Micrographs of asteroid collisions may help us understand the formation of planets

False color image of impact recrystallized phosphate mineral in Chelyabinsk meteorite. Credit: Craig Walton

New methods of dating collisions between asteroids and planets throughout the history of our solar system may help scientists reconstruct when and how planets were born.

A team of researchers led by the University of Cambridge combined dating and microscopic analysis of the Chelyabinsk meteorite, which fell to Earth in 2013 and attracted attention, to more accurately constrain the timing of ancient collision events.

Their research is Communication Earth and environmentWe investigated how the minerals in the meteorite were damaged by various impacts over time. This means that we were able to identify the largest and oldest event that may have been involved in the formation of the planet.

“The impact age of meteorites is often controversial. Our research shows that multiple pieces of evidence need to be used to be more certain about the history of impacts. Department of Earth Sciences, Cambridge.

Early in the history of our solar system, planets, including Earth, were formed from large-scale collisions between asteroids and larger objects called protoplanets.

“Evidence of these effects is very old and lost on the planet, especially because the rocks on the surface are continuously recycled by plate tectonics, so the Earth’s memory is short,” said co-author Ori. Dr. Shortle said. At the Faculty of Earth Sciences and Institute of Astronomy in Cambridge.

Asteroids and their debris that falls to Earth as meteorites, in contrast, are inert, cold, much older, and faithful timekeepers of collisions.

A new study, a collaborative study between the Chinese Academy of Sciences and researchers at the Open University, documented how phosphate minerals in the Chelyabinsk meteorite were crushed to varying degrees to connect the history of collisions.

Their purpose was to support the uranium-lead dating of meteorites. It looks at the time elapsed before one isotope decays into another.

“Most primitive meteorite phosphates are great targets for dating the impact events experienced by parental meteorites,” said Uranium-lead dating at the Institute of Geological Geophysics in Beijing, Chinese Academy of Sciences. Said Dr. Senfu. Science.

Previous dating of this meteorite revealed two collision dates. One is an older, approximately 4.5 billion year old collision, and the other has occurred within the last 50 million years.

But these ages are not so clear. Just as paintings fade over time, continued collisions obscure once-clear images, creating timeless uncertainty in the scientific world and the effects recorded. Even the numbers are uncertain.

The new study arranged the collisions recorded by the Chelyabinsk meteorite in chronological order by associating the new uranium lead ages on the meteorites with the microscopic evidence of impact-induced heating found in their crystal structures. These microscopic clues accumulate in the mineral with each successive impact. That is, you can distinguish collisions, sort them in chronological order, and date them.

Their findings indicate that the minerals containing the traces of the oldest collisions were either shattered into many small crystals at high temperatures or strongly deformed at high pressures.

The team also described some mineral particles in meteorites that are destroyed with less impact at lower pressures and temperatures and record a much more recent age of less than 50 million years.They suggest that this effect probably scraped the Chelyabinsk meteorite from its host. asteroid And I hurriedly sent it to the earth.

In summary, it supports a two-step collision history. “The question for us was whether these dates were reliable. Can these effects be linked to evidence of overheating due to the effects?” Walton said. “We have shown that the mineralogical context for dating is really important.”

Scientists are particularly interested in the date of impact 4.5 billion years ago. This is probably the time when we think the Earth and Moon system was born as a result of two things. Planetary body Collide.

The Chelyabinsk meteorite belongs to the group of so-called stony meteorites, all of which contain highly crushed and redissolved material that closely matches this enormous impact.

The newly acquired dates support previous proposals that many asteroids experienced high-energy collisions 4.48-4.44 billion years ago. “The fact that all of these asteroids are recording intense melting at this point may indicate a reorganization of the solar system resulting from either the formation of the Earth and the Moon or perhaps the orbital motion of a giant planet. . “

Walton is currently planning to refine dating beyond the windows of shock that form the moon. It can tell us how our own planet was born.

Shocked Zircon finds a “one-off gift” from Mars

For more information:
Walton, CR et al, Ancient and recent collisions revealed by phosphate minerals in the Chelyabinsk meteorite, Communication Earth and environment (2022). DOI: 10.1038 / s43247-022-00373-1

Quote: A microscopic view of asteroid collisions taken from on February 23, 2022 (2022). May 23) to help you understand

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Micrographs of asteroid collisions may help us understand the formation of planets

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