Meteorites rapidly turn out to be contaminated after they attain Earth

On Earth, geologists study rocks to better understand the history of our planet. In contrast, planetary geologists study meteorites to better understand the history of our solar system. While these space rocks offer quite the spectacle as they enter our atmosphere at high speeds, they also offer insight into the formation and evolution of the solar system and the planetary bodies that surround it. But what happens when a meteorite crosses our dense atmosphere and lands on Earth? Will it remain in its pristine state for scientists to study? How soon should we contain the meteorite before the many geological processes that make up our planet contaminate the sample? How does this contamination affect the study of the meteorite?

These are questions a team of researchers from the University of Glasgow in the United Kingdom (UK) hopes to answer in a recent study as they study the Winchcombe meteorite, which landed in the UK in early 2021 with a known total weight of 602 grams (21.2 ounces). What makes the Winchcombe meteorite unique is that some of the fragments were collected and sealed within hours of being shot through our atmosphere, helping to preserve the meteorite for scientific study. However, even this rapid containment may not prevent contamination, as the researchers tried to find out.

“Analysis of meteorites can provide insight into the asteroids they came from and how they formed,” said Laura Jenkins, a PhD student at the Glasgow School of Geographical and Earth Sciences and lead author of the study. “Winchcombe and other meteorites like this one contain extraterrestrial water and organic matter, and the asteroids that deliver them may be responsible for delivering water to Earth and giving it enough water to form its signature oceans.” However, when a meteorite is exposed to terrestrial pollutants, particularly moisture and oxygen, it undergoes changes that affect the information it provides.”

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For the study, the researchers used Raman spectroscopy, transmission electron microscopy, and scanning electron microscopy to analyze two polished samples of the Winchcombe meteorite for so-called “terrestrial phases,” or the evolution of minerals and salts as the meteorite fragments interacted with Earth’s humid environment at the landing. One sample was taken from a home garden lawn on March 2, 2021 and the other sample was taken from a sheep pasture on March 6, 2021.

The researchers identified halite in the March 2 driveway sample and a combination of calcite and calcium sulfates in the March 6 sheep pasture sample. The calcite veins cut through the meteorite’s fusion crust, the molten material resulting from heated entry into Earth’s atmosphere, suggesting that calcite veins formed after the crust, meaning it happened after the meteorite landed.

The halite was found on the surface of the polished section and the calcium sulphates were found at the edges of the sample and included anhydrite, gypsum and bassanite. The team hypothesizes that the halite formed from the humidity of the lab over a period of months, while the calcite and calcium sulfates likely formed from the wet sheep field environment.

Learn more about the Winchcombe Meteorite and how it was discovered!

“The Winchcombe meteorite is often described as a ‘pristine’ example of a CM chondrite meteorite, and it has already provided remarkable insights,” Jenkins said. “What we have shown with this study, however, is that there really is no such thing as a pristine meteorite — the terrestrial change begins the moment it hits Earth’s atmosphere, and we can see it in these samples, which we only have a few.” Months later analyzed have landed meteorite.

“It shows how reactive meteorites are to our atmosphere and how careful we need to be to make sure we account for these types of terrestrial changes when analyzing meteorites,” Jenkins continued. “To minimize terrestrial changes, meteorites should be stored under inert conditions whenever possible. Understanding which phases in meteorites like Winchcombe are extraterrestrial and which are terrestrial will not only help in our understanding of their formation, but also help relate meteorites that landed on Earth to samples brought back by sample-return missions became. A more complete picture of the asteroids in our solar system and their role in Earth evolution can be constructed.”

The researchers stress the importance of storing quickly recovered samples in an inert atmosphere, or an atmosphere devoid of oxygen and carbon dioxide, which are often responsible for the formation of the “terrestrial phases” in meteorites. They used the Hayabusa2 and OSIRIS-REx missions as examples that pristine samples are being returned to Earth and that sample return missions are important for scientists to better understand our solar system. The researchers concluded by stating that a better understanding of meteorite weathering will help improve sample storage protocols, along with comparing such samples to earth-altered samples.

History of the Winchcombe Meteorite

Learn more about the Winchcombe meteorite a year after it landed and what it teaches us!

Just before 10:00 p.m. on the evening of February 28, 2021, a small meteorite broke apart over the English county of Gloucestershire, traveling at approximately 14 kilometers per second (8.7 miles per hour), and briefly appeared as a green fireball, the was observed by over 1000 people. The next morning, the Wilcock family, who lived in the small English town of Winchcombe, found a pile of powder and dark rocks in their driveway and a small dent in the driveway’s asphalt. While hearing the sonic boom the night before, they chose not to investigate it.

After collecting the fragments from their driveway, the family contacted the UK Meteor Observation Network (UKMON) and spent the following two days collecting powder and rocks from their driveway and front lawn. In the weeks that followed, hundreds of fragments were recovered, spanning an area from the neighbor’s driveway to several towns and the surrounding countryside. When all the fragments were collected, the total known weight was 602 grams (21.2 ounces), and this meteorite was henceforth named the Winchcombe meteorite, after the town where it landed.

What new discoveries will we make about meteorites and how the Earth is changing its composition in the years and decades to come? Only time will tell, and that’s why we know science!

As always, keep doing science and keep looking up!

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