© US Geological SurveyBarringer crater in Arizona was formed about 50 000 years ago by an approximately 50-meter iron meteorite.
Asteroid impacts are catastrophic events that create huge craters and sometimes melt parts of Earth's berock. "Nevertheless, craters are often difficult to detect on Earth, because erosion, weathering and plate tectonics cause them to disappear over millions of years," Langenhorst explains. Therefore, minerals that undergo characteristic changes due to the force of the impact often serve as evidence of an impact. For example, quartz sand (which chemically is silicon dioxide, SiO2) is gradually transformed into glass by such an impact, with the quartz grains then being crisscrossed by microscopic lamellae. This structure can only be explored in detail under an electron microscope. It can be seen in material from the relatively recent and prominent Barringer crater in Arizona, USA, for example.
"For more than 60 years, these lamellar structures have served as an indicator of an asteroid impact, but no one knew until now how this structure was formed in the first place," Liermann says. "We have now solved this decades-old mystery."To do so, the researchers had spent years modifying and advancing techniques that allow materials to be studied under high pressure in the lab. In these experiments, samples are usually compressed between two small diamond anvils in a so-called diamond anvil cell (DAC). It allows extreme pressures - as prevalent in Earth's interior or in an asteroid impact - to be generated in a controlled manner.
Comment: Other researches have demonstrated that, rather than a planet, it's likely that these observed perturbations are due instead to our Sun's twin, also known as Nemesis: