Hayabusa2 Update

23rd NASA Small Bodies Assessment Group (SBAG) Meeting June 1, 2020 Makoto Yoshikawa, Yuichi Tsuda, and Hayabusa2 Project Team Summary

• After starting from Asteroid Ryugu in November 2019, the 1st ion engine operation was finished and now the 2nd ion engine operation is in progress. • The spacecraft operation is on schedule, and the Earth return is at the end of this year. • Scientific research is on going and many papers have been published.

2 Hayabusa2 : Outline of mission flow

Launch Earth swing-by Asteroid arrival MINERVA-II-1 December 3, 2014 September 21, 2018 December 3, 2015 June 27, 2018 MASCOT October 3, 2018

B Target Marker Release October 25, 2018 Asteroid departure E November 13, 2019

Earth return C nd A End of 2020 2 Touchdown Impactor April 5, 2019 st MI NE RVA-II-2 1 Touchdown finished → Target Marker Release Target Marker Release October 3, 2019 February 22, 2019 September 17, 2019 May 30, 2019 3 Target Markers 5 Beginning C Hayabusa2 Spacecraft B D A E Deployable Camera Ion Engine (DCAM3) X-band HGA X-band LGA Solar Array Panel X-band MGA RCS thrusters 12

Ka-band HGA ONC-T, ONC-W1

Star Trackers MASCOT Lander Near Infrared Spectrometer MI NE RVA-II Rovers Thermal Infrared Imager (TIR) (NIRS3) Reentry Capsule Size 1m1.6m1.25m (body) Small Carry-on Impactor (SCI) Mass 609kg (Wet) Target Markers 5 Sampler Horn LIDAR ONC-W2 MASCOT MI NE RVA-II-1 MI NE RVA-II-2

ONC-T LIDAR NIRS3 TIR by DLR and CNES II-1 : by JAXA MINERVA-II Team Science Instruments II-2 : by Tohoku Univ. & MINERVA-II consortium Small Lander and Rovers 4 Target Markers 5 Now C Hayabusa2 Spacecraft B D A E Deployable Camera Ion Engine (DCAM3) X-band HGA X-band LGA Solar Array Panel X-band MGA RCS thrusters 12

Ka-band HGA ONC-T, ONC-W1

Star Trackers MASCOT Lander Near Infrared Spectrometer MI NE RVA-II Rovers Thermal Infrared Imager (TIR) (NIRS3) Reentry Capsule Size 1m1.6m1.25m (body) Small Carry-on Impactor (SCI) Mass 609kg (Wet) Target Markers 5 1 Sampler Horn LIDAR ONC-W2 MASCOT MI NE RVA-II-1 MI NE RVA-II-2

ONC-T LIDAR NIRS3 TIR by DLR and CNES II-1 : by JAXA MINERVA-II Team Science Instruments II-2 : by Tohoku Univ. & MINERVA-II consortium Small Lander and Rovers 5 Current operation

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�� 2nd ion engine operation May 12, 2020 Sept. 2020 �� F �� 1st ion engine operation �� Dec 3, 2019 Feb. 20, 2020 H�� time881 hours �� ΔV100m/s �� remaining Xe 60% H�� 6 Recent Science Papers Highly porous nature of a primitive asteroid revealed by thermal imaging T. Okada et al. [16 March 2020: Nature volume 579, pages518–522(2020)]

An artificial impact on the asteroid 162173 Ryugu formed a crater in the gravity-dominated regime M. Arakawa et al. [03 Apr 2020: Science Vol. 368, Issue 6486, pp. 67-71]

Sample collection from asteroid 162173 Ryugu by Hayabusa2: implications for surface evolution T. Morota et al. [08 May 2020: Science Vol. 368, Issue 6491, pp. 654-659]

7 Highlights of Okada's Paper u We have acquired the first high-resolution thermal images of the entire asteroid for one rotation. u We discovered that the asteroid surface is covered with highly porous boulders and rock fragments rather than regolith. Exceptionally low temperature boulders called "Cold Spot" were also found. u We discovered that the temperature diurnal variation was small because of surface roughness. One-rotation global thermal images taken by TIR on Aug. 1, 2018 at the distance of about u We concluded that primitive small bodies 5km. including planetesimals may not have Image credit : JAXA, Rikkyo University, Ashikaga University, Chiba Institute of Technology, University of Aizu, Hokkaido University of experienced substantial compaction. Ryugu could Education, Hokkaido Kitami Hokuto High School, AIST, National Institute for Environmental Studies, University of Tokyo, DLR, Max Planck Society be between fluffy dust to dense celestial bodies. for the Advancement of Science, Stirling University, OCA. 8 A Formation Scenario of Ryugu – A Porous Planetesimal Hypothesis by Okada et al.

Extended Data Fig. 4. A formation scenario of Ryugu from a porous parent body. (1) Formation began with fluffy dust in the solar nebula. (2) Porous planetesimals were formed by accretion of dust or pebbles. (3) The parent body of Ryugu might have remained porous owing to a low degree of consolidation. A clear boundary of the inner core is illustrated but a gradual increase of consolidation by depth might be expected. (4) Impact fragmentation of the parent body occurred. Some large fragments are the boulders on Ryugu. (5) Part of fragments re-accreted to form Ryugu, with porous boulders and sediments on the surface, and some dense boulders originating from the inner core. (6) Re-shaping caused by a change in rotation rate to form a double-top-shape.

9 Highlights of Arakawa's Paper

We understood the crater formation process in the Hayabusa2 impactor experiment. Crater formed on Ryugu is about 7 times larger than that formed on the Earth. Ryugu’s surface age is young of order 107 years

l The SCI crater can be simulated as a crater forming in sand that lacks strength under microgravity 10-5G conditions. l The SCI crater revealed the surface of Ryugu Comparison of images captured before the SCI operation (March 22, 2019) and after the has nearly no strength. collision (April 25, 2019): animation

Arakawa et al., 2020 10 Before & after the collision with DCAM3 by Arakawa et al. • Impact point: 7.9N, 301.3E. • SCI projectile impacted obliquely at an angle of 60to the surface of Ryugu.

185 s before the impact

60º SCI body

3s after the impact

A B Arakawa et al., 2020

11 SCI crater shape by Arakawa et al. • Diameter14.50.8m DEM: Digital Elevation Map – Crater diameter at 0m height. • Rim diameter17.60.7m – Distance between rim tops • Pit diameter about 3mdepth 60cm – 140 – 670 Pa layer at bottom • Rim height40cm – Rim consisting of ejecta deposits • Crater bottom depth – Depth from height 0m1.7m • Depth from rim top to pit bottom: – 2.7m Rim diameter Rim height diameter Arakawa et al., 2020 pit 12 Ejecta curtain by Arakawa et al.

• Ejecta generated in the collision initially spray northward. • Crater formation, excavation and deposition process, lasts for 500 seconds. • No separation between the ejecta curtain and ground surface is observed. • For the first 200 seconds, the crater appears to be growing. After this, the ejecta deposition is occurring.

Arakawa et al., 2020

13 Ejecta curtain (animation)by Arakawa et al.

Ejecta curtain growth and deposition. Animation created using images from 185 seconds before the SCI collision and 3s, 5s, 36s, 100s, 192s, 396s and 489s after collision. Arakawa et al., 2020

14 Highlights of Morota's Paper

• The 1st touchdown raised 1m-sized rocks and a lot of reddish-dark particles. • The reddish-dark particles were created by the alteration of the surface of Ryugu from the heating or space weathering by the Sun. • Surface alteration occurred during a short period in the past à Ryugu was once on a temporary orbit that approached the Sun. • Both the altered and unaltered materials are expected to have been collected. Movie of images taken with the ONC-W1 at the time of the first touchdown. (Movie) ©Morota et al., 2020 15 Color change before and after touchdown by Morota et al.

Ø After touchdown, fine particles were deposited over an area with diameter 10m.

Ø The area around the touchdown point changed to reddish-dark compared to prior to touchdown.

Ø The fine particles were the reddish-dark material.

Figure is partially modified from Morota et al. (2020). Dates and times on the figure are in Coordinated Universal Time (UTC) 16 Global color distributionrelation with craters Figure is partially modified from Morota et al. (2020). by Morota et al. (1)

Surface color change (2) (reddish)

Blue crater

Red crater (3) Ø The lower (older) craters tend to be red, while the upper (younger) craters tend to be blue. Ø Red crater: A crater formed before the surface reddened. Ø Blue crater: A crater formed after the surface reddened. Ø Latitude dependence of the red-blue distribution à surface reddening caused by heating or weathering by the Sun. Ø Bimodal distribution of red and blue craters à surface reddening occurred over a short period of time. 2020/5/8 17 by Morota et al. Ryugu evolution history

Mission goal Minimum success Full success Extra success Science goal Provide new insights on the Obtain new findings on mineral- Integrate astronomical & microscale Achieved Investigate the material surface material of C-type water-organic interactions by the information to create new scientific characteristics of C-type asteroids. asteroids by observations in the initial analysis of the collected results regarding materials for Earth, Awaiting achievement In particular, clarify the interaction vicinity of the asteroid. samples. sea and life. confirmation between minerals, water and organic matter. Science goal Provide insights on the internal Obtain new knowledge on the Present scientific results on asteroid Investigate the formation process structure of the asteroid by internal structure and subsurface formation based on new findings of asteroids by direct exploration of observations in the vicinity of material of the asteroid by regarding the collision destruction & the asteroid’s reaccumulation the asteroid. observing the phenomena caused by reaccumulation process. process, internal structure and collisions with an impacting body. New scientific results from the subsurface material. exploration robots on the surface environment of asteroids. Engineering goal Rendezvous with a target orbit Drop the exploration robot to the Improve robustness, accuracy and using ion engines for deep space asteroid surface. N/A operability of the new technology propulsion. Take a sample of the asteroid implemented in Hayabusa, and surface. mature it as a technology. Collect the re-entry capsule on Current Earth.

Engineering goal Construct a system to allow an Make the impact device collide in a Collect a sample of asteroid aim Demonstrate impact object impact device to collide with specified area. subsurface material exposed during colliding with a celestial body. the target object and perform the collision. that collision with the asteroid.

19 Now (June 2020) Hayabusa2 Mission Success Criteria

Engineering goal Construct a system to allow an Make the impact device collide in a Collect a sample of asteroid Demonstrate impact object impact device to collide with specified area. subsurface material exposed during colliding with a celestial body. the target object and perform the collision. that collision with the asteroid.