Search

Accepted: 2018-06-10, 資料番号: SA1180341000

In late 2018, the asteroid Ryugu was in the Sun’s shadow during the superior solar conjunction phase. As the Sun-Earth-Ryugu angle decreased to below 3°, the Hayabusa2 spacecraft experienced 21 days of planned blackout in the Earth-probe communication link. This was the first time a spacecraft had experienced solar conjunction while hovering around a minor body. For the safety of the spacecraft, a low energy transfer trajectory named Ayu was designed in the Hill reference frame to increase its altitude from 20 to 110 km. The trajectory was planned with the newly developed optNEAR tool and validated with real time data. This article shows the results of the conjunction operation, from planning to flight data.

The Tsushima Lapilli Tuff, the thickest tuff in the Taishu Group on Tsushima Island, underwent a thermal event after deposition, and has not previously yielded a reliable age because various ages have been reported. This study clarifies the eruption age and thermal history of the Tsushima Lapilli Tuff based on fission-track (FT) and U–Pb dating of zircon grains using laser ablation inductively coupled plasma mass spectrometry (ICP-LA-MS) and evaluates submarine volcanism during deposition of the Taishu Group in the southwestern Japan Sea, as well as volcanism change on Tsushima Island. This study revealed that thermal events caused rejuvenation in some single-grain FT ages after deposition in the Tsushima Group, and that the eruption age of the Tsushima Lapilli Tuff was 16.2 ± 0.7 Ma, the age of the largest submarine volcanism event in the Taishu Group in Tsushima Island was thus determined. On the basis of our previous studies, this age and tectonism strongly indicate that felsic submarine volcanism occurred between 18 and 16 Ma, accompanied by rapid subsidence, and the volcanism changed from felsic volcanism originating from melting of old continental crust by asthenospheric upwelling to mafic volcanism originating from small-scale lithospheric mantle upwelling from 13.6 Ma onward.

The Fukuzaki Limestone is a small limestone lens embedded in siliciclastic Taishu Group rocks on Tsushima Island in the southwestern Japan Sea. A fossil assemblage in this limestone consisting of the bivalve mollusc Bathymodiolus sp. (Bathymodiolinae) was previously inferred, on the basis of the limestone's isolated lenticular occurrence and the chemosynthetic nature of modern Bathymodiolinae, to rely on chemosynthetic production, but conclusive evidence was not provided. Carbon, nitrogen, oxygen, and sulfur isotope ratios in the limestone and its host rock mudstone were measured to clarify the paleoecology of the fossil assemblage and the formation environment of the limestone. The low δ13C (−39.8‰ to −31.7‰) and δ18O (−13.8‰ to −11.9‰) values of carbonate of the limestone lens strongly suggest that the limestone is composed of authigenic carbonate rock precipitated from bicarbonate derived from anaerobic oxidation of biogenic or thermogenic methane. The fossil assemblage in the limestone lens is consistent with a chemosynthesis-based animal assemblage harboring thioautotrophic (sulfur-oxidizing) symbionts, and the low δ13C and δ34S values of total organic carbon and sulfide sulfur, respectively, in the limestone lens and mud layers suggest that they reflect chemosynthetic production using hydrogen sulfide derived from anaerobic methane oxidation by microbes. Furthermore, the stratigraphic position of the lens in the upper part of the Lower Unit of the Taishu Group indicates that it was precipitated at a water depth >800 m (deeper than the lower middle bathyal zone). These findings indicate that a deep-sea basin locally supplied with methane had already formed in the southwestern Japan Sea by rapid subsidence during the opening stage of the Japan Sea (16–17 Ma).

This paper presents the planning, flight results and lessons learned of flyby guidance experiments of interplanetary micro-spacecraft PROCYON. PROCYON is the world's first interplanetary micro-spacecraft and was launched on 3rd December, 2014. Orbital control of interplanetary micro-spacecraft is challenging because of severe restriction and lower reliability on spacecraft system. For guidance strategy of PROCYON, we have introduced an innovative guidance strategy by two-stage stochastic programming for thrust-direction-constrained problem. Although the flight experiment has many difficulties especially on navigation, the flight result shows that we successfully demonstrate that PROCYON has been guided to the target point with objective guidance accuracy, which is within 100[km] on B-plane at 3,000,000[km] distance from the Earth. These results contributes the future flyby navigation and guidance for interplanetary micro-spacecraft, which has severe constraints and lower reliability on spacecraft system.

The Okinoshima Formation crops out on Okinoshima Island and comprises a thick sequence (> 200 m) of pyroclastic rocks and alternating beds of sandstone and mudstone. Because Okinoshima Island is located between Honshu and Tsushima Island, the Okinoshima Formation potentially provides an important record of volcanism during the opening of the Japan Sea in northwest Kyushu, as well as a record of the formation of the present Genkai Sea region. In consideration of the lack of previous geochronological work, dating (fission-track and U–Pb) of igneous zircons extracted from the Okinoshima Formation were undertaken and studied the clay mineral alteration in the pyroclastic material in order to reveal its thermal history. These data are used to constrain the age of the Okinoshima Formation and the present Genkai Sea region. Our results show that no thermal event has reset the fission-track age after deposition of the pyroclastic rocks, and that the Okinoshima Formation was deposited at 16.2 Ma. The present Genkai Sea region is a deep-sea basin, and its formation at 16.2 Ma was accompanied by submarine volcanism and rapid subsidence that marked the climactic stage of Japan Sea formation. After 16 Ma, the tectonic setting of the present Genkai Sea region changed from one of extension (related to the formation of the Japan Sea) to one of compression, with uplift occurring under the influence of the clockwise rotation of southwest Japan. Consequently, after 16 Ma the present Genkai Sea region became isolated from the forming processes of the Japan Sea.

The University of Arizona UAN Chapter engages middle school, high school, and undergraduate students through research-oriented outreach. Our fifth annual BECUR Conference held in February 2014 feat...

The world’s first solar sail IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) which is operated by Japan Aerospace Exploration Agency (JAXA) lost communication with the ground station due to the power short-age on December 24, 2011. In order to acquire IKAROS again after the power comes back, we immediately initiated to predict the attitude and orbit for the spacecraft.

資料番号: SA1160216000