Gunter Kletetschka, a research scientist from the University of Alaska Fairbanks’ (UAF) Geophysical Institute, discovered a way to locate and define meteorite impact sites that no longer have craters due to erosion. In addition to helping geologists study Earth, this discovery could teach us more about other planets in our solar system. Kletetschka says that the key to this discovery was in “the significantly 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.”

Rock Magnetization

Rocks generally have 2% to 3% natural remanent magnetization. In other words, they consist of 2% to 3% of magnetic mineral grains (magnetite or hematite or both). Studying samples collected at the Santa Fe Impact Structure in New Mexico — the eroded remains of an impact site — Kletetschka found that the rocks had less than 0.1% magnetism.  With that information, he determined that reasons for less magnetism include 1) the plasma created at the time of impact and 2) a change in behavior in the electrons in the rocks’ atoms.

Santa Fe Impact Structure

The Impact Structure in New Mexico was discovered recently in 2005. Scientists believe it’s around 1.2 billion years old. It is made up of shatter cones — rocks with fantail features and radiating fracture lines. The commonly held belief is that shatter cones form when rock is subjected to high-pressure and high-velocity shock waves, like what would occur in the case of a meteor or nuclear explosion. 

The Impact of New Findings

Kletetschka’s findings of low magnetism in the rock at impact sites will allow future researchers to narrow down the impact site even further before any shatter cones are found. This means we can better define the extent of known impact sites that no longer have craters that essentially function as a sign to “Look here.” “As soon as there is contact with that [tremendous] velocity,” he says, “there is a change of the kinetic energy into heat and vapor and plasma.” Plasma is a gas in which atoms have broken into free-floating negative electrons and positive ions.

Study Conclusions

The Earth’s magnetic field lines move through everything on the planet. As such, magnetic stability can be temporarily knocked out of rocks by shock waves, but after it passes, the magnetic stability returns. However, at the Santa Fe site, while the impact led to a change in atoms, the impact weakened the field in the surrounding areas, preventing the rocks from regaining their 2% to 2% magnetism.  Plasma also increased the rocks’ electrical conductivity as they went from vapor to molten rock, temporarily weakening or shielding the ambient magnetic field. 

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