Astromaterials Science Research Group｜ISAS

Curation

Hayabusa2 Curation

The materials brought back from the asteroid Ryugu by the spacecraft Hayabusa2 are being accepted at the Extraterrestrial Sample Curation Center. As a result of the sample recovery from the sample container, it has been confirmed that the materials far exceed the minimum requirement of 0.1 g for the Hayabusa2 mission and contain about 5 g of substance [1]. The Extraterrestrial Sample Curation Center described these substances (size, shape, weight, optical images, NIR spectroscopic data, etc.) as Ryugu samples. It made them publicly available in a sample catalog for public research. The Ryugu samples are expected to provide new insights into the origin and evolution of the solar system, the formation of asteroids, and return samples. This section explains the handling methods and results of the Ryugu samples.

Preparation for the Acceptance of Hayabusa2 Return Samples

The Extraterrestrial Materials Research Group began seriously considering the acceptance facilities for the return from Ryugu in 2015. After a year of discussions with university and institute researchers, the primary preparations were established, including the cleanroom and chamber specifications. The cleanroom was constructed from April to November 2017, and the clean chamber was manufactured from March 2017 to March 2018 [2-4].

Cleanroom

  • The cleanliness class is 1000 (Federal Standard of the USA), equivalent to Class 6 in ISO 14644-1.
  • Uses ULPA filters. A pressure difference is maintained with adjacent non-clean rooms (positive pressure management) to prevent the intrusion of atmospheric particulates.
  • Temperature 22 ± 2°C, humidity 50 ± 10% RH. High humidity is maintained to suppress static electricity.
  • Grating floor. Piping for high-purity nitrogen gas, compressed air, cooling water, exhaust, etc., is installed under the grating floor.
  • Equipment that degrades the cleanroom environment (vacuum pumps, etc.) is placed outside the cleanroom for isolation.

Clean Chamber

  • Comprises five connected rooms (Chamber 3-1, 3-2, 3-3, 4-1, and 4-2).
  • Room 3-1 opens the sample container in a vacuum, Room 3-2 recovers samples from the sample catcher for long-term storage in a vacuum, Room 3-3 switches from vacuum to nitrogen atmosphere, and Rooms 4-1 and 4-2 handle detailed sample operations under atmospheric pressure nitrogen with glove operations.
  • CC4-2 is permanently equipped with an optical microscope and scale. CC3-3 is connected to the MicrOmega infrared spectroscopy microscope chamber, and CC4-2 to the FTIR spectrometer chamber.
  • Equipped with gate valves between each room, allowing for atmosphere isolation and independent atmosphere maintenance.
  • The chamber's inner surface is composite electrolytic polished to maintain the cleanliness of the atmosphere and minimize sample contamination.
  • The chamber's primary material is stainless steel. The gloves are primarily Viton-coated butyl.
  • As for the chamber's internal materials, materials other than those used in the sample retrieval device are avoided as much as possible.
Hayabusa2 Clean Chamber
Facility

Re-entry Capsule Reception and Sample Catcher Recovery

The Hayabusa2 spacecraft, after its first touchdown (TD1) on February 22, 2019, collected surface materials from asteroid Ryugu and, following the creation of an artificial crater using an impactor, conducted its second touchdown (TD2) on July 11, 2019, to collect subsurface materials. After leaving Ryugu, Hayabusa2 delivered the re-entry capsule containing the samples to the Woomera Desert in South Australia on December 6, 2020. The re-entry capsule was recovered five hours after landing, and initial processing, including removal and surface cleaning of the sample container and safety checks, was carried out at a local quick-look facility. The vacuum-sealed sample container protects the sample catcher and the samples inside from contamination by Earth's atmosphere [5]. On December 7, a pinhole was made in the bottom of the sample container to analyze the atmosphere inside the container (retained volatile components) [6-7]. This confirmed that the sample container was in a vacuum state, remained sealed during re-entry, and was protected from terrestrial contamination. Subsequently, the sample container was air-transported to JAXA's Sagamihara Campus's Extraterrestrial Sample Curation Center, arriving about 57 hours after the capsule's landing [1-3].
In the cleanroom of the Extraterrestrial Sample Curation Center, the ablator covering the outer lid of the sample container was removed, and the container was set in a lid-opening mechanism. The sample container's inner lid and container body are pressed together by spring pressure, with a newly developed metal sealing for vacuum sealing [5]. The lid-opening mechanism is a device that removes the spring and the outer lid while maintaining the seal inside the container, ultimately connecting to the Clean Chamber Room 3-1. The surface of the sample container was thoroughly cleaned. When the outer lid was removed, particles thought to be Ryugu samples, about 2 mm in size, were found in the gap between the inner lid and the main body of the container (later analyzed in detail) [8]. After thoroughly cleaning the sample container's surface, it was introduced into Clean Chamber Room 3-1 on December 11. Swift and careful operations were carried out throughout the entire process from Australia to the Curation Center, as any slight opening of the container lid could have allowed Earth's atmosphere to infiltrate and contaminate the samples. Once the sample container was introduced, the opening of Room 3-1 was closed, and the room was evacuated to a high vacuum (<10-5 Pa). After confirming the vacuum state, the inner lid of the sample container was opened on December 14, 2020 [1-3].

Sample Recovery from the Sample Catcher

After opening the inner lid of the sample container in Chamber 3-1, the sample catcher was removed from the container. Upon removal, fine black powder, believed to be Ryugu samples, was observed at the bottom of the container. This powder is being stored continuously under vacuum in Chamber 3-1. After removing the container, a transfer rod transferred the sample catcher from Chamber 3-1 to Chamber 3-2. In Chamber 3-2, the cover of Chamber A of the sample catcher was removed. Numerous black particles were observed inside Chamber A. The sample catcher has three chambers - A, B, and C - each capable of storing samples independently, with Chamber A being the largest [5]. Several millimeter-sized particles observed in Chamber A were segregated onto a quartz glass sample dish using tweezers (magic hand). These particles are stored under a vacuum in Chamber 3-2 for future research. On December 16, 2020, the sample catcher was transferred to Chamber 3-3 using the transfer rod.

In Chamber 3-3, following the receipt of the sample catcher, the vacuum exhaust was stopped, and the chamber was filled with high-purity nitrogen gas to adjust it to atmospheric pressure. After the departure of the sample catcher, Chambers 3-1 and 3-2 were each isolated by gate valves and continued to maintain a vacuum state with independent vacuum exhaust systems. In Chambers 3-3, glove operations became possible once the atmospheric pressure was attained and the sample catcher was detached from the inner lid of the sample container. Subsequently, the total weight of the samples was determined to be 5.424±0.217 g after measuring on a weighing device in Chamber 4-2 and deducting the weight of the sample catcher parts. This weight significantly exceeds the minimum requirement of 0.1 g set by the "Hayabusa2" project. Notably, while the previous "Hayabusa" project primarily yielded microparticles (about 50 μm), this project has successfully retrieved larger particles, some of which are several millimeters.

Initial Description of Ryugu Samples

Sample Recovery in Chambers 4-1 and 4-2**: Under the atmospheric nitrogen atmosphere in Chambers 4-1 and 4-2, glove operations facilitated the disassembly of the sample catcher and the recovery of samples into containers (sapphire glass sample dishes). Initially, three dishes of powder (aggregate) samples from Chamber A, one from Chamber B, and three from Chamber C were recovered, along with 15 larger particles. These samples were named and analyzed using optical microscopy, weighing, infrared microscopy with Fourier-transform infrared spectrometry (FTIR), MicrOmega infrared spectroscopy, and a multicolor visible spectrometer. These analyses were non-destructive and conducted without exposing the samples to the atmosphere, maintaining the nitrogen atmosphere of the clean chamber.

Insights from the Initial Description

  • We determined the average bulk density of Ryugu samples to be 1.282±0.231 g/cm3. This confirmation was based on the observed characteristics of dark surfaces in optical observations and absorption profiles at 2.7 and 3.4 μm in near-infrared reflection, which matched the overall average of asteroid Ryugu. Additionally, the absence of sub-millimeter CAIs and chondrules suggests that Ryugu is most similar to CI chondrites, exhibiting low reflectance, high porosity, and brittle characteristics (Yada T. et al., 2022)[2].
  • MicrOmega allowed us to observe the mineralogical and molecular characteristics in the near-infrared range (0.99-3.65 μm) at a scale of tens of micrometers. The results revealed relatively large absorptions at 2.7 μm (indicative of OH groups) and 3.4 μm (indicative of C-H groups, i.e., organic material). Features such as calcium and iron carbonate minerals and NH-rich compounds were also detected (Pilorget C. et al., 2022)[12].
  • The results of sample recovery and shape observations through optical microscopy are consistent with expectations based on the sampling conditions by the Hayabusa2 spacecraft, observations by the MASCOT lander and MINERVA-II rovers, observations from onboard cameras, and polarimetric observations from Earth. This suggests that the samples recovered in Sample Catcher A and C compartments correspond to samples obtained in TD1 (surface layer) and TD2 (subsurface layer), respectively (Tachibana S., et al., 2022)[1].
  • Using a multispectral analysis system allowed for direct comparisons between remote sensing (ONC-T) and returned samples. Multispectral analysis of Ryugu samples from compartments A and C revealed that the measured average spectrum of Ryugu samples is flat and matches the global average spectrum of asteroid Ryugu observed by ONC-T. The reflectance in the 550 nm band (v-band) of the returned samples averaged 2.4%, which is higher than the global average spectrum of asteroid Ryugu observed by ONC-T (Cho Y. et al., 2022)[15].
  • Based on surface observations, 205 sample particles were classified into four forms: dark, glossy, bright, and white. Approximately 95% belonged to the dark group, which generally matches observations made by MASCOT/CAM. The bright to dark groups ratio between TD1 and TD2 showed a difference of about 1.7 times, potentially reflecting variations in space weathering at sampling sites (Nakato A., et al., 2023)[10].
  • For both powders and individual particles, reflection spectra obtained by Fourier transform infrared spectroscopy (FTIR) were analyzed using principal component analysis (PCA). The results indicated high homogeneity in Ryugu samples. The average spectrum exhibited absorptions in four bands at 2.7, 3.05, 3.4, and 3.95 μm, suggesting the presence of hydroxyl groups, organic material, and carbonate minerals. Some types exhibited distinctive spectra and were classified into three groups: high reflectance, carbonate minerals, and hydroxides with broad OH absorptions (Hatakeda K., et al., 2023)[11].
  • An initial description of 637 Ryugu particles (38% of the total recovered samples) determined the average bulk density of returned particles to be 1.79±0.31 g/cm3. The average bulk densities of 392 particles from Compartment A and 245 particles from Compartment C were slightly different, measuring 1.81±0.30 and 1.76±0.33 g/cm3, respectively. Using an average bulk density of 1.79 g/cm3 for the p

Research Activities

Initial Analysis and Phase 2 Curation

After the initial description, parts of the Ryugu samples underwent detailed analysis by the "Hayabusa2" project's initial analysis team. Additionally, in collaboration with partnered research institutions, the extraterrestrial material research group has been conducting a comprehensive higher-level analysis (detailed description) within a framework called Phase 2 curation. This phase aims to cover all the characteristics of the Ryugu return samples. The initial analysis and Phase 2 research have provided insights into various aspects, such as the formation process of asteroid Ryugu, the origin of water contained in the asteroid, and information related to the solar system's history.

Sample Catalog and the Announcement of Opportunity

The initial description information is managed in a database and published online as a sample catalog. Starting in 2022, international research proposals (AO) are being accepted biannually, inviting research proposals from researchers worldwide. The amount of samples allocated for AO is 15%, as agreed upon with the Hayabusa2 Sample Allocation Committee (HSAC).

  • First AO**: Of the 57 proposals submitted, 40 were accepted, and 74 particles (totaling 229.5 mg) were allocated to the researchers who submitted these proposals.
  • Second AO**: Of the 47 proposals submitted, 38 were accepted, and 53 particles, along with 10 aggregate samples (totaling 217.0 mg), were distributed.
  • Third AO**: Of the 23 proposals submitted, 17 were accepted, and 13 particles, along with 10 aggregate samples (totaling 117.7 mg), were allocated.
  • This process of international proposals and distribution of Ryugu samples signifies a global collaborative effort in advancing our understanding of asteroids and their role in the solar system, enriching scientific knowledge and research opportunities in planetary science.

Curatorial Techniques and Tools

Cleaning and Environmental Evaluation

Extensive contamination assessments are conducted at every stage, from sample collection on the spacecraft to sample distribution. The Extraterrestrial Sample Curation Center pays utmost attention to cleaning instruments and environmental evaluation. Instrument cleaning involves using organic solvents and ultra-pure water and performing ultrasonic cleaning at multiple frequencies to remove tiny particles and organic matter. Additionally, heat cleaning with an alkaline solution is also conducted for stainless steel and glass products that come into direct contact with samples. Baking in high-temperature furnaces, plasma cleaning, and ozone cleaning are used when necessary. Regular environmental assessments of the clean room and the desiccators' storage instruments ensure the purity of the returned samples.

Vacuum Tweezers, Loop Needles, and Spatulas

The Extraterrestrial Material Research Group has designed and manufactured vacuum tweezers and loop needles for handling Ryugu samples. These tools are suitable for handling samples ranging from a few hundred micrometers to a few millimeters in size. Vacuum tweezers, the most frequently used tool, operate by adhering samples to the tip of a straight tube via suction force. Although based on commercially available products, they have been customized in material and design to minimize sample contamination in the clean chamber. Considering operability, they also feature a foot pedal mechanism for opening and closing the vacuum valve. Loop needles, an original tool, are made by forming the tip of a stainless steel needle into a loop. While straight needles are commonly known, modifying the tip shape increases sample adherence efficiency. Spatulas scoop powder from sample containers for samples less than 1 millimeter, often handled as powder rather than individual particles. These spatulas have been designed through repeated testing with mock samples to collect powdered samples efficiently. Tools that come into direct contact with samples also undergo demagnetization and measurement of magnetic susceptibility to consider the effects of magnetization on the samples.

Sample Storage Dishes

The primary containers used for storing samples were co-developed with JASRI/Spring-8. These containers are dish-shaped and made of glass. Sapphire glass is chosen as the glass material to avoid interfering with spectroscopic measurements. Various sizes of these dishes are prepared, depending on the size and quantity of the samples being stored. Additionally, the design of these sample dishes includes lids, preventing spillage and unintended mixing of samples. Unique holders have also been developed to handle multiple sample dishes collectively. These tailor-made solutions ensure the safe and efficient handling and storage of delicate extraterrestrial samples.

Sample Transport Containers: FFTC

While transferring samples from the clean chamber is sealed within containers to maintain a controlled atmosphere. The Phase 2 Curation team in Kochi has developed specialized containers for this purpose, known as FFTC (Facility to Facility Transfer Container). These containers have a unique feature - a quartz glass window on the top surface, allowing for sample observation without opening the container. This design enables sample observation without opening the container and eliminates concerns about sample contamination from airborne particles and the risk of sample loss.

References

Curation

  • TOP
  • Hayabusa2 Curation