The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

Filtration efficiency (FE), differential pressure (ΔP), quality factor (QF), and construction parameters were measured for 32 cloth materials (14 cotton, 1 wool, 9 synthetic, 4 synthetic blends, and 4 synthetic/cotton blends) used in cloth masks intended for protection from the SARS-CoV-2 virus (diameter 100 ± 10 nm). Seven polypropylene-based fiber filter materials were also measured including surgical masks and N95 respirators. Additional measurements were performed on both multilayered and mixed-material samples of natural, synthetic, or natural-synthetic blends to mimic cloth mask construction methods. Materials were microimaged and tested against size selected NaCl aerosol with particle mobility diameters between 50 and 825 nm. Three of the top five best performing samples were woven 100% cotton with high to moderate yarn counts, and the other two were woven synthetics of moderate yarn counts. In contrast to recently published studies, samples utilizing mixed materials did not exhibit a significant difference in the measured FE when compared to the product of the individual FE for the components. The FE and ΔP increased monotonically with the number of cloth layers for a lightweight flannel, suggesting that multilayered cloth masks may offer increased protection from nanometer-sized aerosol with a maximum FE dictated by breathability (i.e., ΔP).

The source and nature of carbon on Mars have been a subject of intense speculation. We report the results of confocal Raman imaging spectroscopy on 11 martian meteorites, spanning about 4.2 billion years of martian history. Ten of the meteorites contain abiotic macromolecular carbon (MMC) phases detected in association with small oxide grains included within high-temperature minerals. Polycyclic aromatic hydrocarbons were detected along with MMC phases in Dar al Gani 476. The association of organic carbon within magmatic minerals indicates that martian magmas favored precipitation of reduced carbon species during crystallization. The ubiquitous distribution of abiotic organic carbon in martian igneous rocks is important for understanding the martian carbon cycle and has implications for future missions to detect possible past martian life.

The high D/H of the Martian atmosphere (∼5–6 × terrestrial) is considered strong evidence for the loss of Martian water to space. The timing and magnitude of the loss of water from Mars can be constrained by measurements of D/H in Martian meteorites. Previous studies of Martian meteorites have shown a large range in D/H, from terrestrial values to as high as the current Martian atmosphere. Here we show that the ancient (∼4 Ga) Mars meteorite ALH84001 has a D/H 4 × terrestrial and that the young (∼0.17 Ga) Shergotty meteorite has a D/H 5.6 × terrestrial. We also find that the young Los Angeles shergottite has zoning in D/H that can be correlated to igneous growth zoning, strongly suggesting assimilation of D‐enriched water during igneous crystallization near the Martian surface. In contrast to previous studies, we find higher and less variable D/H ratios in these three meteorites. Our results suggest a two‐stage evolution for Martian water—a significant early loss of water to space (prior to 3.9 Ga) followed by only modest loss to space in the last 4 billion years. The current Martian atmospheric D/H has remained essentially unchanged for the last 165 Ma.

Argon ion milling is the conventional means by which mineral sections are thinned to electron transparency for transmission electron microscope (TEM) analysis, but this technique exhibits significant shortcomings. In particular, selective thinning and imaging of submicrometer inclusions during sample milling are highly problematic. We have achieved successful results using the focused ion beam (FIB) lift-out technique, which utilizes a 30 kV Ga + ion beam to extract electron transparent specimens with nanometer scale precision. Using this procedure, we have prepared a number of Earth materials representing a range of structures and compositions for TEM analysis. We believe that FIB milling will create major new opportunities in the field of Earth and planetary materials microanalysis, particularly with respect to ultraprecious mineral and rock samples.

NASA's Stardust spacecraft collected dust particles from Comet 81P/Wild 2, at an encounter speed of ~6.1 km/s, into low-density, silica aerogel capture cells and in impact craters in the Al-

Nakhlites, clinopyroxenite meteorites from Mars, share common crystallization and ejection ages, suggesting that they might have been ejected from the same place on Mars by the same ejection event (impact) and are different samples of the same thick volcanic flow unit or shallow sill. Mean modal abundances and abundance ranges of pyroxene, olivine, and mesostasis vary widely among different thin-sections of an individual nakhlite. Lithologic heterogeneity is the main factor contributing to the observed modalabundance variations measured in thin-sections prepared from different fragments of the same stone. Two groups of nakhlites are distinguished from one another by which major constituent varies the least and the abundance of that constituent. The group consisting of Nakhla, Lafayette, Governador Valadares, and the Yamato nakhlite pairing group is characterized by low modal mesostasis and pyroxene-olivine covariance, whereas the group consisting of the Miller Range nakhlite pairing group and Northwest Africa 5790 is characterized by low modal olivine and pyroxene-mesostasis covariance. These two groups sample the slowest-cooled interior portion and the chilled margin, respectively, of the nakhlite emplacement body as presently understood, and appear to be also related to recently proposed nakhlite groups independently established using compositional rather than petrographic observations. Phenocryst modal abundances vary with inferred depth in the nakhlite igneous body in a manner consistent with solidification of the nakhlite stack from dynamically sorted phenocryst-rich magmatic crystal-liquid mush.

Zirconium alkylbisphosphonates are prepared by treating a derivatized substrate alternately with solutions of Zr4+ and a bisphosphonic acid. We report here the preparation of electroactive and photoactive metal phosphonate thin films, containing neutral and cationic organic groups. Electronic spectroscopy, ellipsometry, atomic force microscopy, and electron probe microanalysis were used to characterize the structure and composition of these thin films. An N,N‘-dialkylphenylenediamine bisphosphonate (1,4-bis(4-phosphonobutylamino)benzene) gives uniform lamellar thin films, with low root-mean-square roughness. The stoichiometry of this film is low in Zr relative to other zirconium bisphosphonate films [i.e., Zr0.75(bisphosphonate)]. Bisphosphonic acids with cationic organic groups (e.g., H2O3PCH2CH2−(4,4‘-bipyridinium)−CH2CH2PO3H2) do not follow the typical layered growth motif but instead form crystallites on the substrate surface. Lamellar growth in films prepared with neutral bisphosphonic acids can be perturbed by adding ammonium ions to the bisphosphonic acid growth solutions, leading to the growth of large crystallites. Electrochemical studies were carried out on crystallite films of viologen bisphosphonate based materials, grown on both gold foil and Sn[Sb]O x -coated glass substrates. The estimated reduction potential for viologen in these films (−0.83 V) is independent of film thickness but shows kinetic limitations that are directly related to film thickness. The E° of the viologen moiety in ZrPV(X) films is 150 mV more negative than that of dimethylviologen in solution or in other thin films.