Some Asteroids and Meteorites Formed Less Than 2 Million Years After Solar System’s Birth

To understand the nascent stages of our roughly 4.6-billion-year-old solar system, researchers rely on cosmic time capsules, such as asteroids and meteorites. These materials capture the chemistry of the environments in which they formed, and one of the most pristine and primitive is a class called carbonaceous chondrites. 

But some carbonaceous chondrites are rarer than others. 

Take the meteorite Ivuna, which fell in Tanzania in 1938. Its unique chemical makeup cemented it as the type specimen for a subgroup of carbonaceous chondrites, now known as Ivuna-type carbonaceous chondrites. The near-Earth asteroid Ryugu, the study subject of the asteroid sample-return mission Hayabusa-2, is also an Ivuna-type carbonaceous chondrite. This subgroup is the closest match to the sun’s chemical composition. 

“Given that the sun takes up >99% of the entire solar system, when you hold a piece of this rock in your hand, it’s like you hold the entire solar system,” said Qing-zhu Yin, a professor in the Department of Earth and Planetary Sciences at the College of Letters and Science at UC Davis.

Now, new research is reinforcing just how unique these Ivuna-type carbonaceous chondrites are. 

In a study appearing on Thursday, Sept. 10 in Science, a research team that included the Yin Lab at UC Davis used advanced geochemical dating and analysis techniques to reveal that Ryugu and Ivuna originate from celestial bodies that formed less than 2 million years after the beginning of the solar system. This coincides with a period when the solar system was forming its first generation of planetesimals, the building blocks of planets.   

What are chondrules and why do they matter? 

The research hinged on the lack of chondrules in Ivuna-type carbonaceous chondrites. These molten silicate droplets are found in most carbonaceous chondrites. 

“The logic is that carbonaceous chondrites accreted chondrules and other matrices to form their parent bodies,” said Yin, noting that radioactive dating has revealed that these bodies formed between 2.2 and 3.5 million years after the start of the solar system. “The parent bodies of Ryugu and Ivuna, on the other hand, were accreted before 2 million years.” 

“Think of these materials as being in cold storage since the formation of the solar system,” he added. “Nature delivered these samples that witnessed the earliest phases of solar system formation for us to study.” 

A better understanding of the solar system timeline

In the study, the researchers analyzed samples from both Ryugu particles and Ivuna, focusing specifically on the samples’ dolomite crystals. These crystals form during aqueous alteration, a chemical interaction catalyzed by the presence of water. When that process occurred can be determined using geochemical dating techniques. 

“The age of the dolomite formation equals the upper limit of planetesimal accretion age,” said Yin, explaining that these bodies formed less than 2 million years after the beginning of the solar system. 

“The study not only determined the dolomite formation time but also determined the temperature of aqueous alteration by oxygen isotopes, which ranged between 37 and 96 degrees Celsius,” he added. 

Yin said the study helps solidify our understanding of the early solar system’s timeline. Namely, that the parent bodies of Ryugu, Ivuna and other Ivuna-like meteorites and asteroids formed as part of the first generation of planetesimals.