ABSTRACT
The Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu's boulders, and shapes from quasi-spherical to flattened. The samples were returned to Earth on 6 December 2020. We describe the morphology of >5 grams of returned pebbles and sand. Their diverse color, shape, and structure are consistent with the observed materials of Ryugu; we conclude that they are a representative sample of the asteroid.
ABSTRACT
The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu's shape, mass, and geomorphology. Ryugu has an oblate "spinning top" shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu's shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.
ABSTRACT
The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu's surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.
ABSTRACT
In vitro proliferative responses of T lymphocytes in the peritoneal exudate cells of C3H/HeN(Iak) mice immunized with horse red blood cells (HRBC) were examined by determining the uptake of tritiated thymidine [( 3H]TdR) into the cells. Although the cells showed a basal proliferative response in the absence of antigen, addition of specific antigen increased the response sharply. Both the basal response and that stimulated by antigen disappeared if the cells had been previously treated with complement and anti-Iak antibody (AIak), anti-MAC-1 antibody (AMAC-1) or anti-Thy-1 antibody, but not anti-Ig antibody. Adding macrophages prepared from the peritoneal exudate cells of normal mice to AMAC-1-treated T-cell (i.e. Iak+ plus Iak- T-cell) cultures restored both of the responses, while adding them to AIak-treated T cells (i.e. Iak- T cells) only restored the antigen-specific response. These findings indicate that the basal proliferation is due to or dependent on the proliferation of Iak+ T cells, while the antigen-specific response is mainly due to Iak- T cells. Furthermore, interleukin (IL)-2 production was also examined. Immune T cells produced some IL-2 in the absence of antigen. The production by AMAC-1- or AIak-treated cells was impaired, but adding macrophages to the AMAC-1-treated cell cultures restored production. This result also suggests that the mode of IL-2 production by the Iak+ and Iak- cells is different. Proliferative responses of AMAC-1- or AIak-treated T cells to IL-2 were also examined. The AIak-treated cells dose-dependently responded to IL-2, while the response of Iak+ cells, which could be estimated by subtracting the response of AIak-treated cells from that of AMAC-1-treated cells, did not depend on the doses. These results indicate that in the immune peritoneal exudate the Iak+ T cells are functionally different from Iak- T cells.