Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu—A spinning top–shaped rubble pile

Watanabe, S.; Hirabayashi, Masatoshi; Hirata, Naru; Hirata, Naoyuki; Noguchi, Rina; Shimaki, Y.; Ikeda, Hitoshi; Tatsumi, Eri; Yoshikawa, Makoto; Kikuchi, Shota; Yabuta, Hikaru; Nakamura, Tomoki; Tachibana, Shogo; Ishihara, Yoshiaki; Morota, T.; Kitazato, K.; Sakatani, Naoya; Matsumoto, Koji; Wada, Koji; Senshu, Hiroki; Honda, Chikatoshi; Michikami, Tatsuhiro; Takeuchi, Hiroshi; Kouyama, T.; Honda, Rie; Kameda, Shingo; Fuse, Tetsuharu; Miyamoto, H.; Komatsu, G.; Sugita, Seiji; Okada, T.; Namiki, Noriyuki; Arakawa, Masahiko; Ishiguro, Masateru; Okazaki, Ryuji; Gaskell, R. W.; Palmer, E. E.; Barnouin, Olivier S.; Michel, Patrick; French, A. S.; McMahon, Jay W.; Scheeres, Daniel J.; Abell, P. A.; Yamamoto, Yukio; Tanaka, Satoshi; Shirai, Kei; Matsuoka, Moe; Yamada, Manabu; Yokota, Yasuhiro; Suzuki, Hidehiko; Yoshioka, Kazuo; Cho, Yuichiro; Nishikawa, Naoki; Sugiyama, Tomoshi; Kikuchi, Hiroshi; Hemmi, Ryodo; Yamaguchi, Tomohiro; Ogawa, Naoko; Ono, Go; Mimasu, Yuya; Yoshikawa, K.; Takahashi, T.; Takei, Yuto; Fujii, Atsushi; Hirose, Chikako; Iwata, T.; Hayakawa, Masahiko; Hosoda, Saichi; Mori, Osamu; Sawada, Hirotaka; Shimada, Takanobu; Soldini, Stefania; Yano, Hajime; Tsukizaki, Ryudo; Ozaki, Masanobu; Iijima, Y.; Ogawa, Kazunori; Fujimoto, M.; Ho, Tra‐Mi; Moussi‐Soffys, Aurélie; Jaumann, R.; Bibring, Jean‐Pierre; Krause, Christian; Terui, Fuyuto; Saiki, Takanao; Nakazawa, Shozo; Tsuda, Yuichi

doi:10.1126/science.aav8032

Cited by 452 publications

(383 citation statements)

References 51 publications

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“…In the present study, we will focus on the magnetization characteristics of Ryugu and its material. Ryugu is categorized as a Cb‐type asteroid (Watanabe et al, ). The Hayabusa2 observations show very low albedo (geometric albedo

\sim

4.5 and reflectance

\sim

1.88% at 0.55

normalμ

m) and three main types of boulders of the surface (Sugita et al, ).…”

Section: Introductionmentioning

confidence: 99%

Magnetic Properties of Asteroid (162173) Ryugu

et al. 2020

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Observations of the magnetization state of asteroids indicate diverse properties. Values between 1.9 × 10 −6 Am 2 /kg (Eros) and 10 −2 Am 2 /kg (Braille) have been reported. A more detailed understanding of asteroidal magnetic properties allows far-reaching conclusions of the magnetization mechanism as well as the strength of the magnetic field of the solar system regions the asteroid formed in. The Hayabusa2 mission with its lander Mobile Asteroid Surface Scout is equipped with a magnetometer experiment, MasMag. MasMag is a state-of-the-art three-axis fluxgate magnetometer, successfully operated also on Philae, the Rosetta mission lander. MasMag has enabled, after Eros for the second time ever, to determine the magnetic field of an asteroid during descent and on-surface operations. The new observations show that Ryugu, a low-albedo C-type asteroid, has no detectable global magnetization, and any local magnetization is either small (< 10 −6 Am 2 /kg) or on very small (subcentimeter) scales. This implies, for example, that energetic solar wind particles could reach and alter the surface unimpeded by strong asteroidal magnetic fields, such as minimagnetospheres in case of the Moon.Plain Language Summary Magnetic measurements in space near and on solar system bodies such as asteroids can provide important information about their formation history and their material properties. Hayabusa2, a Japanese mission, visited asteroid Ryugu, a type of asteroid (carbon rich) not visited before. Ryugu is a rubble pile, that is, an agglomeration of rocks and boulders. It is not expected to have any global magnetic field, but it can be magnetized on smaller scales (boulders or pebbles). Hayabusa2 carried therefore a small lander called Mobile Asteroid Surface Scout equipped also with an instrument for magnetic field measurement (magnetometer). In this study, we present observations from the magnetometer that were collected during Mobile Asteroid Surface Scout's descent and landing on the surface of Ryugu. The magnetic measurements show that Ryugu is not magnetized on boulder (greater than centimeter) scales. This gives us indication on its origin and evolution. In particular, it shows that Ryugu and the bodies it was created from did not possess any magnetic field generation mechanism and that they were not created in an environment with strong background magnetic field. The results are important inputs for theories about the solar system evolution that work with magnetic field as one of the drivers for dust accretion and planetary formation.

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\sim

4.5 and reflectance

\sim

1.88% at 0.55

normalμ

m) and three main types of boulders of the surface (Sugita et al, ).…”

Section: Introductionmentioning

confidence: 99%

Magnetic Properties of Asteroid (162173) Ryugu

et al. 2020

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“…In December 2018 the OSIRIS-REx spacecraft arrived at asteroid (101955) Bennu and began to characterise that body Lauretta et al (2019). The overall bulk density of the asteroid was found to be 1190 kg/m 3 , the same value as Ryugu, and both of their macro-porosities were estimated to be up to 50%, consistent with being a 'rubble pile ' Scheeres et al (2019); Watanabe et al (2019). The surface of both Bennu and Ryugu were seen to be uniformly covered by boulders across a large size distribution, with very few regions covered by finer regolith Walsh et al (2019); Sugita et al (2019).…”

Section: Discussion and Prospectivementioning

confidence: 98%

Small Solar System Bodies as granular media

Hestroffer

Sánchez

Staron

et al. 2019

Astron Astrophys Rev

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“…Finally, We assumed that Phaethon currently has a top shape having Bennus oblateness, = 0.889, by following Taylor et al (2019). To check if this setting is consistent with other top-shaped asteroids, we consider six top-shaped near-earth asteroids: Ryugu (Watanabe et al 2019), 1994KW4 (Ostro et al 2006EV5 (Busch et al 2011), 1994CC (Brozović et al 2011), 2001SN263 (Becker et al 2015, and 2000 DP107 (Naidu et al 2015). We find the range of to be 0.873 0.968, and thus Bennus is within this range.…”

Section: Possible Source Of the Geminid Meteor Streammentioning

confidence: 99%

“…The equivalent diameter of this asteroid was estimated to be 6 km in diameter. The examples of top-shaped asteroids are OSIRIS-RExs target (101955) Bennu (Lauretta et al 2019) and Hayabusa2s target (162173) Ryugu (Watanabe et al 2019;Sugita et al 2019;Kitazato et al 2019). Phaethon is currently spinning at a rotation period of 3.60 hr (Taylor et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Mass-shedding Activities of Asteroid (3200) Phaethon Enhanced by Its Rotation

Nakano

Hirabayashi

2020

ApJL

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Asteroid (3200) Phaethon, a B-type asteroid, has been active during its perihelion passages. This asteroid is considered to be a source of the Geminid meteor stream. It is reported that this asteroid is spinning at a rotation period of 3.60 hr and has a top shape (an oblate body with an equatorial ridge) with a mean equatorial diameter of 6.25 km. Here, we report that Phaethon's rotation state may be close to or above its critical rotation period when the bulk density is 0.5 − 1.5 g/cm 3 (a typical bulk density of a B-type asteroid). We found that in this condition, the structure of Phaethon is sensitive to failure unless the cohesive strength is ∼50 P a − ∼260 P a. This result implies that if there are some surface processes driven by, for example, thermal waves, large-scaled deformation may happen and cause mass shedding. From this interpretation, we propose the processes that produced the Geminid meteor stream in the past and dust tails recently. Phaethon initially rotated at a spin period shorter than the current period. The magnitude of structural deformation at this stage was higher than the present spin condition, and a large mass shedding event, i.e., the Geminid meteor stream, occurred. After this deformation process, the body became more oblate, and its spin slowed down. At this point, while the spin was high enough for the body to have mass shedding events, the magnitude of these events became small.

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Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu—A spinning top–shaped rubble pile

Cited by 452 publications

References 51 publications

Magnetic Properties of Asteroid (162173) Ryugu

Magnetic Properties of Asteroid (162173) Ryugu

Small Solar System Bodies as granular media

Mass-shedding Activities of Asteroid (3200) Phaethon Enhanced by Its Rotation

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