Highly porous nature of a primitive asteroid revealed by thermal imaging.

Carbonaceous (C-type) asteroids1 are relics of the early Solar System that have preserved primitive materials since their formation approximately 4.6 billion years ago. They are probably analogues of carbonaceous chondrites2,3 and are essential for understanding planetary formation processes. However, their physical properties remain poorly known because carbonaceous chondrite meteoroids tend not to survive entry to Earth's atmosphere. Here we report on global one-rotation thermographic images of the C-type asteroid 162173 Ryugu, taken by the thermal infrared imager (TIR)4 onboard the spacecraft Hayabusa25, indicating that the asteroid's boulders and their surroundings have similar temperatures, with a derived thermal inertia of about 300 J m-2 s-0.5 K-1 (300 tiu). Contrary to predictions that the surface consists of regolith and dense boulders, this low thermal inertia suggests that the boulders are more porous than typical carbonaceous chondrites6 and that their surroundings are covered with porous fragments more than 10 centimetres in diameter. Close-up thermal images confirm the presence of such porous fragments and the flat diurnal temperature profiles suggest a strong surface roughness effect7,8. We also observed in the close-up thermal images boulders that are colder during the day, with thermal inertia exceeding 600 tiu, corresponding to dense boulders similar to typical carbonaceous chondrites6. These results constrain the formation history of Ryugu: the asteroid must be a rubble pile formed from impact fragments of a parent body with microporosity9 of approximately 30 to 50 per cent that experienced a low degree of consolidation. The dense boulders might have originated from the consolidated innermost region or they may have an exogenic origin. This high-porosity asteroid may link cosmic fluffy dust to dense celestial bodies10.

Classification of volcanic ash particles using a convolutional neural network and probability.

Analyses of volcanic ash are typically performed either by qualitatively classifying ash particles by eye or by quantitatively parameterizing its shape and texture. While complex shapes can be classified through qualitative analyses, the results are subjective due to the difficulty of categorizing complex shapes into a single class. Although quantitative analyses are objective, selection of shape parameters is required. Here, we applied a convolutional neural network (CNN) for the classification of volcanic ash. First, we defined four basal particle shapes (blocky, vesicular, elongated, rounded) generated by different eruption mechanisms (e.g., brittle fragmentation), and then trained the CNN using particles composed of only one basal shape. The CNN could recognize the basal shapes with over 90% accuracy. Using the trained network, we classified ash particles composed of multiple basal shapes based on the output of the network, which can be interpreted as a mixing ratio of the four basal shapes. Clustering of samples by the averaged probabilities and the intensity is consistent with the eruption type. The mixing ratio output by the CNN can be used to quantitatively classify complex shapes in nature without categorizing forcibly and without the need for shape parameters, which may lead to a new taxonomy.

Folic Acid Deficiency Does Not Adversely Affect Oocyte Meiosis in Mice.

Spindle defect and chromosome misalignment occuring in oocyte meiosis induce nondisjunction. Nondisjunction causes Down syndrome, also known as trisomy 21. Folic acid (FA) is an essential nutrient composition for fetal growth and development. It has been reported that FA nutritional status is associated with the risk of Down syndrome. However, to our knowledge, little is known about the effect of FA deficiency on abnormal oocytes (spindle defects, chromosome misalignments and immature oocyte) in vivo. In the present study, we investigate the effects of FA deficiency on oocyte meiosis in female mice. In order to induce FA deficiency in mice, female Crl:CD1 mice were fed a FA-free diet for 58 d. The diet also contained an antibiotic which has functions on limiting FA formation by intestinal microorganisms. The level of FA deficiency was determined by measuring the concentration of FA in the liver, hemocyte, uterus, ovary, and urine. FA concentrations in these samples from the FA-deficient group were 50-90% lower. Despite this, the frequency of abnormal oocytes was no different between the FA-deficient and control groups (20.0% vs 14.6%). According to the past research, FA transporter was strongly expressed in oocytes. Hence, it is possible that FA-free diets may not affect the concentration of oocyte FA in mice. To sum up these data, our study concluded that FA deficiency did not adversely affect oocyte meiosis.