Asteroid explorer, Hayabusa2,reporter briefing

April 27, 2021
JAXA Hayabusa2 ProjectTopics
Introduction to spectral profile resultsfrom the Ryugu samples in curationand scientific achievements, and status
report of the spacecraft.

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Contents
1. Overview of the current project status
2. Spectral profiles of the Ryugu sample
3. Scientific results: distribution of hydrous minerals on Ryugu
4. Scientific results: polarization observation with ground-based telescope
5. Spacecraft status
6. Future plans

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31. Overview of the current project status
 Spacecraft operation• Spacecraft operation is normal and travel continues smoothly towards thedestination of the Extended Mission. The plan for future ion engine
operations was reviewed, and the start of the next operation was changed
to the end of May.
 Curation work
• High definition optical microscope images continue to be acquired of theparticle/bulk aggregate samples returned from Ryugu.
• The results of observations of the returned sample show characteristics ofthe hydrous and carbonate minerals that indicate the presence of water inthe Ryugu parent body (details on following pages)
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2. Spectral Profiles of Ryugu Return Sample• Spectroscopy of bulk return sample has started as part of the initial description
under non-destructive and non-contaminated conditions since January 2021
• Performed with FTIR (NIR continuous spectroscopy) and MicrOmega (NIRhyperspectral microscopy).
• The same features are found in both spectral profiles– 2.7µm absorption, related to water (-OH), the similar feature observed inNIRS3 spectrum– 3.4 µm absorption, related to organics (-CH) and/or carbonate (-CO3)• These features are the evidence that the returned sample did originate from Ryugu.
• Indicative of a primitive sample of the Solar System, containing water or carbon
related materials (waiting for in-depth analyses with higher accuracy andresolution)
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2. Spectral Profiles of Ryugu Return Sample• Examples of spectra (FTIR & MicrOmega)– Absorption features seen at 2.7 and 3.4 µm

2021/4/27© MicrOmega/IAS/CNES

5 mmChamber A

Wavelength-selected image enhance (few) grains withspecific composition, within bulk material.
[Red] : OH-enriched grain

Hayabusa2 reporter briefing62. Spectral Profiles of Ryugu Return Sample• 3D movie using MicrOmega––Observation down to sub-mm scale structures
Identification of different compositional materials

3D image emphasizing the presence offew grains with specific composition:[Red] A largely OH-enriched grain© MicrOmega/IAS/CNES
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3. Scientific results
Distribution of hydrous material on RyuguOverview
The distribution of absorption from hydrous minerals (0.7µm band) wasobtained with the Optical Navigation Camera, ONC-T. Accuracy wasimproved by combining test data obtained before launch with the dataobtained after arrival at Ryugu. It was confirmed that the 0.7µm absorption isstrong in the low latitude area where the sample was collected.
Published in Icarus on May 15, 2021
online publication: January 29, 2021)
https://doi.org/10.1016/j.icarus.2021.114348
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3. Scientific results
Distribution of hydrous material on Ryugu
0.7µm absorption (approx. 3-4%)
Indicates the presence of hydrous
minerals. Disappears at hightemperatures.

Hydrous minerals (0.7µm) absorption
measured by the ONC-T before launch(Murchison meteorite). Modified fromKameda et al (2015)
2021/4/27

Using the 0.55µm, 0.7µm and 0.86µm out of the 7 filters available on the ONC-T,
the absorption was measured from the reflectance of 0.7µm wavelengths withrespect to 0.55µm and 0.86µm.
  

Blue in the figure on the right shows regions with strong absorption. Averageabsorption seemed to be detected at about 1%, with regional differences withabsorption as much as about 0.5% …???
Hayabusa2 reporter briefing93. Scientific results
Distribution of hydrous material on Ryugu
But a similar distribution was obtained in an entirely different
location! This suggested that the pattern was actually a characteristicof the instrument…
In order to detect 3 – 4% absorption, the required accuracy is about1%. The cause of this pattern was that the detector had an unevensensitivity of about 0.5%.

The sensitivity distribution (data needed to correct
unevenness in the sensitivity) was acquired before launchat room temperature, but the detector temperature when
Ryugu was observed was lower.
Although the test had revealed that the value of theaverage sensitivity of the entire image differed depending
on changes in temperature, the data was limited in range
due the test equipment and time restrictions.
It was found that the sensitivity distribution at room
temperature and that at low temperature on the detector
surface are slightly different.
This phenomenon was confirmed using a detector with thesame sensor as the ONC that had been prepared beforelaunch.

The research teamreferred to this as the“cat pattern”
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3. Scientific results
Distribution of hydrous material on Ryugu
Generate new sensitivity distribution data for low
temperatures using a large number of 288 images acquiredof Ryugu à re-correction
Correction accuracy for sensitivity unevenness wasimproved by around 2-3 times. The results confirmed a
regional different of 0.1 – 0.2% for 0.7µm absorption.

TD1TD2 Successful correction! (The cat pattern disappears).
0.7 µm absorption distribution is now visible.
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     


Low latitudes show slightly strong 0. 7µm absorption thanthe overall average. As the samples were obtained in thislow latitude region (black circles), it is possible that thesample could be collected at a location on Ryugu that
contains a large amount of hydrous minerals.

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3. Scientific results
Distribution of hydrous material on Ryugu
The results of this research
will be used when
considering thedevelopment andobservation plan for theMartian MoonseXploration Mission(MMX) cameras.
  

Although Ryugu is a black body that looks almost monochromatic,
there are regions that are slightly bluer and those that are more red. The
0.7 µm absorption tends to be stronger in the blue region.
(Upper left figure highlights blue and region regions.
à Blue regions are freshly exposed surface material and show
absorption of hydrous minerals that have not been exposed to hightemperatures.
àConsistent with previous results (Morota et al., 2020, etc)
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4. Scientific resultsPolarization observation with ground-based telescopes
Overview:

In September – December 2020, polarization observations of asteroid Ryugu were conducted at four facilities in Japan and overseas (Fig 4-1) and thedegree of polarization of Ryugu was discovered to be the highest recorded in history for an observation of a small Solar System body (Fig. 4-2). The
degree of polarization is thought to indicate the characteristic surface conditions such as mineral composition and grain size of the pebbles and sand on
the asteroid surface.
While Ryugu was comprehensibly observed from ground and space telescopes before the mission, and by the Hayabusa2 spacecraft, the degree ofpolarization had not been measured and there was no substitutable observation. The results from the observation was scientifically important as they canbe compared with the polarization of the sample returned by Hayabusa2. This is only the second case after the Moon to obtain the maximum value ofpolarization and a comparative sample from a celestial body. This result was published in The Astrophysical Journal Letters, April 20, 2021(DOI:10.3847/2041-8213/abee25)Region of maximum
value of the degreeof polarization

Fig 4-1: telescopes and instruments used in this observation (image credit for each in parentheses). From
left: Kanata Telescope + Hiroshima Optical and Near- InfraRed Camera HONIR (Hiroshima University),
Nayuta Telescope + Wide Field Grism Spectrograph WFGS2 (Hyodo Prefectural University), Pirka
Telescope + Visible Multispectral Imager MSI (Hokkaido University), Bohyunsan AstronomicalObservatory 1.8m telescope + Triple Range Imager and Polarimeter TRIPOL#3 (Seoul University)

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Fig 4-2: Asteroid phrase angle – polarization plot. Red circles indicate thedegree of polarization of Ryugu (credit: Kyoto University)

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4. Scientific results$
Polarization observation with ground-based telescopes
Background What is the degree of polarization
The light source is sunlight (wave vibrates in different directions = unpolarized)→ When this hits an object it is reflected or scattered and a strength bias is created in one
direction of vibration. The degree of this strength is the degree of polarization, which depends ontype, shape and size of the substance.

Asteroid

Polarized sunglasses utilize the fact that scattered light is polarized in one direction.
Image diagnostics put the degree of polarization to practical use in surveys such as ground disastermonitoring and land use (JAXA, NICT).

In(u cidn p en
ol t la r i ghi ze td)

 Purpose of measuring the degree of polarization for small Solar System bodies.
When the phase angle (Fig 4-3) changes, the degree of polarization also increases or decreases.
The aim is to identify the physical state of the surface layer from the characteristics (maximumvalue and trend) of the change in the degree of polarization

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Ph aObserver

se an gl e

SunScattering surface

Fig 4-3 #!#" !# #
 !" 

Objects with low degrees of polarization
Moon (observed in the latter half of the 20th century, measured in samples)
Asteroid Itokawa (destination of Hayabusa) etc.
Objects with high degree of polarization (>40%)
Asteroid 1998 KU 2 & Phaethon (planned destination of DESTINY +) etc
Due to lack of information about the surface layer, the cause of high degrees of polarization
cannot be identified.

Reflected light(polarized)

Ryugu, whose surface conditions have been wellinvestigated, was the optimal target for identifying whatkind of physical quantities the degree of polarization
depends on.

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4. Scientific results
Polarization observation with ground-based telescopes
Results of this research:
Asteroid Ryugu shows a high degree of polarization, with values up to 53% → highest value measured in thehistory of small Solar System bodies.
As this is the polarization of the entire body, it is thought that a special surface layer exists over a wide area.
Characteristics of the surface layer suggested by the degree of polarization
The contribution from submillimeter-sized particles was estimated through comparison with the degree ofpolarization in meteorites.
(1) Possibility that submillimeter-sized grains are present over most of the surface layer.
(2) Possible that submillimeter-sized grains are gathered to form larger rocks. The surface image captured byMASCOT (Fig 4–4) shows many rocks with a dark cauliflower-like structure, supporting this idea.

Fig 4-4
The image of the surface of Ryugu
observed by MASCOT(creditMASCOT/DLR/JAXA)

Future outlook:
By measuring the degree of polarization in the returned sample, the effects from the surface layer on the degree of polarization such as particle size and roughness
can be clarified. In addition, the surface structure of Ryugu—lost during the sample collection–will be reproduced.
If the link between the surface state and degree of polarization can be demonstrated so that the surface state of a celestial body can be estimated without relying onexploration, it will be possible to trace the history of many celestial body evolutions, and this will greatly contribute to the elucidation of the origin and evolutionof the Solar System.
Collaborators: Daisuke Kuroda (Kyodo University), Jooyeon Geem, Sunho Jin, Yoonsoo P. Bach, Jinguk Seo, Masateru Ishiguro (Seoul National University), Hiroshi Akitaya (Chiba Institute of Technology /Hiroshima University), Jun Takahashi, Aoi Kawakami, Miyako Tozukka (University of Hyogo), Koki Takahashi, Tomohiko Sekguchi (Hokkaido Kyoiku University), Hiroyuki Naito (Nayoto City
Astronomical Observatory), Kana Makino (Nayoro City University), Shuji Sato (Nagoya University), Hioroshi Sasago (Sasago Co., Ltd.), Koji Kawabata (Hiroshima University), Makoto Wataanbe (OkayamaUniversity of Science), Seiko Takagi, Kiyoshi Kuramoto (Hokkaido University), Makoto Yoshikawa, Sunao Hasegawa (JAXA)

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5. Spacecraft status• After the Earth return, the deployable camera control unit CAM-C failed.

– This is likely to have occurred from the deterioration due to radiation. CAM-C nolonger starts normally and image capture is no longer possible.
– The cause and possible recovery were investigated, but the project judged this to be afailure.
– This means it is no longer possible to shoot with CAM-H. CAM-H played the full rileof capturing the images at the moment of touchdown.

• Deterioration of spacecraft parts– Failures have occurred to the heater that maintains the temperature of the chemical
propulsion system thruster injection, but this has been recovered via a backup andlabor-saving operations will continue towards the destination celestial body.
– The spacecraft has exceeded its design lifespan and one of the goals of the Extended
Mission is the accumulate and experience the deterioration conditions. We willcontinue to make effective use of the valuable deep space navigation opportunities.

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5. Spacecraft status
CAM-H image captured on 2019.10.16
This was the last image captured by CAM-H
The results from CAM-H became one of themajor achievements that represented
Hayabusa2. The camera was installed using
donations from the public. We would like toexpress our sincere gratitude to everyone who
supported us and share this wonderful sense ofaccomplishment with you all.
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Reference Deployable camera control unit (CAM-C)
and related equipment
The deployable camera control unit (CAM-C) is the device that controls theDeployable Camera (DCAM3) and the sampler horn monitor camera (CAM-H). It is
installed inside the spacecraft. DCAM3 was separated at Ryugu on April 5, 2019.

Sampler horn monitor camera (small monitor camera headCAM-H) mounting location and field of view direction

Sampler horn monitor camera(small monitor camera head CAM-H) 2021/4/27

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18Reference Typical images captured by CAM-H
2014/12/5
Image when the sampler horn extended

2019/2/22
Image at the time of touchdown 1

2018/10/25
Touchdown 1 Rehearsal 3 TD1-R3

2019/7/11
Image at the time of touchdown 2 2021/4/27

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6. Future plans Operation schedule
2021/4 Continued regular operation
Ion engine operation schedule to start from the end of May(change from previously reported schedule) Open call for capsule exhibition tour
We are accepting applications from venues in different locations within Japan for thetraveling exhibition of the sample return capsule, scheduled to open after August.
Applications open4/27 TuesdayApplication deadline5/21FridayNotification of results6/18 (Friday)
For details, please see application guidelines.
 Press and media briefings
2021/5 TBD
Press briefing
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20Reference

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FTIR Fourier Transform Infrared Spectroscopy• wavelength 1 ~ 4µm
continuous spectroscopy• Spot diameter 1 ~ 6mm

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Hayabusa2 reporter briefing22MicrOmega (Near-Infrared Hyperspectral Microscope)
NIR spectroscopy for non-contaminated/non-destructive
description of return sample• wavelength range: 0.99-3.65 µm• spatial resolution: 22µm/pixel• observation area: 5x5mm• mounted on a small lander
MASCOT• AXA-CNES intl. collaboration• developed by IAS

refrigerator

Light source
HgCdTe detector wavelength scanHeatsource
AOTF

LEDwavelength λiNIR
monochromatorsample 2021/4/27

Frequency Fi

Opticalsystem

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cooled23