Presolar dust grains found in samples returned from asteroid Ryugu

An international team of researchers have found dust grains older than our Sun in samples returned from near-earth asteroid Ryugu by Japan's Hayabusa2 - the first mission to bring material back to Earth from a primitive asteroid.

The Japan Aerospace Exploration Agency (JAXA) launched Hayabusa2 in December 2014 to collect samples from asteroid Ryugu. The spacecraft returned to Earth with the Ryugu sample in December 2020.

Ryugu is a near-Earth object that belongs to a class of C-type (carbonaceous) asteroids that are rich in water, carbon, and organic compounds from when the solar system formed. Researchers suspect that bits of C-type asteroids that crashed into Earth as meteorites delivered the raw ingredients of life to Earth in the early solar system.

The samples returned by Japan's Hayabusa2 allow scientists to probe Ryugu's makeup with sophisticated microanalytical instruments and compare it to material found in primitive meteorites called carbonaceous chondrites that have crashed to Earth.

Led by Carnegie's Jens Barosch and Larry Nittler, the team detected all the previously known types of presolar grains including one surprise, a silicate that is easily destroyed by chemical processing that is expected to have occurred on the asteroid's parent body. It was found in a less-chemically-altered fragment that likely shielded it from such activity, according to a press release.

"The compositions and abundances of the presolar grains we found in the Ryugu samples are similar to what we've previously found in carbonaceous chondrites. This gives us a more complete picture of our Solar System's formative processes that can inform models and future experiments on Hayabusa2 samples, as well as other meteorites," explained Nittler, who undertook this work at Carnegie, but recently moved to Arizona State University.

Other Carnegie co-authors include Jianhua Wang, Conel Alexander, Richard Carlson, and George Cody. Their work is published in The Astrophysical Journal Letters.