Irradiation History of Itokawa Regolith Material Deduced from Noble Gases in the Hayabusa Samples

Nagao, Keisuke; Okazaki, Ryuji; Nakamura, Tomoki; Miura, Yayoi N.; Osawa, Takahiro; Bajo, K.; Matsuda, S.; Ebihara, Mitsuru; Ireland, Trevor; Kitajima, Fumio; Naraoka, Hiroshi; Noguchi, Takaaki; Tsuchiyama, A.; Yurimoto, H.; Zolensky, M. E.; Uesugi, Masayuki; Shirai, Kei; Abe, Masanao; Yada, Toru; Ishibashi, Yoshihiro; Fujimura, A.; Mukai, T.; Ueno, Munetaka; Okada, Tatsuaki; Yoshikawa, Makoto; Kawaguchi, Jun’ichiro

doi:10.1126/science.1207785

Cited by 132 publications

(104 citation statements)

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“…7 shows that the impactor flux on Itokawa particles is at least one order of magnitude higher than the interplanetary dust flux ( T = 10 4 yr) and comparable to the case of the Moon ( T = 10 2 to 10 3 yr). Considering that T = 10 2 to 10 3 yr is most likely the direct-exposure age according to the noble-gas analysis ( Nagao et al, 2011 ), we conclude that secondary ejecta impacts are probably the dominant cratering process in the submicrometersize range on Itokawa regolith particles, as well as on the lunar surface.…”

Section: Origin Of Submicrometer Cratersmentioning

confidence: 78%

“…In addition, microscopic meteoroid impacts contribute to changes in the optical properties, chemical composition, and structures of regolith surface material ( Noguchi et al, 2011;Harries and Langenhorst, 2014;Keller and Berger, 2014;Noguchi et al, 2014;Thompson et al, 2014;Bonal et al, 2015;Matsumoto et al, 2015;Harries et al, 2016;Matsumoto et al, 2016 ). In addition, regolith activity on Itokawaprobably driven by impact processes-has been identified based on grain motion ( Nagao et al, 2011;Matsumoto et al, 2016 ), fracturing ( Tsuchiyama et al, 2011;Langenhorst et al, 2014 ;Matsumoto et al, 2016 ), and abrasion ( Tsuchiyama et al, 2011 ). These previous studies have shown that Itokawa particles contain a record of the collective processes of regolith evolution on this small asteroid.…”

Section: Introductionmentioning

confidence: 93%

“…Previous investigations of the solar-flare track density showed that regolith particles spend up to of order 10 3 to 10 4 yr in the top few centimeters of Itokawa's surface ( Keller and Berger, 2014;Noguchi et al, 2014 ), which yields an upper limit to T . Measurements of solar-wind noble gases indicate that Itokawa particles were directly exposed to the space environment for 150-550 yr ( Nagao et al, 2011 ). Therefore, we assumed T in the range from 10 2 to 10 4 yr. We plotted F ( m ) as a function of m in Fig.…”

Section: Origin Of Submicrometer Cratersmentioning

confidence: 99%

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Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa

Matsumoto

Hasegawa

Nakao

et al. 2018

Icarus

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a b s t r a c tWe investigated impact crater structures on regolith particles from asteroid Itokawa using scanning electron microscopy. We observed the surfaces of 51 Itokawa particles, ranging from 15 μm to 240 μm in size. Craters with average diameters ranging from 10 nm to 2.8 μm were identified on 13 Itokawa particles larger than 80 μm. We examined the abundance, spatial distribution, and morphology of approximately 900 craters on six Itokawa particles. Craters with sizes in excess of 200 nm are widely dispersed, with spatial densities from 2.6 μm 2 to 4.5 μm 2 ; a fraction of the craters was locally concentrated with a density of 0.1 μm 2 . The fractal dimension of the cumulative crater diameters ranges from 1.3 to 2.3. Craters of several tens of nanometers in diameter exhibit pit and surrounding rim structures. Craters of more than 100 nm in diameter commonly have melted residue at their bottom. These morphologies are similar to those of submicrometer-sized craters on lunar regolith. We estimated the impactor flux on Itokawa regolith-forming craters, assuming that the craters were accumulated during direct exposure to the space environment for 10 2 to 10 4 yr. The range of impactor flux onto Itokawa particles is estimated to be at least one order of magnitude higher than the interplanetary dust flux and comparable to the secondary impact flux on the Moon. This indicates that secondary ejecta impacts are probably the dominant cratering process in the submicrometer range on Itokawa regolith particles, as well as on the lunar surface. We demonstrate that secondary submicrometer craters can be produced anywhere in centimeter-to meter-sized depressions on Itokawa's surface through primary interplanetary dust impacts. If the surface unevenness on centimeter to meter scales is a significant factor determining the abundance of submicrometer secondary cratering, the secondary impact flux could be independent of the overall shapes or sizes of celestial bodies, and the secondary impact flux could have similar values on Itokawa and the Moon.

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Section: Origin Of Submicrometer Cratersmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 93%

Section: Origin Of Submicrometer Cratersmentioning

confidence: 99%

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Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa

Matsumoto

Hasegawa

Nakao

et al. 2018

Icarus

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“…Asteroidal materials occurring as meteorites have been studied in detail. In particular, those recovered from the asteroid Itokawa by the Hayabusa spacecraft have been subjected to comprehensive studies (e.g., Nakamura et al 2011;Noguchi et al 2011Noguchi et al , 2014aNoguchi et al , 2014bNagao et al 2011;Tsuchiyama et al 2011;Yurimoto et al 2011;Nakamura et al 2012;Harries and Langenhorst 2014;Keller and Berger 2014;Langenhorst et al 2014;Mikouchi et al 2014;Thompson et al 2014;Takeda et al 2015). In contrast, it is difficult to obtain samples identified to be cometary in origin, with the exception of direct sampling by the Stardust mission that returned the dust samples from the short-period comet 81P/Wild 2 (Zolensky et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Mineralogy and noble gas isotopes of micrometeorites collected from Antarctic snow

et al. 2015

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We have investigated seven micrometeorites (MMs) from Antarctic snow collected in 2003 and 2010 by means of electron microscopy, X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy (TEM) observation, and noble-gas isotope analysis. Isotopic ratios of He and Ne indicate that the noble gases in these MMs are mostly of solar wind (SW). Based on the release patterns of SW 4 He, which should reflect the degree of heating during atmospheric entry, the seven MMs were classified into three types including two least heated, three moderately heated, and two severely heated MMs. The heating degrees are well correlated to their mineralogical features determined by TEM observation. One of the least heated MMs is composed of phyllosilicates, whereas the other consists of anhydrous minerals within which solar flare tracks were observed. The two severely heated MMs show clear evidence of atmospheric heating such as partial melt of the uppermost surface layer in one and abundant patches of dendritic magnetite and Si-rich glass within an olivine grain in the other. It is noteworthy that a moderately heated MM composed of a single crystal of olivine has a 3 He/

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“…In 2003, the Japanese Space Agency's (JAXA) Hayabusa mission was the first to focus on an asteroid with an aim to return a sample (Fujiwara et al, 2004). With only a basic scientific payload onboard Hayabusa, data gathered on the S-type asteroid Itokawa have nevertheless yielded incredible results (Nagao et al 2011, Tsuchiyama et al 2011) Ideas for visiting a Vtype NEO in a sample return mission are presented in the work of Duffard et al (2011).…”

Section: Mineralogy Of Basaltic Materials On the Minor Bodies Of Our Smentioning

confidence: 99%

Mineralogy of Basaltic Material on the Minor Bodies of Our Solar System

Duffárd¹

2012

An Introduction to the Study of Mineralogy

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Irradiation History of Itokawa Regolith Material Deduced from Noble Gases in the Hayabusa Samples

Cited by 132 publications

References 25 publications

Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa

Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa

Mineralogy and noble gas isotopes of micrometeorites collected from Antarctic snow

Mineralogy of Basaltic Material on the Minor Bodies of Our Solar System

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