On December 5th, 2020, Japan’s Hayabusa2 mission successfully brought back samples it had gathered from the Near-Earth Asteroid (NEA) 162173 Ryugu.
Given that asteroids are essentially remnants from the formation of the Solar System, the analysis of these samples promises insights into the conditions prevalent at that time.
Scientists are particularly intrigued to understand how organic molecules were distributed across the Solar System shortly after its formation (around 4.6 billion years ago), potentially offering clues about the emergence of life and its possible origins.
The samples have already yielded a substantial amount of information, encompassing more than 20 amino acids, vitamin B3 (niacin), and interstellar dust.
A recent study by a team of Earth scientists from Tohoku University reveals that the Ryugu samples exhibit evidence of micrometeoroid impacts, resulting in patches of melted glass and minerals. According to their findings, these micrometeoroids likely originated from other comets, containing carbonaceous materials akin to primitive organic matter commonly found in ancient cometary dust.
Megumi Matsumoto, an assistant professor from the Earth Science Department at Tohoku University’s Graduate School of Science, led the research team. Collaborators included researchers from the Division of Earth and Planetary Sciences at Kyoto University, the CAS Center for Excellence in Deep Earth Science, the Institute of Space and Astronautical Science (ISAS), the Japan Synchrotron Radiation Research Institute (JASRI), the Japan Aerospace Exploration Agency (JAXA), and NASA’s Johnson Space Center.
Details of their findings were published in a recent issue of the journal Science Advances.
Similar to the Moon and other airless bodies, Ryugu lacks a protective atmosphere and undergoes no weathering or erosion. This ensures that craters caused by previous impacts on its surface, exposed directly to space, remain well-preserved over time.
These impacts generate intense heat, resulting in melted patches of glass, known as “melt splashes,” which solidify quickly in the vacuum of space. The impacts induce changes in the asteroid’s surface materials, disclosing information about its impact history.
Upon analyzing the Ryugu samples, Matsumoto and her colleagues identified melt splashes ranging from 5 to 20 micrometers. The composition suggests cometary sources impacting Ryugu during its near-Earth orbit.
Matsumoto stated, “Our 3D CT imaging and chemical analyses showed that the melt splashes consist mainly of silicate glasses with voids and small inclusions of spherical iron sulfides. The chemical compositions suggest that Ryugu’s hydrous silicates mixed with cometary dust.”
The analysis disclosed small carbonaceous materials with a spongy texture indicative of nano-pores, caused by the release of water vapor from hydrous silicates. This vapor was captured in the melt splashes, which also contained silicate glasses rich in magnesium and iron (Mg-Fe) and iron-nickel sulfides.
The carbonaceous materials share a texture with primitive organic matter observed in cometary dust but differ in composition, lacking nitrogen and oxygen.
Matsumoto explained, “We propose that the carbonaceous materials formed from cometary organic matter via the evaporation of volatiles, such as nitrogen and oxygen, during the impact-induced heating. This suggests that cometary matter was transported to the near-Earth region from the outer solar system. This organic matter might be the small seeds of life once delivered from space to Earth.”
Looking ahead, the team aims to examine more Ryugu samples to gain further insights into how primitive organic materials were transported to Earth billions of years ago.
Similarly, scientists at NASA’s Johnson Space Center recently completed the meticulous process of extracting samples collected by the OSIRIS-REx mission from their sample container. The analysis of these samples will unveil the composition and history of asteroid Bennu, another NEA providing crucial information on the evolution of our Solar System.