More than 30 small meteorite impact structures have been discovered in Wyoming, ranging from 10 to 70 meters in diameter. These small structures contain shocked quartz grains, which only form as a result of an impact, but have puzzled scientists previously because they do not contain fragments of foreign rock indicating an extraterrestrial source. A clue to their origin, however, is that several of these craters are elliptical, with the axes of the ellipses pointing to a common location on the border of Wyoming and Nebraska.
Meteorite impacts typically form circular craters, regardless of their impact angle, due to the speed at which they impact Earth. However, small elliptical craters radiating from a common point are seen on other planetary bodies. The common point of these crater fields is usually a large impact crater. It is thought that, in these cases, the impacts that formed the large craters were so large that they ejected boulders of bedrock up to hundreds of kilometers from the primary impact site, generating a “secondary impact crater field.”
A study of the impact crater field in Wyoming, led by Thomas Kenkmann from the Albert Ludwig University of Freiburg, Germany, used the radial arrangement of the craters to reconstruct their impact trajectories. The researchers’ calculations showed that the primary impactor likely hit Earth approximately 280 million years ago when the supercontinent Pangea existed, forming a 60-kilometer-wide crater that has since been buried by sand and silt. This would make the primary impact site one of the largest in North America. Future research is planned to search for additional evidence of the primary impact crater. This is the first identification of a secondary crater field on Earth, an exciting find for the planetary science community. READ MORE