Astromaterials Science Research Group|ISAS

Research activities


The objective of the Hayabusa2 Mission (Scientific Significance)

It is believed that the key to understanding how Earth's oceans originated, how organic matter, the source of life, was delivered, how Earth's rocks incorporated water and organic matter, and the evolutionary history they have undergone lies in C-type asteroids. By obtaining information about the terrain, material, and internal structure of C-type asteroids and returning samples (fragments of the asteroid) from multiple locations to Earth, we can use the latest analytical equipment on the ground to investigate the formation history of C-type asteroids and the characteristics of water and organic matter believed to be present on these celestial bodies, as well as their relationship to Earth's water and organic matter. The analysis of the returned samples will clarify where in the solar system water and organic matter were formed, to what extent they evolved on the asteroid, whether such water and organic matter were transported to Earth, and whether they could have been the origin of Earth's water and organic matter.

Asteroid Ryugu

Ryugu is an asteroid that was discovered by the Lincoln Laboratory in 1999. It was known from observations with terrestrial telescopes to be a C-type asteroid. Classified as a near-Earth asteroid with an orbit close to Earth, it is one of the asteroids that can be reached by a spacecraft with minimal energy (fuel) expenditure. For its next sample-return mission following "Hayabusa," JAXA selected a C-type asteroid, different from the S-type asteroid (the type of asteroid Itokawa explored by Hayabusa), and asteroid 1999JU3 (its name at the time) was chosen as the exploration target for "Hayabusa2." Until the close-up investigation by Hayabusa2, only its orbit, approximate size (about 1 km), and rotation period (about 7.6 hours) were known.

Scientific Observation Instruments Aboard Hayabusa2

  • ONC (Optical Navigation Camera)

    Consisting of three cameras (a telephoto and two wide-angle cameras), it performs scientific observations and navigation (navigation) of the spacecraft.

  • NIRS3 (Near InfraRed Spectrometer)

    This instrument observes the infrared reflection from the asteroid and investigates the distribution of hydrated minerals. The '3' in NIRS3 is named after the wavelength of 3 microns in the infrared spectrum.

  • TIR (Thermal Infrared Imager)

    A device that performs asteroid thermography, imaging thermal infrared radiation in the wavelength range of 8-12µm in two dimensions. The asteroid's surface temperature varies diurnally (daily changes), increasing during the day when illuminated by the sun and decreasing at night. The diurnal variation in surface temperature is greater for fine-grained, porous rocks like sand and smaller for denser rocks. Imaging the asteroid's thermal radiation allows for the investigation of the asteroid's physical surface state.

  • LIDAR (LIght Detection And Ranging)

    Measures the distance between the spacecraft and the asteroid's surface. It also collects scientific data on the asteroid's terrain, gravity, and surface reflectance (albedo). The measurement range is from tens of meters to tens of kilometers.

  • SMP (Sampler)

    Collects samples from the asteroid's surface. Its basic design is the same as that of Hayabusa, where a small bullet is fired inside a cylindrical horn the moment its tip touches the asteroid's surface, causing the samples ejected from the surface to rise to the top of the horn and into the storage container (catcher).

Hayabusa2 Mission Chronology

December 3, 2014 Launched by the H-IIA Rocket No. 26.
December 3, 2015 Performed an Earth swing-by for acceleration.
June 27, 2018 Arrived at Ryugu (altitude 20km).
September 21, 2018 Operation of MINERVA-II1 separation.
October 3, 2018 Operation of MASCOT separation.
February 22, 2019 Touchdown on asteroid Ryugu.
April 5, 2019 The impactor created the world's first artificial crater on an asteroid.
July 11, 2019 A second touchdown was conducted, and samples of subsurface material were collected.
November 13, 2019 Departure from Ryugu.
December 5-6, 2020 Separation of the re-entry capsule.
The re-entry capsule re-entered the Earth's atmosphere and was recovered in Woomera, Australia.

Results of the Close-Range Exploration

After arriving at Ryugu, Hayabusa2 used its onboard scientific observation instruments to measure the asteroid's size, shape, and gravity precisely, as well as to conduct a survey of surface materials. The following findings were made:

  • Ryugu has a shape resembling a top with an upper and lower part stacked, with an average radius of about 450 meters.
  • Estimated weight of 4.50×10¹¹ kg.
  • Bulk density (average for the entire asteroid Ryugu) is 1.19±0.02 g/cm3, with a porosity rate of 50-60% (Watanabe et al., 2019).
    *Note: The bulk density of Ryugu particles derived from initial descriptions of the returned samples is 1.79±0.31 g/cm3. The average porosity rate is 26-31%. The grain density is estimated to be 2.59 g/cm3 (Nakamura et al., 2022) or based on the assumption of 2.42-2.50 g/cm3 for the Orgeuil meteorite (Miyazaki et al., 2023).
  • Many large rocks over 10 meters in size are present across the entire surface, and the reflectance of Ryugu's surface material is only about 4.5%, which is darker than typical carbonaceous chondrites.
  • Absorption at 2.72 µm is observed across the entire surface, but the absorption is weaker than carbonaceous chondrites containing hydrated minerals.


  • Average Radius:About 450m
  • Density:1.19±0.02g/cm3
  • Porosity:50-60%
  • Reflectance of Surface Material:About 4.5%
  • Absorption across the entire surface at 2.72µm

An experiment was also conducted to create an artificial crater using a collision device. This allowed for the acquisition of information on the physical properties of the asteroid's surface material while simultaneously exposing subsurface material, thereby revealing the differences between the subsurface and surface materials. After creating the artificial crater, it collected samples from the area near the crater, where material ejected from the crater had accumulated.

Sample Recovery by Sample Catcher

After Hayabusa2 reached and touched down on the surface of Ryugu, it deployed the "Sampler Horn," a sample collection device. After contacting the surface of Ryugu, the Sampler Horn injects gas to scoop up material from Ryugu's surface and collect it. The material collected by the Sampler Horn is stored in the spacecraft's sample catcher.

First Touchdown (TD1): February 22, 2019
Hayabusa2 made its first touchdown on the surface of asteroid Ryugu. The landing site was named "Tamatebako." A metal bullet (projectile) was also fired, causing the surface material to bounce up, allowing the samples to be stored in the spacecraft's container. This was the world's first sample collection via touchdown.

Touchdown Site by the Hayabusa2 Spacecraft (Sample Collection Location)
Image Credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, National Institute of Advanced Industrial Science and Technology (AIST)

Second Touchdown (TD2): July 11, 2019
Based on information from the first touchdown, the sample collection site was reselected, and the second touchdown was performed at "Uchide no Kozuchi." Before this, in April, a metal mass was driven into the surface of Ryugu to create an artificial crater. At that time, underground material was flung into the air and scattered around the crater. The purpose of the second touchdown was to collect this subsurface material. The sample catcher of Hayabusa2 is a complex system that combines precise operations and technology to collect material from the asteroid Ryugu and bring it back to Earth. This mission has provided valuable information about small celestial bodies in the solar system and significantly contributed to scientific research.

Once the sample collection was completed through two touchdowns, Hayabusa2 commenced its return mission to Earth. The sample catcher was stored in the re-entry capsule containing the samples to be brought back. The capsule re-entered the Earth's atmosphere at a speed of 12 kilometers per second and was subsequently recovered on the ground.

Scientific Results from the Returned Samples

The collected and returned samples were partially provided for initial analysis, and more advanced (Phase 2) curation analysis and detailed analyses were conducted. The results have been published in scientific journals such as "Science" and "Nature Astronomy."

Initial Analysis Team:Specialized sub-teams were formed to achieve the scientific objectives of "Hayabusa2," focusing on uncovering the multifaceted value of the samples.
Phase 2 Curation Institutions:Conducted more detailed cataloging and measurements and analyses tailored to the characteristics of the particles.

Main Research Results of the Initial Analysis Team

Chemical Analysis Team (PI: Hisayoshi Yurimoto, Hokkaido University)

Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites.

The Initial Analytical Chemistry Subteam studied the chemical composition, isotopic composition, constituents' origin, age, and relationship to meteorites.

  • Rock type of Ryugu: Ryugu is comprised of the Ivuna-type carbonaceous. The Ivuna-type carbonaceous chondrites (CI meteorites) have a chemical composition ratio excluding gaseous components equal to that of the solar system as a whole, considered to be the standard material of the solar system. They are very rare meteorites, consisting of only nine of the tens of thousands of meteorites that exist on the Earth.
  • Composition of Ryugu: Ryugu is composed mainly of phyllosilicates (like serpentine) and contains large amounts of water (about 7%) and carbon (about 5%). Most of the minerals are secondary minerals by chemical reactions (aqueous alteration) between aqueous solutions and the primary minerals in the Ryugu parent body.
  • History of Ryugu: The aqueous alteration of Ryugu occurred about 5 million years after the birth of the solar system, and the temperature at that time is estimated to be about 40 ℃. Subsequently, the destruction of the parent body occurred, and scattered fragments gathered to form the asteroid Ryugu, which is thought to have partly evaporated the water from the clay minerals, the main constituent minerals. Since the formation of the asteroid Ryugu, the temperature of Ryugu samples is not thought to have risen above 100 ℃.
Elemental abundances in the Ryugu sample, normalized to the analytical values of CI chondrites. Points that sit above (below) 1.0 are elements that are present in larger (smaller) quantities than in CI chondrites (from Yokoyama et al., 2022).

Published in: Science
Title: Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites
Authors: Yokoyama, T. et al.
DOI: 10.1126/science.abn7850
Publication Date: June 9, 2022

Stone Material Analysis Team (PI: Tomoki Nakamura, Tohoku University)

Formation and Evolution of the Carbonaceous Asteroid Ryugu: Evidence from Returned Samples

The Initial Analytical Stone Subteam analyzed 17 particles of the Ryugu sample using cosmochemical and physical methods at a number of different universities and institutes, including five synchrotron radiation facilities and muon facilities in Japan, the U.S..

  • The team discovered liquid water trapped within crystals in the sample. This water was carbonated water containing salts and organic matter, which was once present in Ryugu parent body. This indicates that the Ryugu parent body was formed at the outer edge of the primordial solar system, where CO2 existed as ice.
  • The Ryugu samples contain a mixture of materials from the surface of the parent body before impact destruction and materials from the interior of the parent body.
  • Simulation of Ryugu formation and evolution: We measured the hardness, heat transfer, specific heat, and density of the Ryugu sample. The measured data were used to perform numerical simulations of the temperature change due to heating in the interior of the Ryugu parent body after its formation and the collisional destruction process to reproduce the Ryugu formation evolution on a computer. The Ryugu parent body accreted about 2 million years after the formation of the Solar System, and reached at ~50°C about 3 million years later to the start of the water-rock reaction.The size of the impactor that destroyed the Ryugu parent body, which was about 100 km in diameter, was at most 10 km in diameter, and that the present-day Ryugu is composed of material from a region far from the impact point.
Liquid consisting mainly of water and CO2 found inside a hexagonal iron sulfide crystal (iron sulfide) in a Ryugu sample. (A, B) CT images of vacancies in iron sulfide crystals. (C) Various ion species contained in the vacancies as measured by a mass spectrometer (the two pictures of the same molecular species show the ion species contained in the upper part of the vacancy on the left and in the middle part on the right). The crystal temperature was set to -120°C and the liquid in the vacancies was frozen for analysis. (D) After the analysis, the liquid in the vacancies was evaporated and the interior of the vacancies was observed. The results indicate that there are no solid components other than the liquid in the vacancy. (Credit: Tohoku Univ. NASA/JSC, SPring-8)

掲載誌: Science
Published in: Science
Title: Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples
Authors: Nakamura, T. et al.
DOI: 10.1126/science.abn7850
Publication Date: September 22, 2022

IOM Analysis Team (PI: Hikaru Yabuta, Hiroshima University)

The dark organic macromolecules in Asteroid Ryugu samples

The Initial Analysis Insoluble Organic Matter (IOM) subteam performed non-destructive (non-processed particulate analysis) and destructive (analysis of insoluble residues obtained by acid treatment of samples) analyses of Ryugu particles.

  • Dark organic macromolecules: The solid organic matter in the Ryugu sample shows polymeric structure consisting of aromatic carbons, aliphatic carbons, ketone groups, carboxyl groups, etc..
  • Chemical and isotopic composition of the solid organic matter: Insoluble organic matter in Ryugu is similar to that of primitive carbonaceous chondrite meteorites. The absence of graphite-like ordered structures indicates that Ryugu's organic matter was not subjected to heating events at high temperatures.
  • Chemical reactions in the Ryugu parent body: The nanoglobule and diffuse carbon were found to be regions were found adjacent to or mixed with phyllosilicates and carbonates. This is evidence of chemical reactions between water, organics, and minerals in the Ryuguu parent body. The chemical compositions and morphologies of solid organic matter are more diverse in Ryugu than in meteorites, suggesting that reactions between liquid water and organic matter in the Ryugu parent body proceeded under various conditions.
  • Organic matter formed in cryogenic environments: Positive isotopic anomalies of deuterium (D) and nitrogen-15 (15N), which are not found in terrestrial organic matter and occur only in low-temperature environments below -200°C, were detected in both particle and insoluble organic residues of Ryugu samples. At least some of the organic matter of Ryugu have formed in cryogenic environments such as interstellar medium or presolar nebula.
  • The chemical evolutionary history of Ryugu: The distribution of hydrogen isotopic compositions of insoluble residues isolated from Ryugu samples is similar to that of carbonaceous meteorites that have experienced reactions with water on their parent bodies. The chemical evolution of organic matter compositions has been revealed as follows. The repeated processes of transformation of primary organic matter produced in molecular clouds and disks, and the synthesis of new organic matter from the transformed molecules.
Images of insoluble carbonaceous residues isolated from the intact Ryugu aggregates (A0106) by HF/HCl treatment. (a) The Ryugu carbonaceous residue in a mini glass vial. (b) An overhead image of the Ryugu carbonaceous residue aliquots transferred in another mini vial.

Published in: Science
Title: Macromolecular organic matter in samples of the asteroid (162173) Ryugu from returned samples
Authors: Yabuta, H. et al.
DOI: 10.1126/science.abn9057
Publication Date: February 24, 2023

Volatile Gas Analysis Team (PI: Ryuji Okazaki, Kyushu University)

Noble gases and nitrogen in samples from asteroid Ryugu record volatile sources and recent surface evolution.

The Initial Analytical Gas Subteam measured the infrared spectroscopy and electron microscopic observations, noble gas isotopic compositions, and nitrogen isotopic compositions of Ryugu particles. Based on these measurements, the team studied the origin of Ryugu materials and the evolution of surface materials after the formation of Ryugu.

  • Primordial noble gases and nitrogen isotope ratios: The results of noble gas isotope analysis revealed more primordial noble gases than any other meteorite reported so far, which were taken up by the material in space during the formation of the solar system. Nitrogen isotopic compositions vary from sample to sample, indicating that a wide variety of nitrogen-preserving materials are still preserved in the Ryugu samples. In addition to noble gases from the formation of the solar system, the samples also contained two types of noble gases: those produced by galactic cosmic rays and those originating from the solar wind. In the first touchdown sample, which is the most surface material, traces of long-term solar wind irradiation were found, and the noble gas isotopes clearly showed the difference from the non-surface material sample recovered in the second touchdown.
  • The average duration of Galactic cosmic ray irradiation was found to be about 5 million years based on the amount of neon in the Galactic cosmic rays. This is consistent with the formation age of craters on the Ryugu surface, which have formed in near-Earth orbit, meaning that Ryugu moved into near-Earth orbit about 5 million years ago and that the surface materials have not undergone major changes since then. The results of the noble gas analysis suggest that Ryugu approached the Sun more than 1 million years ago, and the reddish material in the mid-latitude region of Ryugu reported by visible spectroscopic observations is considered to have been reddened by heating in the solar neighborhood.
The Nitrogen isotope composition of the Ryugu sample grains (vertical axis, measured as difference from the Earth’s atmosphere in parts per thousand) vs the inverse nitrogen abundance (weight ratio: horizontal axis). The Ryugu grains (orange circles, green inverted triangles, red circle) each show a different nitrogen composition. CI chondrites (grey and blue squares) and CM chondrites (purple triangles, purple enclosed area) is also shown for reference. If mixed with the Earth’s atmosphere, the analysis data would move in the direction indicated by the blue arrow, but the effect would not be visible.

Published in: Science
Title: Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution
Authors: Okazaki, R. et al.
DOI: 10.1126/science.abo0431
Publication Date: October 22, 2022

World’s first asteroid gas sample delivered by the Hayabusa2 mission: A treasure box from Ryugu

The Initial Analysis Gas Subteam conducted mass spectrometry and gas sampling on the gas trapped in the sample container brought back to Earth by the Hayabusa2 spacecraft.

  • The isotope ratio of helium with an atomic mass of 3 (3He) is 100 times higher than in the Earth’s atmosphere. The isotope composition of neon also differed from that of the Earth’s atmosphere.
  • On the other hand, the helium, neon, and argon elemental abundances and helium isotope ratios in the container showed that the gas contained a mixture of the solar wind and the Earth’s atmosphere that was mixed into the container after the return to Earth. Based the amount of helium in the container, the trapped gas most likely originated in the solar wind that was liberated from the pulverisation of the surface of the grains in the Ryugu sample.
  • The Hayabusa2 mission has become the first in the world to return gaseous components from a near-Earth orbit back to Earth.
Helium and neon isotopic composition of the Hayabusa2 sample container gas (green). The composition can be explained by a mixture of the Earth’s atmosphere and the solar wind. Solid lines show the result of mixing the solar wind and Earth’s atmosphere in different ratios. Jupiter’s atmosphere, primordial noble gases (P1), pre-solar noble gases (P3, HL) and galactic cosmic-ray produced noble gases (GCR-produced) are shown for comparison.

Published in: Science Advances
Title: First asteroid gas sample delivered by the Hayabusa2 mission: A treasure box from Ryugu
Authors: Okazaki, R. et al
DOI: 10.1126/sciadv.abo7239
Publication Date: October 22, 2022

SOM Analysis Team (PI: Hiroshi Naraoka, Kyushu University)

Organic molecule compositions in samples of asteroid Ryugu

The initial analysis soluble organic matter (SOM) subteam analyzed the aggregate powder samples from the first touchdown sampling in universities and research institutes in Japan, the United States, and Germany using high-resolution mass spectrometry and chromatographic methods.

  • The average composition of Ryugu: C, H, N, S, and pyrolytic O were about 20 wt% in total, and their stable isotope compositions were similar to those of carbonaceous meteorites of the Ivena type (CI).
  • Organic matter in Ryugu: Among the 20,000 compounds dissolved in methanol, CHOS, CHNO, and CHNOS were relatively abundant, and small molecules such as methylamine, ethylamine, and acetic acid were identified. The detection of these highly volatile molecules on the asteroid surface indicates that they exist as molecular salts. In addition to protein-constituent amino acids (such as alanine) used by life on Earth, non-protein-constituent amino acids such as isovaline were also found. Alkylbenzenes and polycyclic aromatic hydrocarbons such as naphthalene, phenanthrene, pyrene, and fluoranthene were the main hydrocarbons present. Their pattern is similar to that of hydrothermal crude oil on Earth, suggesting that they were influenced by water on the Ryugu parent body.
  • Organic matter transport from Ryugu: It is possible that organic compounds were separated during the interaction of fluids and minerals on the Ryugu parent body, and that organic molecules on the Ryugu surface may be transported to other bodies, as materials have been observed to be ejected into space from the asteroid's surface in various processes. Organic molecules on Ryugu surface may be transported to other celestial bodies.
Conceptual organic molecules found in surface samples from the asteroid Ryugu (JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST, NASA, Dan Gallagher.)

Published in: Science
Title: Soluble organic molecules in samples of the carbonaceous asteroid (162173) Ryugu
Authors: Naraoka, H. et al.
DOI: 10.1126/science.abn9033
Publication Date: February 24, 2023

Urasil in the carbonaceous asteroid 162172 Ryugu

The Initial Analysis Soluble Organic Matter (SOM) subteam analyzed solutions of aggregate powder samples obtained from the first and second touchdown samplings of Ryugu with hot water using high-performance liquid chromatography/electron spray high-resolution mass spectrometry.
As a result, we succeeded in detecting uracil, one of the nucleobases in the RNA of all earth life, and vitamin B3 (niacin), one of the coenzymes essential for the metabolism of life. These detections provide a real picture of the chemical evolution of organic molecules, and strongly support the theory that components supplied by extraterrestrial materials such as carbonaceous meteorites (i.e., asteroid fragments) were the materials for the ultimate mystery in science: how the first life on the primitive Earth was created before the birth of life.

Published in: Nature Communications
Title: Uracil in the carbonaceous asteroid (162173) Ryugu
Authors: Oba, Y. et al.
DOI: 10.1038/s41467-023-36904-3
Publication Date: February 15, 2023

Sand Material Analysis Team (PI: Takaaki Noguchi, Kyoto University/Kyushu University)

A dehydrated space-weathered skin cloaking the hydrated interior of Ryugu

A large number of samples are less than 1 mm in diameter from the asteroid Ryugu recovered by the asteroid explorer Hayabusa2 were examined to determine what percentage of them retained their original surface on the asteroid. Most of the specimens were fragments of stones that had been destroyed by impact during sample recovery, but about 6% of the specimens retained their original surfaces.

  • Two types of surface textures: "Smooth layer, a relatively smooth surface with small holes of about 0.1 micrometer" and "Frothy layer, a surface of stone or sand that looks fused and foamy (bubbled)”.
  • Reproduction experiments using meteorites and other materials. have clarified the causes of these two types of textures. Smooth surface is a space weathering texture formed by solar wind irradiation. Frothy layer is other space-weathered structure formed by heating and melting the hydrous layered silicate minerals contained in Ryugu, which are strongly heated and decompose by releasing water vapor.
  • Different tanning: C-type asteroid Ryugu shows Not only are the effects of space weathering caused by micrometeoroid impacts and heating more pronounced on the C-type asteroid Ryuguu than on the S-type asteroid Itokawa, but this space weathering causes dehydration on the surface of C-type asteroids. This indicates that each non-atmospheric bodies shows differently tanning depending on their individual characteristics.
  • Space weathering of asteroids: C-type asteroids are the most common in the main belt between Mars and Jupiter, where asteroids are most concentrated. Most of them have water molecules or hydroxy groups (OH) observed from ground-based observations, but about 40% of them do not. We found that space weathering of C-type asteroids should be taken into account as the cause of their non-observation.
Space weathering of a Ryugu grain. The smooth layer on the right side of the dotted line has been subjected to space weathering from solar wind irradiation. The frothy layer visible on the left side has experiences space weathering from micrometeoroid impacts, and contains deposits of thin layers of melted rock. This backscattered electron image allows us to read the complex history of Ryugu.

Published in: Nature Astronomy
Title: A dehydrated space weathered skin cloaking the hydrated interior of Ryugu
Authors: Noguchi, T. et al.
DOI: 10.1038/s41550-022-01841-6
Publication Date: December 19, 2022

Main Research Results of Phase 2 Curation Institutions

Phase 2 JAMSTEC Kochi Core Research Institute Team (PI: Motoo Ito, JAMSTEC)

Asteroid Ryugu: A Visitor from the Outer Solar System - Asteroid Record Deciphered by Multi-Institutional Analysis

  • The mineral assemblage of the analyzed samples indicates that Ryugu particles underwent large-scale water metamorphism after their formation.
  • The hydrogen and nitrogen isotopic compositions of the fine-grained minerals and the organic material in the region indicate that the constituent materials of the Ryugu grains were formed in the outer solar system.
  • The results of this study suggest that the Ryugu grains were formed at the outer edge of the solar system and that aliphatic carbon-rich organic matter is concentrated in the coarse-grained hydrous silicate minerals. This feature has not been observed in previous studies of meteorites, and is considered to be unique to Ryugu Celestial Body.
  • These results suggest that coarse-grained hydrous silicate minerals in primitive bodies may have served as a cradle for organic matter and water, which were then transported to Earth in their original state.
(upper left) The largest Ryugu particle A0002 distributed, (lower left) synchrotron X-ray CT image obtained at SPring-8, (middle) minerals formed by water in Ryugu particles: red: hydrous silicate minerals, green: carbonate minerals, blue: iron oxide minerals, yellow: sulfide minerals, (right) white square area in the middle figure is enlarged with an electron microscope Figure (Ito et al. (2023))

Published in: Nature Astronomy
Title: A pristine record of outer Solar System materials from asteroid Ryugu's returned sample
Authors: Ito, M. et al.
DOI: 10.1038/s41550-022-01745-5
Publication Date: August 15, 2022

Phase 2 Okayama University Planetary Material Research Institute Team (PI: Eizo Nakamura, Okayama University)

Origin and Evolution of the Asteroid Ryuguu - A Comprehensive Geochemical Analysis of the Evolution of Materials in the Solar System

A detailed comprehensive geochemical analysis was performed on 16 grains recovered from asteroid Ryugu, the target of the Japanese asteroid explorer Hayabusa2 mission. The results revealed that the asteroidal material sample retains evidence of complex physico-chemical processes that occurred from before the formation of the Solar System through to the present, providing a new picture of the evolution of material in the Solar System, including that of the origin of life.

  • The sample is mainly composed of hydrous phyllosilicate minerals, with a porosity of approximately 50%.
  • The chemical composition of the asteroid is similar to that of CI chondrites. It has also been confirmed that the sample contains material collected not only from the surface of Ryugu, but also from the interior material that was ejected as a result of the formation of the artificial crater.
  • Contamination from the tantalum projectiles used during the sampling was seen in part of the sample, but no contamination from the copper impactor (SCI: Small Carry-on Impactor) that was used to create the artificial crater was observed.
  • Micron-sized organic material originating from interstellar clouds showing hydrogen, carbon and nitrogen isotopic anomalies was detected.
  • The primordial features that include interstellar material and solar system progenitors that made up the primitive solar system were retained. The progenitor of the asteroid Ryuguu was found to be an icy object in the outer solar system where ice-rich dust containing organic matter and silicates accumulated (ice progenitor). The size of the ice precursor was several tens of kilometers, and it is thought that it underwent water alteration and was crushed to form a cometary nucleus of several kilometers in size during the period up to about 2.6 million years after the formation of the solar system. After moving into near-Earth orbit, ice sublimated from the cometary nucleus, and low-density material with many voids was formed due to the reduction in the size of the object and the re-deposition of material associated with the solid-gas jet.
  • Organic materials are ubiquitous in the samples, which are subjected to cosmic weathering by cosmic rays and solar wind exposure, and characterize the albedo properties of the asteroid's surface.
Origin and evolution of the asteroid Ryugu. Icy planetesimals forming in the outer Solar System from interstellar matter and Solar System precursors, and after excessive aqueous alteration of their interiors, fractured and reached near-Earth orbit as comet-like asteroids, which evolved into rubble-accumulator-like asteroids due to the sublimation of ice.

Published in: Proceedings of the Japan Academy, Series B
Title: On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective
Authors: Nakamura, E. et al.
DOI: 10.2183/pjab.98.015
Publication Date: June 10, 2022

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