A dehydrated space-weathered skin cloaking the hydrated interior of Ryugu.

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (-OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.

Biofinder detects biological remains in Green River fish fossils from Eocene epoch at video speed.

The "Search for life", which may be extinct or extant on other planetary bodies is one of the major goals of NASA planetary exploration missions. Finding such evidence of biological residue in a vast planetary landscape is an enormous challenge. We have developed a highly sensitive instrument, the "Compact Color Biofinder", which can locate minute amounts of biological material in a large area at video speed from a standoff distance. Here we demonstrate the efficacy of the Biofinder to detect fossils that still possess strong bio-fluorescence signals from a collection of samples. Fluorescence images taken by the Biofinder instrument show that all Knightia spp. fish fossils analysed from the Green River formation (Eocene, 56.0-33.9 Mya) still contain considerable amounts of biological residues. The biofluorescence images support the fact that organic matter has been well preserved in the Green River formation, and thus, not diagenetically replaced (replaced by minerals) over such a significant timescale. We further corroborated results from the Biofinder fluorescence imagery through Raman and attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopies, scanning electron microscopy, energy dispersive X-ray spectroscopy (SEM-EDS), and fluorescence lifetime imaging microscopy (FLIM). Our findings confirm once more that biological residues can survive millions of years, and that using biofluorescence imaging effectively detects these trace residues in real time. We anticipate that fluorescence imaging will be critical in future NASA missions to detect organics and the existence of life on other planetary bodies.

Combined Focused Ion Beam-Ultramicrotomy Method for TEM Specimen Preparation of Porous Fine-Grained Materials.

A new transmission electron microscopy (TEM) specimen preparation method that utilizes a combination of focused ion beam (FIB) methods and ultramicrotomy is demonstrated. This combined method retains the benefit of site-specific sampling by FIB but eliminates ion beam-induced damage except at specimen edges and allows recovery of many consecutive sections. It is best applied to porous and/or fine-grained materials that are amenable to ultramicrotomy but are located in bulk samples that are not. The method is ideal for unique samples from which every specimen is precious, and we demonstrate its utility on fine-grained material from the one-of-a-kind Paris meteorite. Compared with a specimen prepared by conventional FIB methods, the final sections are uniformly thin and free from re-deposition and curtaining artifacts common in FIB specimens prepared from porous, heterogeneous samples.

Improved high temperature radiation damage tolerance in a three-phase ceramic with heterointerfaces.

Radiation damage tolerance for a variety of ceramics at high temperatures depends on the material's resistance to nucleation and growth of extended defects. Such processes are prevalent in ceramics employed for space, nuclear fission/fusion and nuclear waste environments. This report shows that random heterointerfaces in materials with sub-micron grains can act as highly efficient sinks for point defects compared to grain boundaries in single-phase materials. The concentration of dislocation loops in a radiation damage-prone phase (Al2O3) is significantly reduced when Al2O3 is a component of a composite system as opposed to a single-phase system. These results present a novel method for designing exceptionally radiation damage tolerant ceramics at high temperatures with a stable grain size, without requiring extensive interfacial engineering or production of nanocrystalline materials.