Winchcombe is a CM chondrite that fell in Gloucestershire on February 28, 2021. While some fragments were recovered within 12 hours of the fall on March 1, 2021, others took weeks to recover, with the last documented fragment collected on April 1. 2021.
A new analysis of the Winchcombe meteorite sheds light on how quickly Earth’s atmosphere affects the space rocks that fall toward Earth. The study, led by Laura Jenkins, a Ph.D. student at the University of Glasgow’s School of Geographical & Earth Sciences shows that despite the rapid recovery of the meteorites, the shards immediately formed multiple “earth phases” – salts and minerals – from their surfaces interacting with the moist area where they fell.
When a meteorite is exposed to terrestrial contaminants, the information it provides changes.
In their study, scientists examined two small pieces of Winchcombe for signs of terrestrial modifications. They examined the surfaces of the samples using transmission electron microscopy, scanning electron microscopy and Raman spectroscopy. Two samples were collected: one from the driveway fragments and the second from the fragments discovered in the sheep field.
The melt crust of samples from sheep fields was found to contain two forms of salts—sulfates of calcium and calcite. On the other hand, the samples from the driveway were found to contain halite, also known as table salt.
When meteorites melt during their ferocious entry into Earth’s atmosphere, a peculiar substance called the fusion crust forms. The scientists concluded that since the sulfates were found on the outside of the fusion crust, they most likely formed after the object was touched due to exposure to the moist conditions of the sheep field.
Halite, meanwhile, was only visible on the polished surfaces of the driveway section. Since the polishing was done after the meteorite was recovered, it was likely formed by the interaction of the rock disk with the humid laboratory air.
Jenkins said, “The Winchcombe meteorite is often described as a ‘pristine’ example of a CM chondrite meteorite, and it has already yielded remarkable insights.”
“However, what we’ve shown with this study is that there’s no such thing as a pristine meteorite — terrestrial change begins the moment it encounters Earth’s atmosphere, and we can see it in these samples that we get just a few months after impact. analysed. meteorite has landed.”
“It shows how reactive meteorites are to our atmosphere and how carefully we should account for these kinds of terrestrial changes when analyzing meteorites. If possible, meteorites should be stored in inert conditions to minimize terrestrial changes.”
“Understanding which phases are extraterrestrial and which are terrestrial in meteorites like Winchcombe will not only aid our understanding of their formation, but will also help relate meteorites that have landed on Earth to samples returned by sample return missions. A complete picture of the asteroids in our solar system and their role in the development of the earth.”
Dr. Luke Daly, a co-author of the paper, said: “We’ve always known that exposure to Earth’s atmosphere affects the surface of meteorites, but this is the first time we’ve been able to see how quickly the process can start and progress.”
“We were very lucky to be able to recover the Winchcombe meteorite so quickly thanks to the monitoring of the UKFall network and the efforts of the volunteers who helped us recover the largest pieces from the field.”
“This research shows the importance of monitoring the skies and assembling search groups as soon as possible after meteorites are spotted.”
- Laura E. Jenkins, Martin R. Lee et al. Winchcombe: An example of rapid terrestrial alteration of a CM chondrite. Meteoritics and planetary science. DOI: 10.1111/maps.13949