Determine asteroid origins using sample yield analysis

Catcher chamber sample C from the second drop, captured by an optical microscope. The synthetic material appears to be in room C. The origin is under investigation, but the likely source is aluminum scraped from the spacecraft sampler horn where the projectile was fired to move material during descent. credit: JAXA


The first analysis of samples from the asteroid Ryugu brought back by the Japan Aerospace Exploration Agency’s Hayabusa2 spacecraft provides new insights into the history of Ryugu’s formation.

Laboratory analysis of 17 individual grains of samples collected by Hayabusa2 found carbon dioxide-bearing water in the iron-nickel sulfide crystal, indicating the original body formed in the outer solar system, says the research paper “The formation and evolution of the carbonaceous asteroid Ryugu: direct evidence from the samples.” returns” which appears in Science. The study was co-authored by senior scientists at the Planetary Science Institute, Deborah Domingo, Faith Vilas and Amanda Hendricks, and Tomoki Nakamura of Tohoku University in Japan is the lead author.

“The Hayabusa2 spacecraft sampled the surface twice: once on February 21, 2019, and again on July 11, 2019. The first sample was taken from the surface that was not affected by the turbulence, while the second sample was taken from the regolith extracted from the artificial collision that arose earlier. During the mission.This study examined grains from both sample sites, and provided samples that could really provide insight into the evolution of Ryugu,” said Domingo. In addition, fine-grained powder samples less than 1 millimeter from the two sample collection chambers were examined using reflective spectroscopy techniques.

The aim of these preliminary studies is to understand and characterize the history of the Ryugu formation. While the orbital data identified the presence of phyllosilicates, it was the analysis of the samples that gave us information on the detailed mineral composition and physical properties of the regolith grains,” said Domingo. The article discusses that numerical simulations based on these findings show us that the original body of Ryugu had formed after About two million years from the birth of our solar system, in the outer solar system.

The mineralogy and petrology of the samples indicate that the original body formed in the region of the early solar system where water and carbon dioxide existed as solids, more than 3 to 4 times the distance from the Sun to Earth, and possibly even beyond the orbit of Jupiter. This was followed by an inward dispersal towards the main asteroid belt, to the present orbital position of the Polana and Eulalia asteroid families, which are about 2.5 times the distance from the Sun to Earth, the Polana and Eulalia asteroid families being the possible parental families. Ryugu is based on orbital dynamic calculations of the origin of Ryugu.

Ryugu’s mother body was shattered by a widespread impact that formed either the Eulalia or Polana asteroid families, including Ryugu, which later migrated inland to its current orbit. Using the physical properties measured from the samples, the impact models show that Ryugu was formed from materials far from the impact site. The absence of shock features in mineralogy, consistent temperature with interfacial waters present in Ryugu saponite (a clay mineral) is consistent with the formation of Ryugu from fragments extracted from regions far from the impact site. The composition of Ryugu—mineral and chemical—indicates that Ryugu was formed from fragments from multiple depths within its mother body.

“Studying the Ryugu samples in the laboratory provides a great complement to other meteorite studies, as it allows us to identify this well-known meteorite. For most meteorites, the exact original body is unknown,” Hendricks said. “This then allows us to connect the dots and better understand the formation of the rubble pile, the near-Earth asteroid Ryugu.”

The minerals in the Ryugu samples in this article appear to be very similar to CI chondrites, a carbon-rich meteorite collected here on Earth. Understanding the history of Ryugu’s formation has real implications for understanding the origin of these meteorites and where their parent bodies formed in our solar system,” said Domingo.

Studies of the spectral reflectance of the samples compared to similar measurements of meteorites helped establish a connection between the Ryugu meteorites and CI. These measurements also provided the relationship between the mineralogy of the sample and remote sensing observations obtained by the camera and spectrometer aboard the Hayabusa2 spacecraft.

“Visual observations by the camera system show that the first landing site is much brighter than the second sample site, and this difference in visible reflectance between samples obtained from each site also shows,” Vilas said. Hayabusa2’s Near Infrared Spectrometer (NIRS3) observations show differences with sample measurements in the total reflectance (NIRS3 data are darker) and the clay absorption feature depth (NIRS3 spectra display a shallower feature). “This difference is partly due to the particle size range and porosity differences between the surface and the samples, which provide important information on the role of dust in the spectral properties of the asteroid regolith,” Vilas said.

The work of PSI scientists on the paper was funded by a grant to PSI from NASA’s TREX Virtual Solar System Exploration Research Institute.