According to recent research from an international team led by Carnegie's Jens Barosch and Larry Nittler and published in The Astrophysical Journal Letters, tiny grains of ancient material that predate our Sun's birth were discovered in samples returned from the asteroid Ryugu by the Hayabusa2 mission.
Hayabusa2 Brings Back Asteroid 162173 Ryugu to Earth
Ryugu, a near-Earth object that resembles a spinning top and orbits the Sun every 16 months, is named after a Japanese folktale. It provided a unique look at the chemical composition of the primitive asteroid fragments that made up the Solar System. It was the Hayabusa2 that brought back the primitive asteroid to Earth.
The Hayabusa2 spacecraft from the Japan Aerospace Exploration Agency launched in December 2014 and arrived at asteroid 162173 Ryugu in 2019. It took two tiny regolith samples from the asteroid, totaling 5.4 grams. Then, in December 2020, these samples descended to Earth in a capsule with a parachute.
Upon their return, the samples were distributed among scientific groups. In 2020, the team led by Tetsuya Yokoyama, a professor at the Tokyo Institute of Technology, published results suggesting that the composition of the samples is the closest match to the solar nebula ever found. It is made up of the ingredients that formed the solar system 4.5 billion years ago.
Although, during this time, the researchers concluded that Ryugu was made of primitive material, they did not know how old it was.
Asteroid 162173 Ryugu Particle
The team found every type of presolar grain previously known, as well as one unexpected silicate easily destroyed by chemical processing, which is anticipated to have taken place on the asteroid's parent body. It was discovered in a less chemically altered fragment, which most likely protected it from such activity.
The presolar grains' compositions and abundances in the Ryugu samples are comparable to those in carbonaceous chondrites that the researchers have previously discovered. It provides a more thorough picture of the formation processes of the Solar System, which can be used to guide models and future research on samples from Hayabusa2 and other meteorites.
The researcher said that they could identify different types of presolar grains from their isotopic signatures, which indicate that they originated from different types of stars and stellar processes.
"We find that heavy hydrogen and nitrogen abundances are consistent with an outer Solar System origin," the researchers said. "Ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk Solar System composition."
Hayabusa2 Presolar Grains Carbonaceous Chrondrites
The Hayabusa2 samples allow scientists to examine Ryugu's composition using sophisticated microanalytical instruments and compare it to material found in primitive meteorites known as carbonaceous chondrites that collided with Earth.
The researchers said they found at least two of the carbonaceous grains are presolar graphites. On the other hand, others with moderate C isotopic anomalies are most likely organic.
According to NASA, Ryugu is a carbonaceous chondrite, which is made of carbon-rich stony material. Such findings are supported by the new study as the isotopic compositions of the presolar grains discovered in Ryugu match those found in primitive meteorites. Their abundances and compositions are comparable to presolar material found in CI chondrites.
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