Newswise – A year ago, scientists got their first glimpse of material collected from nearby asteroid 162173 Ryugu. Now the results of those studies have been revealed, and they shed light on the history of our solar system and the long journey of this cosmic wanderer.
In its closest orbit, asteroid 162173 Ryugu is only about 60,000 miles from Earth. It’s only a quarter of the distance to the moon. But according to findings recently published by an international team of scientists, this piece of rock began its cosmic journey more than 4 billion years ago, and billions of miles away, in the outer part of our solar system. He traveled us through space, taking in the history of this corner of the universe in the process.
These revelations are only part of the results of a worldwide effort to study samples from the surface of Ryugu. These asteroid dust grains were carefully collected and brought back to Earth by Hayabusa 2, a mission operated by the Japanese space agency JAXA, then sent to institutions around the world. Scientists have subjected these tiny fragments to dozens of experiments to unlock their secrets, determine what they are made of and how the asteroid from which they came could have formed.
“For planetary scientists, this is first-degree information directly from the solar system, and therefore invaluable.” —Esen Ercan Alp, Argonne Distinguished Fellow
The resulting article, recently published in Science, includes authors from more than 100 institutions in 11 countries. Among them is the US Department of Energy’s (DOE) Argonne National Laboratory, which houses the Advanced Photon Source (APS), a user facility of the DOE Office of Science. APS generates ultra-bright X-ray beams that can be used to determine the chemical and structural composition of samples atom by atom.
Argonne Fellow Emeritus Esen Ercan Alp led the Argonne research team, which includes physicist and group leader Jiyong Zhao and physicist Michael Hu, and beamline scientist Barbara Lavina of Argonne and from the University of Chicago. All are co-authors of the article.
Alp and his team worked for years to be included in this study. APS’ main contribution, Alp said, is a particular X-ray technique he and his team have specialized in. It’s called Mössbauer spectroscopy – named after German physicist Rudolf Mössbauer – and it’s very sensitive to tiny changes in sample chemistry. This technique allowed Alp and his team to determine the chemical composition of these fragments particle by particle.
What they and their international colleagues found was surprising, Alp said.
“There is enough evidence that Ryugu started in the outer solar system,” he said. “Asteroids found in the far reaches of the solar system would have different characteristics than those found closer to the sun.”
The APS, Alp said, found several pieces of evidence to support this hypothesis. For one thing, the grains that make up the asteroid are much finer than you would expect if it had formed at higher temperatures. On the other hand, the structure of the fragments is porous, which means that it once contained water and ice. Lower temperatures and ice are much more common in the outer solar system, Alp said.
Ryugu fragments are very small – ranging from 400 microns, the size of six human hairs, to 1 millimeter in diameter. But the X-ray beam used on the 3-ID-B beamline can be focused down to 15 microns. The team was able to perform several measurements on each of the fragments. They found the same fine-grained porous structure in all the samples.
Using the finely tuned spectroscopy capabilities of the APS, the team was able to measure the amount of oxidation the samples had undergone. This was particularly interesting since the fragments themselves had never been exposed to oxygen – they were delivered in vacuum-sealed containers, undamaged after their journey through space.
While the APS team found a chemical composition similar to meteorites that hit Earth – specifically a group of them called CI chondrites, of which only nine are known to exist on the planet – they discovered something that sets the fragments of Ryugu.
Spectroscopy measurements revealed a large amount of pyrrhotite, an iron sulfide not found in the dozen or so meteorite samples the team also studied, courtesy of French collaborators Mathieu Roskoz (Musée national d’histoire naturelle ) and Pierre Beck (Grenoble Alpes University) . This result also helps scientists limit the temperature and location of Ryugu’s parent asteroid at the time of its formation.
“Our results and those of other teams show that these asteroid samples are different from meteorites, in particular because the meteorites have gone through fiery atmospheric entry, weathering and especially oxidation on Earth” , Hu said. “It’s exciting because it’s a completely different type of sample, far out in the solar system.”
With all the data combined, the document presents the multi-billion year history of 162173 Ryugu. It was once part of a much larger asteroid that formed about 2 million years after the solar system, about 4.5 billion years ago. It was made of many different materials, including water and carbon dioxide ice, and over the next three million years the ice melted. This led to a hydrated interior and a drier surface.
About a billion years ago, another piece of space rock collided with this asteroid, shattering it and sending debris flying, and some of those fragments coalesced into the asteroid Ryugu we know today. today.
“For planetary scientists, this is first-degree information straight from the solar system, and so it’s invaluable,” Alp said.
The Argonne team is preparing their own article, detailing their X-ray techniques and results. But being part of such a large multinational scientific effort was exciting, they said, and they look forward to being part of future experiments like this.
“It was an exciting and challenging experience for us to be part of such a well-coordinated international research project.” Zhao said. “With an APS upgrade underway that will provide even brighter X-ray beams, we plan to study more material like this from distant asteroids and planets.”
This project was funded in part by a grant from France and Chicago Collaborating in the Sciences (FACCTS), administered by the University of Chicago.
About the Advanced Photon Source
The U.S. Department of Energy Office of Science’s Advanced Photon Source (APS) at Argonne National Laboratory is one of the most productive x-ray light source facilities in the world. APS provides high-luminosity X-ray beams to a diverse community of researchers in materials science, chemistry, condensed matter physics, life and environmental sciences, and applied research. These X-rays are perfectly suited to the exploration of materials and biological structures; elementary distribution; chemical, magnetic, electronic states; and a wide range of technologically important engineering systems, from batteries to fuel injectors, all of which are the foundations of our country’s economic, technological and physical well-being. Each year, more than 5,000 researchers use APS to produce more than 2,000 publications detailing impactful discoveries and solving more vital biological protein structures than users of any other X-ray light source research facility. Scientists and APS engineers are innovating in technology that is central to advancing accelerator and light source operations. This includes insertion devices that produce the extremely bright X-rays that are prized by researchers, lenses that focus X-rays down to a few nanometers, instrumentation that maximizes how X-rays interact with samples studied and the software that gathers and manages the massive amount of data resulting from discovery research at APS.
This research utilized resources from the Advanced Photon Source, a United States DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02- 06CH11357.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts cutting-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state, and municipal agencies to help them solve their specific problems, advance American scientific leadership, and prepare the nation for a better future. With employees in more than 60 countries, Argonne is managed by UChicago Argonne, LLC for the US Department of Energy’s Office of Science.
U.S. Department of Energy Office of Science is the largest supporter of basic physical science research in the United States and strives to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.