It might seem like it's easy to spot a meteorite impact site, with craters in the Earth's surface showing where the objects finally came to a violent stop. It's not always that way.
Sometimes impact scars are healed over, hidden by layers of dirt and vegetation, or worn smooth again by the elements over a long period of time. Scientists have found a way to detect impact sites.
Think about a big chunk of space rock getting close to its final destination. As they move through the atmosphere, meteorites can enter Earth's atmosphere as fast as 72 kilometers per second (160,000 mph), but they start to slow down.
The beautiful light in the sky when a meteorite flies overhead is due to 'ablation', as layers and layers of the meteorite are destroyed by high-speed collisions with air molecule.
If a meteorite hits here, it will create shatter cones, impact craters, and other tell-tale signs.
This is a geological process with high temperatures, high pressures, and fast particle velocities. During this intense process, the impact forms a type of gas called a plasma, in which atoms are broken into electrons and positive ion.
"When you have an impact, it's at a tremendous speed," says Kletetschka.
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 team found that the magnetism of the rocks was around 10 times less than normal, and that the impact area was left with something weird.
Natural remanent magnetization is the amount of magnetism found in rocks.
The tiny grains of magnetic metals within Earth's soil aligned themselves with the planet's magnetic field as it gradually settled. The grains are trapped in the rock.
It's definitely there, but you can't tell by using a regular magnet, but it's definitely there and can be measured by geological equipment.
When a meteorite impact happens, the magnetic grains get a good blast of energy and there's a loss of magnetism.
The researchers write that the shock wave provides more energy than is needed to block the magnetic remanence within individual magnetic grains.
The rocks would go back to their original level of magnetism almost immediately after the shockwave passed. The magnetism never went back to its normal state after the team found it in the Santa Fe impact structure.
The grains were kept in their jostled state by the'magnetic shield' created by the plasma. The magnetic intensity dropped to 0.1 percent of the rock's saturation level, a 10-fold reduction from the natural level.
The mechanism where the shock wave appearance can generate magnetic shielding that allow keeping the magnetic grains in a superparamagnetic-like state shortly after the shock's exposure, and leaves the individual magnetized grains in random orientations, is supported by us.
Our data shows how an impact process can allow for a reduction of magnetic paleointensity, and also inspire a new direction of effort to study impact sites, using paleointensity reduction as a new impact proxy."
Hopefully this new discovery will mean that scientists have another tool in their belt when it comes to finding impact sites, even ones that don't have the normal signs of impact, such as shatter cones or craters.
The research has been published.
