Images from the surface of asteroid Ryugu show rocks similar to carbonaceous chondrite meteorites.

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.

The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes.

The near-Earth carbonaceous asteroid 162173 Ryugu is thought to have been produced from a parent body that contained water ice and organic molecules. The Hayabusa2 spacecraft has obtained global multicolor images of Ryugu. Geomorphological features present include a circum-equatorial ridge, east-west dichotomy, high boulder abundances across the entire surface, and impact craters. Age estimates from the craters indicate a resurfacing age of [Formula: see text] years for the top 1-meter layer. Ryugu is among the darkest known bodies in the Solar System. The high abundance and spectral properties of boulders are consistent with moderately dehydrated materials, analogous to thermally metamorphosed meteorites found on Earth. The general uniformity in color across Ryugu's surface supports partial dehydration due to internal heating of the asteroid's parent body.

COMETARY SCIENCE. The structure of the regolith on 67P/Churyumov-Gerasimenko from ROLIS descent imaging.

The structure of the upper layer of a comet is a product of its surface activity. The Rosetta Lander Imaging System (ROLIS) on board Philae acquired close-range images of the Agilkia site during its descent onto comet 67P/Churyumov-Gerasimenko. These images reveal a photometrically uniform surface covered by regolith composed of debris and blocks ranging in size from centimeters to 5 meters. At the highest resolution of 1 centimeter per pixel, the surface appears granular, with no apparent deposits of unresolved sand-sized particles. The thickness of the regolith varies across the imaged field from 0 to 1 to 2 meters. The presence of aeolian-like features resembling wind tails hints at regolith mobilization and erosion processes. Modeling suggests that abrasion driven by airfall-induced particle "splashing" is responsible for the observed formations.

Dark material on Vesta from the infall of carbonaceous volatile-rich material.

Localized dark and bright materials, often with extremely different albedos, were recently found on Vesta's surface. The range of albedos is among the largest observed on Solar System rocky bodies. These dark materials, often associated with craters, appear in ejecta and crater walls, and their pyroxene absorption strengths are correlated with material brightness. It was tentatively suggested that the dark material on Vesta could be either exogenic, from carbon-rich, low-velocity impactors, or endogenic, from freshly exposed mafic material or impact melt, created or exposed by impacts. Here we report Vesta spectra and images and use them to derive and interpret the properties of the 'pure' dark and bright materials. We argue that the dark material is mainly from infall of hydrated carbonaceous material (like that found in a major class of meteorites and some comet surfaces), whereas the bright material is the uncontaminated indigenous Vesta basaltic soil. Dark material from low-albedo impactors is diffused over time through the Vestan regolith by impact mixing, creating broader, diffuse darker regions and finally Vesta's background surface material. This is consistent with howardite-eucrite-diogenite meteorites coming from Vesta.

E-type asteroid (2867) Steins as imaged by OSIRIS on board Rosetta.

The European Space Agency's Rosetta mission encountered the main-belt asteroid (2867) Steins while on its way to rendezvous with comet 67P/Churyumov-Gerasimenko. Images taken with the OSIRIS (optical, spectroscopic, and infrared remote( )imaging system) cameras on board Rosetta show that Steins is an oblate body with an effective spherical diameter of 5.3 kilometers. Its surface does not show color variations. The morphology of Steins is dominated by linear faults and a large 2.1-kilometer-diameter crater near its south pole. Crater counts reveal a distinct lack of small craters. Steins is not solid rock but a rubble pile and has a conical appearance that is probably the result of reshaping due to Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) spin-up. The OSIRIS images constitute direct evidence for the YORP effect on a main-belt asteroid.

Human polymer-based cartilage grafts for the regeneration of articular cartilage defects.

The use of autologous chondrocyte implantation (ACI) and its further development combining autologous chondrocytes with bioresorbable matrices may represent a promising new technology for cartilage regeneration in orthopaedic research. Aim of our study was to evaluate the applicability of a resorbable three-dimensional polymer of pure polyglycolic acid (PGA) for the use in human cartilage tissue engineering under autologous conditions. Adult human chondrocytes were expanded in vitro using human serum and were rearranged three-dimensionally in human fibrin and PGA. The capacity of dedifferentiated chondrocytes to re-differentiate was evaluated after two weeks of tissue culture in vitro and after subcutaneous transplantation into nude mice by propidium iodide/fluorescein diacetate (PI/FDA) staining, scanning electron microscopy (SEM), gene expression analysis of typical chondrocyte marker genes and histological staining of proteoglycans and type II collagen. PI/FDA staining and SEM documented that vital human chondrocytes are evenly distributed within the polymer-based cartilage tissue engineering graft. The induction of the typical chondrocyte marker genes including cartilage oligomeric matrix protein (COMP) and cartilage link protein after two weeks of tissue culture indicates the initiation of chondrocyte re-differentiation by three-dimensional assembly in fibrin and PGA. Histological analysis of human cartilage tissue engineering grafts after 6 weeks of subcutaneous transplantation demonstrates the development of the graft towards hyaline cartilage with formation of a cartilaginous matrix comprising type II collagen and proteoglycan. These results suggest that human polymer-based cartilage tissue engineering grafts made of human chondrocytes, human fibrin and PGA are clinically suited for the regeneration of articular cartilage defects.

Rain, winds and haze during the Huygens probe's descent to Titan's surface.

The irreversible conversion of methane into higher hydrocarbons in Titan's stratosphere implies a surface or subsurface methane reservoir. Recent measurements from the cameras aboard the Cassini orbiter fail to see a global reservoir, but the methane and smog in Titan's atmosphere impedes the search for hydrocarbons on the surface. Here we report spectra and high-resolution images obtained by the Huygens Probe Descent Imager/Spectral Radiometer instrument in Titan's atmosphere. Although these images do not show liquid hydrocarbon pools on the surface, they do reveal the traces of once flowing liquid. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands. Images taken after landing are of a dry riverbed. The infrared reflectance spectrum measured for the surface is unlike any other in the Solar System; there is a red slope in the optical range that is consistent with an organic material such as tholins, and absorption from water ice is seen. However, a blue slope in the near-infrared suggests another, unknown constituent. The number density of haze particles increases by a factor of just a few from an altitude of 150 km to the surface, with no clear space below the tropopause. The methane relative humidity near the surface is 50 per cent.