Washington, DC — Microscopically large chunks of ancient material from before the birth of our Sun were found in samples returned from asteroid Ryugu by the Hayabusa2 mission, according to new work by an international team led by Jens Barosch and Larry Nittler of Carnegie and published in The Astrophysical Journal. letters
Named after a Japanese folk tale, Ryugu is a near-Earth object shaped like a horn that orbits the Sun every 16 months. Hayabusa2 was the first mission to bring material back to Earth from a primitive asteroid, providing a unique insight into the chemical makeup of the building blocks from which our Solar System was formed.
“Different types of presolar masses originated from different types of stars and stellar processes, which we can identify from their isotopic signatures,” explained Barosch. Isotopes are versions of elements with the same number of protons, but a different number of neutrons.
He added: “The opportunity to identify and study these grains in the laboratory can help us understand the astrophysical phenomena that shaped our Solar System, as well as other cosmic objects.”
Each generation of stars sows the raw material from which the next generation is born. Like a phoenix rising from the ashes, our Sun originated more than 4.5 billion years ago when a supernova explosion swept material into a pre-existing cloud of gas and dust, causing it to collapse in on itself. The remnants of this process formed a spinning disk of material around the infant Sun from which the planets and other objects coalesced, including the progenitor bodies that eventually crashed into each other and broke up to become in asteroids and meteorites.
The samples from Hayabusa2 allow scientists to investigate Ryugu’s makeup with sophisticated microanalytical instruments and compare it to material found in primitive meteorites called carbonaceous chondrites that crashed to Earth.
The team detected all types of previously known presolar grains, including a surprise, a silicate that is easily destroyed by chemical processing that is expected to have occurred in the asteroid’s parent body. It was found in a less chemically altered fragment that probably protected it from this activity.
“The compositions and abundances of the presolar grains we found in the Ryugu samples are similar to what we have previously found in carbonaceous chondrites,” explained Nittler, who carried out this work at Carnegie but recently transfer to Arizona State University. “This gives us a more complete picture of the formative processes in our Solar System that can inform future models and experiments with samples from Hayabusa2, as well as other meteorites.”
Other Carnegie co-authors include Jianhua Wang, Conel Alexander, Richard Carlson, and George Cody.
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This work has been carried out under the auspices of the Hayabusa2 Initial Analysis Team, specifically the Chemistry sub-team led by Prof. H. Yurimoto and the Macromolecules sub-team led by Prof. H. Yabuta. This work was funded in part by NASA.