In December 2020, the Extraterrestrial Samples Curation Center (ESCuC) received a sample from the asteroid Ryugu retrieved by the Hayabusa2 spacecraft.
Preparation for Acceptance of the Hayabusa2 Return Sample
In 2015, the Astromaterials Science Research Group (ASRG) started to specific preparation to accept the Ryugu return sample. Major preparations were setup a clean room and a clean chamber(s) for Hayabusa2. At the beginning of the preparation, we discussed scientific requirements with researchers from several universities and research institutes and completed facilities to meet the requirements in 2018. While the clean chamber for Hayabusa was composed of 2 units (CC1 and CC2), the clean chamber for Hayabusa2 is composed of 5 units (CC3-1, CC3-2, CC3-3, CC4-1, and CC4-2). CC3-1 is for introducing the sample container and CC3-2 is for collecting and storing some parts of sample in a vacuum atmosphere. These functions are for the Hayabusa2 science special request. CC4-1 and CC4-2 are chambers for handling samples in high level pure nitrogen atmosphere. Design of CC4-1 was based on CC2 for Hayabusa, though it had been changed based on experience so far, making it possible to handle samples more reliably. CC4-2 was newly designed chamber that the ceiling of it is all glass window to observe samples. We, ASRG, made thorough preparations in a wide range of areas, including installing various measuring and analysis equipment in the clean chamber, developing sample handling tools, examining equipment cleaning methods, and making efforts to master operations through rehearsals by preparing operational procedures.
Acceptance of the Re-Entry Capsule and Retrieval of the Sample Catcher
The re-entry capsule delivered to Australia by Hayabusa2 were cleaned by the sampler team (SMP) and gas was collected inside the sample container. They were then transported to ESCuC in Japan and the sample containers were taken out in a clean room. A sample container is a vacuum sealed container that contains a sample catcher. We, SMP and ASRG, thoroughly cleaned the surface of the container, set it in the container lid opening device, and installed it in CC3-1. The sample container is a vacuum container and has a function to protect the sample in the sample catcher from contact with the atmosphere on the earth. In the course of this series of work, if the lid of the container was opened even a little, the earth's atmosphere might enter, and the samples might be contaminated. However, we were able to introduce the container into CC3-1 safely through careful work. After introduction, CC3-1 was placed in a high vacuum atmosphere, the container lid was opened, and the sample catcher was retrieved from the container.
Sample Recovery from the Sample Catcher
The sample catcher collected from the sample container in CC3-1 was moved to CC3-2. In CC3-2, under a vacuum, a cover on Room A of the sample catcher was opened, and materials in the catcher were observed. The sample catcher has three rooms from A to C to store samples, and room A is the largest one. Some particles were then collected using forceps. The samples collected here are stored in a vacuum atmosphere for long-term storage for future research. After these samples were collected, the sample catcher was moved to CC3-3. The sample catcher was disassembled by glove operation under a nitrogen atmosphere in CC3-3, followed by CC4-1 and CC4-2, and samples were collected from Room A and other rooms. The amount of sample collected was about 5 grams, far exceeding the expected 100 milligrams. In addition, in the Itokawa fine particles (about 50 micrometers) were the main ones, but this time, large particles of several millimeters were obtained. Sample handling tools used this time have been newly developed for the Ryugu sample.
As of December 2020, we are sorting samples and just started initial description in CC3-3, CC4-1 and CC4-2. These three chambers are equipped with a balance, optical microscope, FTIR (Infrared microscope + Fourier transform infrared spectrophotometer), and MicrOmega (near-IR hyperspectral microscope) and can measure samples without contamination or destruction. The initial description which is measuring weight, observing appearance, color and size, and analyzing IR reflection spectra here, is performed to identify the characteristics of samples. It is expected to provide evidence that the sample is derived from Ryugu, and it also serves as information for the distribution of the sample to research institutions and researchers.
Initial Analysis and Phase2 Curation
From the middle of 2021, samples after the initial description will be provided to the Hayabusa2 project's initial analysis team (researchers selected from collaborating universities and research institutions). In the initial analysis, various high-level analyses will be carried out, and it is expected that knowledge on the formation process of the asteroid, the origin of water contained in the asteroid, and the history of the solar system will be obtained. In addition, ASRG has established a cooperative system called Phase2 Curation with the research institutions with which it has concluded a partnership agreement and plans to conduct high-level analysis (Detailed Description). Phase2 Curation are also working to improve sample handling technology.
Access to Ryugu Sample Information and International Public Research
Information on the initial description will be registered in a database and released on the Internet. From the middle of 2022, ASRG will start international public research which is called as the International Announcement of Opportunity (AO). This framework makes it possible for ordinary researchers to conduct research using Ryugu sample.
Curation Techniques and Tools
Clean Chamber for Hayabusa2
It is consisted of vacuum chambers and nitrogen atmosphere glove boxes. The main difference from the clean chamber for Hayabusa is that the sample can be collected and stored from the sample under vacuum, and sample handling performance is improved by the design change. In order to meet these requirements, the chamber for Hayabusa2 has a 5 chambers connection structure. Also, FTIR and MicrOmega are mounted on expansion chambers for the initial description, which is also different from the chamber for Hayabusa.
Vacuum Tweezers and Loop Shaped Needle
Since most of the Itokawa samples were fine particles of about 50 micrometers in size, the sample could be manipulated by the electrostatic control manipulator. Ryugu specimens are several micrometers to several millimeters, mainly several hundred micrometers. Vacuum tweezers (pickup tool) and loop shaped needle are suitable tools for handling samples of that size. Vacuum tweezers are tools to attach a sample to the tip of a pencil by suction force and operate it. The loop shaped needle is a tool originally developed by ASRG. The tip of the stainless-steel needle is bending into a loop. Linear needles are well known as a conventional sample handling tool, but by deforming the tip shape, the adhesion efficiency of samples is increased.
Itokawa samples are stored in a row of multiple samples on a slide glass (quartz glass) with a square grid engraved on it. For the storage of Ryugu sample, Phase2 members of JASRI/Spring-8 and ASRG discussed the advantages and disadvantages of the conventional method and developed a new container. The material is sapphire, and the shape is changed to a dish. Each sample is individually stored in each dish with a cover. This structure can prevent mixing between samples.
When the sample is removed from the clean chamber, we need a special container to avoid samples to touch the atmosphere. Phase2 Curation Team KOCHI developed a new container and named them Facility to Facility Transfer Container (FFTC). The main feature is that the upper surface of the container is a quartz window, enabling observation of samples without opening the container. By not opening the container, not only save time to open, but it also eliminates concerns about sample contamination and sample loss due to airborne dust. This container is considered not only transportation but also subsequent analysis.
- Hayabusa2 Curation