The asteroid Ryugu contains some of the most primitive materials ever studied in a lab on Earth, dating back just 5 million years after the solar system formed, according to an analysis of samples recovered by Japan’s Hayabusa2 mission.
Because it is so old, it is made of the same material that formed the planets. “Ryugu is one of the building blocks of the Earth,” team member Hisayoshi Yurimoto, a professor at Hokkaido University in Japan, told Space.com.
The Japan Aerospace Exploration Agency’s Hayabusa2 spacecraft launched in December 2014 and arrived at asteroid Ryugu in 2019. It extracted two small samples of regolith, totaling 5.4 grams, from the asteroid. These monsters then landed on earth in a capsule equipped with a parachute in December 2020.
Related: Japanese Hayabusa2 Asteroid Ryugu Monster Return Mission in Pictures
Upon their return, the samples were distributed among scientific groups, including a team led by Tetsuya Yokoyama, a professor at the Tokyo Institute of Technology. The team’s newly published results suggest that the composition of the samples best matches the solar nebula — the cloud of gas that condensed around the Sun and planets – ever found. As such, it consists of the ingredients that formed the solar system 4.5 billion years ago.
Supporting the findings previous research who also concluded that Ryugu was made of primitive material, but until now it was unknown how old it was.
Ryugu is a carbonaceous chondrite, meaning it is made of carbon-rich rock-like material. But remote observations by Hayabusa2 found some inexplicable discrepancies – including a darker surface color, greater abundance of phyllosilicate materials, and a more porous composition than expected – so lab analysis was needed to determine the asteroidthe true nature. Ryugu is somewhat like the Ivuna meteorite, which fell in Tanzania in 1938 and was loaned to Yokoyama’s team by the Natural History Museum in London for their study.
“The comparison between Ivuna and Ryugu is very helpful in revealing the characteristics of Ryugu,” Yurimoto said.
Using a range of techniques — including electron microscopy, X-ray fluorescence, inductively coupled plasma mass spectrometry and thermal ionization — the team found that the samples had formed in liquid water, at a temperature of about 81 to 117 degrees Fahrenheit (27 to 47 degrees Fahrenheit). degrees Celsius), about 5 million years after the solar system started to form.
At just 900 meters in diameter, Ryugu is too small to have generated enough heat to melt water ice. Therefore, Ryugu itself must have evolved from a larger parent body that formed only 2 million to 4 million years after the birth of the solar system. At some point, after 5 million years, a powerful collision with another asteroid Ryugu’s parental body broke apart, containing some of the fragments that made up Ryugu. This idea is supported by the presence of large boulders on the surface of Ryuguthat appear to have formed as the rubble of a giant impact.
Ryugu’s material can be dated thanks to the abundance of certain elements – hydrogen and noble gases – in the samples. They are the best match we have for the composition of the visible surface of the sun, the photospherewhich is used as a proxy for the composition of the solar nebula.
No meteoritic or asteroid material studied in a lab on Soil has once been found to be so primitive and untouched. Some meteorites, like Ivuna, may have once been so pristine. But after decades, if not centuries, on Earth — where they were exposed to atmospheric moisture and weathering and then handled by humans — their mineralogy and elemental makeup may have been compromised.
An important question that must be answered to fully explain the origin of the planets is where small bodies, such as: asteroids and comets, some of which became planetary building blocks. Their composition suggests that many of these bodies did not form in their present orbits and that in the chaotic early solar systemwith its turbulent protoplanetary disk and migrating planets, the small bodies were pushed around and away from where they formed.
If we know when Ryugu’s parent body formed and that it contained water, can we tell where the asteroid must have formed?
“This is a very difficult question,” Yurimoto said. “We don’t have a quantitative answer, but it would be beyond the snowline of the solar system, [which is] located in the orbit of Jupiter.” (The snow line is the distance from the sun where water ice could condense during the formation of the solar system†
This is just the beginning of the analysis of the samples Hayabusa took home† The next step is to use the information in those samples to determine the abundances of various elements and their isotopes in the early solar system as the planets formed. According to Yurimoto, once established, those amounts would “set a new standard for studies of the solar system.”
The findings are published in the June 9 issue of the journal Science†
Follow Keith Cooper on Twitter @21stCenturySETI. follow us on Twitter @Spacedotcom and further facebook†