Just over a year after Japan’s Hayabusa2 mission returned the first subsurface sample of an asteroid to Earth, scientists have determined that the near-Earth asteroid Ryugu is a pristine remnant from the formation of our solar system.
This was the first material to be returned to Earth from a carbon-rich asteroid. These asteroids can reveal how our cosmic corner of the universe was formed.
The organic and hydrated minerals locked within these asteroids could also shed light on the origin of the building blocks of life.
Ryugu is a dark, diamond-shaped asteroid that measures about 3,000 feet (1 kilometer) wide. Hayabusa2 collected one sample from the asteroid’s surface on February 22, 2019, then fired a copper “bullet” into the asteroid to create a 33-foot wide impact crater.
A sample was collected from this crater on July 11, 2019. Then, Hayabusa2 flew by Earth and dropped the sample off in Australia last December.
The C-type, or carbonaceous, asteroid is much darker than scientists originally thought, only reflecting about 2% of the light that hits it, according to one study published Monday in the journal Nature Astronomy.
After opening the sample, scientists were surprised to find that the spacecraft collected 5.4 grams from the asteroid – much more than the single gram they were expecting, said Toru Yada, lead study author and associate senior researcher at the Japan Aerospace Exploration Agency’s Institute of Space and Astronautical Science.
In the second study, also published Monday in Nature Astronomy, the researchers determined that Ryugu is made of clay and other hydrated minerals, with a number of carbonates and organics inside the sample.
These results are the first to be published about the Ryugu sample.
Ryugu appears similar to rare carbonaceous chondrites, primitive meteorites that are rich in organics. There are approximately 65,000 known meteorites on Earth, according to the Natural History Museum in London. Only 1,206 have been witnessed falling, and of these, only 51 are carbonaceous chondrites.
But Ryugu is darker, more porous and more fragile than expected when compared with carbonaceous chondrites. The density of the samples is also much lower from that of any other studied meteorites. Ryugu’s low density aligns with the idea that the asteroid is a little pile of rubble of fragments held together by gravity.
These samples helped the researchers confirm detections made while Hayabusa2 was near Ryugu.
“Some of these material properties are close to those of the carbonaceous chondrites that we have in our collections, while some were clearly distinct, which is quite exciting,” said Cédric Pilorget, lead author of the second study and associate professor at the Université Paris-Saclay’s Institut d’Astrophysique Spatiale in France.
“These samples, thus, constitute a uniquely precious collection, which may contribute to revisiting the paradigms of our Solar System origin and evolution.”
Samples from asteroids like Ryugu present researchers with a rare opportunity to directly study leftovers from the origin of the solar system and its planets. That’s because they haven’t been contaminated by falling through Earth’s atmosphere and landing on its surface, like meteorites.
This pristine view into the origin and evolution of organic matter represents the most primordial material available in Earth laboratories to date, the researchers said.
“As the mission team member, I felt so happy to handle and analyze the first C-type asteroid samples with my hands,” Yada said.
“This was (and still is!) an incredible experience,” said Pilorget via email. “The team work and international collaboration is really exemplary and I am really happy and proud to be part of this great mission.”
Some of the samples have been shared with other research teams and more findings about Ryugu are expected soon, Yada said.
Samples from Bennu, an asteroid that may share similarities to Ryugu, are currently en route to Earth after NASA’s OSIRIS-REx mission collected them in October 2020. The samples will return to Earth in September 2023.
“We would like to compare Ryugu samples with Bennu samples to see what is similar and what is different between them,” Yada said.
Patrick Michel, director of research at the French National Centre for Scientific Research in Paris, is an investigator for both missions. While he did not participate in this research, he regards these first results as historic “because they give the very first results of the preliminary analysis of samples from a carbonaceous asteroid.”
Samples from asteroids like these provide a different look at space rocks.
“Our collection is biased towards the strongest component of asteroids that can survive the entry in the atmosphere,” Michel said. “We need to get to asteroids and return samples to access the weakest, and probably most primitive, component of these bodies.”
Previous research has suggested that both Ryugu and Bennu are the fragments from a once much-larger celestial body that was hit by something.
“The possibility that both bodies have a common origin, or that their parent bodies come from the same region still holds,” Michel said. “We can check whether they have a common history or determine what differs and why.”