The Winchcombe meteorite splashed into headlines on 28 February 2021, when it streaked above Gloucestershire, England, and broke apart in the atmosphere. Its largest chunk hit a driveway in the village of Winchcombe and splattered into thousands of pieces. The homeowners discovered the fragments fewer than 12 hours later, and the UK Meteor Observation Network collected the pieces for study. Early analysis revealed that it was a rare type of water-rich meteorite. And a new study reports it had an eventful past, with its parent asteroid breaking apart, then reassembling as a result of several collisions with other bodies. Laboratory analysis has also provided details about the meteorite’s birth and evolution and found new evidence that space rocks like this one may have provided Earth with water billions of years ago.

“The research results have exceeded anything I could have dreamed of,” said Luke Daly, a geologist at the University of Glasgow and first author of the new study. “Because we recovered this meteorite so quickly, everything inside it can tell a story about its journey through space, and it can help us answer one of the biggest questions in planetary science “how did Earth get its water and become a habitable planet?”

Winchcombe is a CM chondrite, one of six classes of carbonaceous chondrites. (Chondrites, which formed as dust grains came together early in the solar system’s formation, are the most common type of meteorite, but carbonaceous chondrites, which were altered by reactions with water on the surface of their parent asteroids, are rarer, accounting for just 3% of all meteorites.) Winchcombe is brecciated, so it contains bits of several rock types, each with its own history, bound together by smaller sediments.

Analysis of the meteorite and video of its descent revealed that its parent meteoroid was probably 20–30 centimetres in diameter when it hit the atmosphere, with a mass of about 13 kilograms. “The Winchcombe meteorite was so lucky to make it through our atmosphere,” Daly said. “If it had come in any faster or slower, more steeply or less steeply, it would have been completely burnt up.”

The research team’s analyses revealed that the meteorite contains eight rock types, all of which show evidence of having been altered by water. “We think Winchcombe formed in the outer solar system because it is full of water, and ice is not stable in the hot inner solar system,” Daly said. Water must have reacted with minerals on the meteorite’s parent asteroid or asteroids (it could contain pieces of several bodies) to form the secondary minerals that the analysis detected.

The team found great diversity within rock types as well, all the way down to individual grains. Some grains had been altered by water, whereas others remained pristine. “How can you have completely altered material right next to things that haven’t been altered at all? The easiest answer is that they weren’t next to each other originally,” Mitchell said. “They came together at some later point.”

Traumatic History

During its first 10 million years or so, the parent asteroid or asteroids must have undergone a series of impacts that sent debris into space. Some of the debris splashed back onto the asteroid(s) after each collision, forming the different rock types detected in the meteorite.

After this phase, the body settled in the asteroid belt, where it orbited the Sun for billions of years. An impact about 300,000 years ago blasted off the chunk that hit Earth.

“Winchcombe’s history seems to be quite a traumatic sequence of events,” Daly said, “from formation and accretion of dust, ice, and gas, melting those ices, being fundamentally changed by fluids, breaking apart at the grain scale, reforming potentially several times, then being smashed apart again and reaccreting to form the breccia before being launched off its asteroid on a collision course with the Earth.”

In addition to revealing the asteroid’s history, the lab works also supported the suggestion that CM and other carbonaceous chondrites supplied young Earth with water and organic compounds. Daly said that the idea has been hard to assess because CM chondrites are delicate and made of materials that quickly soak up terrestrial water.

“It wasn’t clear if the water in CMs looked like the Earth because they delivered Earth’s water or if they looked like Earth because Earth’s water had gotten inside the meteorite,” Daly said. Because Winchcombe was recovered so quickly, before any rain could fall, there is no question about the source of its water. “It is still a close match to Earth’s water, suggesting that the majority of Earth’s oceans may have arrived on the backs of water-rich asteroids like Winchcombe.”

Edited from an article by Science writer Damond Benningfield. If enjoy articles like this one, drop me an email