The search for definitive biosignatures-unambiguous markers of past or present life-is a central goal of paleobiology and astrobiology. We used pyrolysis-gas chromatography coupled to mass spectrometry to analyze chemically disparate samples, including living cells, geologically processed fossil organic material, carbon-rich meteorites, and laboratory-synthesized organic compounds and mixtures. Data from each sample were employed as training and test subsets for machine-learning methods, which resulted in a model that can identify the biogenicity of both contemporary and ancient geologically processed samples with similar to 90% accuracy. These machine-learning methods do not rely on precise compound identification: Rather, the relational aspects of chromatographic and mass peaks provide the needed information, which underscores this method's utility for detecting alien biology.

For the first time on Mars, the crystalline magnesium-sulfate mineral starkeyite (MgSO4 center dot 4H(2)O) was definitively identified using the CheMin X-ray diffraction instrument at Gale crater. At the Canaima drill site, starkeyite along with amorphous MgSO4 center dot nH(2)O are among the "polyhydrated Mg-sulfates" interpreted in orbital reflectance spectra. Mg-sulfates are good climate indicators as they are very responsive to changes in temperature and relative humidity. We hypothesize that, through evaporation, Mg-sulfates formed at the end of brine evolution when ion concentrations became saturated and precipitated on the surface or near sub-surface as either epsomite or meridianiite. These minerals were subsequently dehydrated later to starkeyite and amorphous MgSO4 center dot nH(2)O in response to a drier Mars. At Canaima, starkeyite is stable and would form during the warmer Mars summers. Due to very slow kinetics at the low Mars winter temperatures, starkeyite and amorphous MgSO4 center dot nH(2)O would be resistant to recrystallize to more hydrous forms and thus likely persist year-round. During the course of analyses, starkeyite transforms into amorphous MgSO4 center dot nH(2)O inside the rover body due to the elevated temperature and greatly reduced relative humidity compared to the martian surface at the Canaima drill site. It is possible that crystalline sulfate minerals existed in earlier samples measured by CheMin but altered inside the rover before they could be analyzed. Starkeyite is most likely prevalent in the subsurface, whereas both starkeyite and amorphous MgSO4 center dot nH(2)O are likely present on the surface as starkeyite could partially transform into amorphous MgSO4 center dot nH(2)O due to direct solar heating.

The origin of Earth's volatile elements is highly debated. Comparing the chalcogen isotope ratios in the bulk silicate Earth (BSE) to those of its possible building blocks, chondritic meteorites, allows constraints on the origin of Earth's volatiles; however, these comparisons are complicated by potential isotopic fractionation during protoplanetary differentiation, which largely remains poorly understood. Using first-principles calculations, we find that core-mantle differentiation does not notably fractionate selenium and tellurium isotopes, while equilibrium evaporation from early planetesimals would enrich selenium and tellurium in heavy isotopes in the BSE. The sulfur, selenium, and tellurium isotopic signatures of the BSE reveal that protoplanetary differentiation plays a key role in establishing most of Earth's volatile elements, and a late veneer does not substantially contribute to the BSE's volatile inventory.

We present a detailed chemical abundance analysis of the brightest star in the ultrafaint dwarf (UFD) galaxy candidate Cetus II from high-resolution Magellan/MIKE spectra. For this star, DES J011740.53-173053, abundances or upper limits of 18 elements from carbon to europium are derived. Its chemical abundances generally follow those of other UFD galaxy stars, with a slight enhancement of the alpha-elements (Mg, Si, and Ca) and low neutron-capture element (Sr, Ba, and Eu) abundances supporting the classification of Cetus II as a likely UFD. The star exhibits lower Sc, Ti, and V abundances than Milky Way (MW) halo stars with similar metallicity. This signature is consistent with yields from a supernova originating from a star with a mass of similar to 11.2 M-circle dot. In addition, the star has a potassium abundance of [K/Fe] = 0.81, which is somewhat higher than the K abundances of MW halo stars with similar metallicity, a signature that is also present in a number of UFD galaxies. A comparison including globular clusters and stellar stream stars suggests that high K is a specific characteristic of some UFD galaxy stars and can thus be used to help classify objects as UFD galaxies.

It has been suggested that beta Pic b has a supersolar metallicity and subsolar C/O ratio. Assuming solar carbon and oxygen abundances for the star beta Pic and therefore the planet's parent protoplanetary disk, beta Pic b's C/O ratio suggests that it formed via core accretion between its parent protoplanetary disk's H2O and CO2 ice lines. However, beta Pic b's high metallicity is difficult to reconcile with its mass M-p = 11.7 M-Jup. Massive stars can present peculiar photospheric abundances that are unlikely to record the abundances of their former protoplanetary disks. This issue can be overcome for early-type stars in moving groups by inferring the elemental abundances of the FGK stars in the same moving group that formed in the same molecular cloud and presumably share the same composition. We infer the photospheric abundances of the F dwarf HD 181327, a beta Pic moving group member that is the best available proxy for the composition of beta Pic b's parent protoplanetary disk. In parallel, we infer updated atmospheric abundances for beta Pic b. As expected for a planet of its mass formed via core-accretion beyond its parent protoplanetary disk's H2O ice line, we find that beta Pic b's atmosphere is consistent with stellar metallicity and confirm that it has superstellar carbon and oxygen abundances with a substellar C/O ratio. We propose that the elemental abundances of FGK dwarfs in moving groups can be used as proxies for the otherwise difficult-to-infer elemental abundances of early-type and late-type members of the same moving groups.

We present the stellar mass-stellar metallicity relation for 3491 star-forming galaxies at 2 less than or similar to z less than or similar to 3 using rest-frame far-ultraviolet spectra from the Ly alpha Tomography IMACS Survey (LATIS). We fit stellar population synthesis models from the Binary Population And Spectral Synthesis code (v2.2.1) to medium-resolution (R similar to 1000) and high signal-to-noise (>30 per 100 km s(-1) over the wavelength range 1221-1800 & Aring;) composite spectra of galaxies in bins of stellar mass to determine their stellar metallicity, primarily tracing Fe/H. We find a strong correlation between stellar mass and stellar metallicity, with stellar metallicity monotonically increasing with stellar mass at low masses and flattening at high masses (M-* greater than or similar to 10(10.3)M(circle dot)). Additionally, we compare our stellar metallicity measurements with the gas-phase oxygen abundance of galaxies at similar redshift and estimate the average [alpha/Fe] similar to 0.6. Such high alpha-enhancement indicates that high-redshift galaxies have not yet undergone significant iron enrichment through Type Ia supernovae. Moreover, we utilize an analytic chemical evolution model to constrain the mass loading parameter of galactic winds as a function of stellar mass. We find that as the stellar mass increases, the mass loading parameter decreases. The parameter then flattens or reaches a turning point at around M-* similar to 10(10.5)M(circle dot). Our findings may signal the onset of black-hole-driven outflows at z similar to 2.5 for galaxies with M-* greater than or similar to 10(10.5) M-circle dot.

Dwarf galaxies are found to have lost most of their metals via feedback processes; however, there still lacks consistent assessment on the retention rate of metals in their circumgalactic medium (CGM). Here we investigate the metal content in the CGM of 45 isolated dwarf galaxies with M * = 106.5-9.5 M circle dot (M 200m = 1010.0-11.5 M circle dot) using the Hubble Space Telescope/Cosmic Origins Spectrograph. While H i (Ly alpha) is ubiquitously detected (89%) within the CGM, we find low detection rates (approximate to 5%-22%) in C ii, C iv, Si ii, Si iii, and Si iv, largely consistent with literature values. Assuming these ions form in the cool (T approximate to 104 K) CGM with photoionization equilibrium, the observed H i and metal column density profiles can be best explained by an empirical model with low gas density and high volume filling factor. For a typical galaxy with M 200m = 1010.9 M circle dot (median of the sample), our model predicts a cool gas mass of M CGM,cool similar to 108.4 M circle dot, corresponding to similar to 2% of the galaxy's baryonic budget. Assuming a metallicity of 0.3 Z circle dot, we estimate that the dwarf galaxy's cool CGM likely harbors similar to 10% of the metals ever produced, with the rest either in more ionized states in the CGM or transported to the intergalactic medium. We further examine the EAGLE simulation and show that H i and low ions may arise from a dense cool medium, while C iv arises from a diffuse warmer medium. Our work provides the community with a uniform data set on dwarf galaxies' CGM that combines our recent observations, additional archival data and literature compilation, which can be used to test various theoretical models of dwarf galaxies.

We report Nd and Sm isotopic compositions of four samples of Ryugu returned by the Hayabusa2 mission, including "A" (first touchdown) and "C" (second touchdown) samples, and several carbonaceous chondrites to evaluate potential genetic relationships between Ryugu and known chondrite groups and track the cosmic ray exposure history of Ryugu. We resolved Nd and Sm isotopic anomalies in small (<20 ng Nd and Sm) sample sizes via thermal ionization mass spectrometer using 10(13) Omega amplifiers. Ryugu samples exhibit resolvable negative mu Nd-142 values consistent with carbonaceous chondrite values, suggesting that Ryugu is related to the parent bodies of carbonaceous chondrites. Ryugu's negative mu Sm-149 values are the result of exposure to galactic cosmic rays, as demonstrated by the correlation between Sm-150/Sm-152 and Sm-149/Sm-152 ratios that fall along the expected neutron capture correlation line. The neutron fluence calculated in the "A" samples (2.75 +/- 1.94 x 10(15) n cm(-2)) is slightly higher compared to the "C" samples (0.95 +/- 2.04 x 10(15) n cm(-2)), though overlapping within measurement uncertainty. The Sm results for Ryugu, at this level of precision, thus are consistent with a well-mixed surface layer at least to the depths from which the "A" and "C" samples derive.

Protein O-glycosylation is a nutrient signaling mechanism that plays an essential role in maintaining cellular homeostasis across different species. In plants, SPINDLY (SPY) and SECRET AGENT (SEC) posttranslationally modify hundreds of intracellular proteins with O-fucose and O-linked N-acetylglucosamine, respectively. SPY and SEC play overlapping roles in cellular regulation, and loss of both SPY and SEC causes embryo lethality in Arabidopsis (Arabidopsis thaliana). Using structure-based virtual screening of chemical libraries followed by in vitro and in planta assays, we identified a SPY O-fucosyltransferase inhibitor (SOFTI). Computational analyses predicted that SOFTI binds to the GDP-fucose-binding pocket of SPY and competitively inhibits GDP-fucose binding. In vitro assays confirmed that SOFTI interacts with SPY and inhibits its O-fucosyltransferase activity. Docking analysis identified additional SOFTI analogs that showed stronger inhibitory activities. SOFTI treatment of Arabidopsis seedlings decreased protein O-fucosylation and elicited phenotypes similar to the spy mutants, including early seed germination, increased root hair density, and defective sugar-dependent growth. In contrast, SOFTI did not visibly affect the spy mutant. Similarly, SOFTI inhibited the sugar-dependent growth of tomato (Solanum lycopersicum) seedlings. These results demonstrate that SOFTI is a specific SPY O-fucosyltransferase inhibitor that can be used as a chemical tool for functional studies of O-fucosylation and potentially for agricultural management.