Illuminating the journey of a 4-billion-year-old asteroid
By examining tiny fragments from one of our nearest cosmic neighbors, scientists uncovered more about the history of our solar system.
image: Microscope image of one of the small fragments of asteroid 162173 Ryugu studied by scientists at the Advanced Photon Source. This fragment is roughly 400 microns in diameter, or about the width of six human hairs.
Credit: Image courtesy of Argonne National Laboratory
The Science
Researchers at the Advanced Photon Source (APS) joined an international effort to study tiny fragments of a nearby asteroid. The APS, a Department of Energy Office of Science light source user facility, provided a highly specialized tool called Mössbauer spectroscopy. The specks of asteroid dust were collected from asteroid 162173 Ryugu by a Japanese space mission. The researchers then sent samples to the APS for examination using bright X-ray beams. The team discovered that Ryugu began its life in the outer solar system as part of a larger asteroid more than 4 billion years ago. Since breaking off from its larger parent, Ryugu slowly made its way to its current orbit within 60,000 miles of Earth.
The Impact
These tiny asteroid fragments contained a wealth of information. Revelations about the history and chemical makeup of Ryugu opened a window to new insights about our solar system. Using the Mössbauer spectroscopy at APS, scientists determined that the asteroid was once made largely of ice, but temperature changes over millions of years changed its composition. The fragments contained elements that they carried with them across billions of miles of space, giving researchers key data on the formation of rocks at the outer reaches of the Milky Way.
Summary
The key contribution of the APS to this global effort is the special technique Mössbauer spectroscopy, which allowed the research team to determine the oxidation state of iron in the samples. These fragments are very small, ranging from 400 microns (about the width of six human hairs) to one millimeter in diameter. However, the APS X-ray beam can be focused down to 4 microns for this technique, allowing for several readings from each fragment.
These readings provided evidence that Ryugu was once part of a larger asteroid that formed at the outer reaches of the solar system. The structure of each sample was porous and fine-grained, meaning it once contained ice that melted over millions of years as the solar system warmed up. Researchers found a large concentration of pyrrhotite, an iron sulfide that is nowhere to be found in meteorites that otherwise resemble the Ryugu fragments. This result put limits on the temperature and location of Ryugu’s parent asteroid at the time it was formed. Taken together with results from dozens of other scientific teams, the APS data helped to tell the story of Ryugu and its journey through our solar system over billions of years.
Funding
The APS portion of this work was supported by the Department of Energy (DOE) Office of Science and the France and Chicago Collaborating in the Sciences (FACCTS) program administered by the University of Chicago. The research used resources at the Advanced Photon Source, a DOE Office of Science user facility operated by Argonne National Laboratory.