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Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

 Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Oral presentation

Analysis status of $$Sigma^+ p$$ scattering events in the J-PARC E40 experiment

Nanamura, Takuya; Ichikawa, Yudai; Hayakawa, Shuhei; Yoshida, Junya; Miwa, Koji*; Honda, Ryotaro*; Akazawa, Yuya*; Yamamoto, Takeshi

no journal, , 

Hyperon-nucleon scattering experiment is one of the powerful methods for studying YN interaction. However, it is difficult due to short lifetime of hyperon. $$Sigma N$$ scattering experiments were performed as KEK E251 and KEK E289 in order to measure the differential cross sections. In these experiments, statistics were limited to less than 100 events and differential cross section had too large statistical errors to restrict baryon-baryon interaction models. J-PARC E40 experiment aims for measuring cross sections of $$Sigma p$$ scatterings with high statistics ($$ sim $$10000 events) by overcoming difficulties of hyperon-nucleon scattering experiment. By using high rate ($$sim$$ 19M /spill) $$pi$$ beam and large acceptance spectrometer, we can produce and tag large amount of $$Sigma$$ beam. LH$$_2$$ target and surrounding detector system CATCH enable us to reconstruct reactions from two body kinematics. Our experimental group completed $$Sigma^-$$ data taking and about half of $$Sigma^+$$ data taking by 2019 Apr. Left data taking will be performed in the end of this fiscal year.

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