodies in our solar system.
The key, according to the work of associate research professor Gunther Kletetschka at the Geophysical Institute of UAF, lies in the greatly reduced level of natural residual magnetization of the rock which has been subjected to the intense forces of a meteor while it approaches then hits the surface.
Rocks unaltered by man-made or non-terrestrial forces have a natural remanent magnetization of 2-3%, which means that they are made up of that amount 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 percent magnetism.
Kletetschka determined that the plasma created at the time of impact and a change in the behavior of electrons in rock atoms are the reasons for the minimal magnetism.
Kletetschka shared his 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 fantail characteristics and radiating fracture lines. It is believed that rupture cones only form when a rock is subjected to a high-pressure, high-speed shock wave, such as that from a meteor or a nuclear explosion.
Kletetschka’s work will now allow researchers to determine an impact site before breakage cones are discovered 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 velocity, there is a change in kinetic energy into heat, vapor and plasma. A lot of people understand that there is heat, maybe melting 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 was created during the impact,” he said.
Earth’s magnetic field lines penetrate everything on the planet. The magnetic stability of rocks can be temporarily canceled out by a shock wave, as is the case when hitting an object with a hammer, for example. Magnetic stability in 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 alters the characteristics of atoms in rocks by changing the orbits of certain electrons, leading to their loss of magnetism.
Altering the atoms would allow the rocks to re-magnetize quickly, but Kletetschka also found that the meteorite’s impact weakened the magnetic field in the area. There was no way for the rocks to regain their 2-3% magnetism even if they had the capacity.
This is because of the presence of plasma in the rocks on the impact surface and below. The presence of plasma increased the electrical conductivity of rocks as they converted to vapor and molten rock at the leading edge of the shock wave, temporarily weakening the surrounding magnetic field.
“This plasma will protect the magnetic field, and therefore the rock only finds a very small field, a residue,” Kletetschka said.
– This press release was originally posted on the University of Alaska Fairbanks website