We present a comprehensive overview of a volume-complete sample of white dwarfs located within 40 pc of the Sun, a significant proportion of which were detected in Gaia Data Release 3 (DR3). Our DR3 sample contains 1076 spectroscopically confirmed white dwarfs, with just five candidates within the volume remaining unconfirmed (> 99 per cent spectroscopic completeness). Additionally, 28 white dwarfs were not in our initial selection from Gaia DR3, most of which are in unresolved binaries. We use Gaia DR3 photometry and astrometry to determine a uniform set of white dwarf parameters, including mass, effective temperature, and cooling age. We assess the demographics of the 40 pc sample, specifically magnetic fields, binarity, space density, and mass distributions.

A solid solution of the mineral feiite (Fe3TiO5) was recently discovered in a shock-induced melt pocket of the Shergotty martian shergottite. It is particularly interesting for its potential as an indicator of pressure-temperature (P-T) and oxygen fugacity in martian crustal and mantle material. To date, complete crystallographic analysis of feiite has not been conducted, as the mineral was previously analyzed by electron backscatter diffraction on micrometer-size grains (Ma et al. 2021). Here we report a convergent crystal-structure model for feiite based on synchrotron single-crystal X-ray diffraction data collected on three grains of feiite synthesized at 12 GPa and 1200 degrees C. Feiite adopts the CaFe3O5 structure type (Cmcm, Z = 4), which is composed of two octahedral M1 and M2 sites and one trigonal prismatic M3 site (M = metal) in a ratio of 1:2:1. The three feiite grains with composition Ti0.46-0.60Fe3.54-3.40O5 were best modeled by substituting Ti4+ into only the octahedral M2 site, accounting for 30% of this site. Comparisons of the measured average bond lengths in the coordination polyhedra with the optimized Ti4+-O, Fe2+-O, and Fe3+-O bond lengths suggest that ferrous iron occupies the trigonal M3 site, while iron is mixed valence in the octahedral M1 and M2 sites. The Ti4+ and Fe3+ content constrained by our crystal-chemical analyses suggests that at least similar to 30% of the available iron must be ferric (i.e., Fe3+/Fe-total = 0.3) for the sample synthesized at 12 GPa and 1200 degrees C and higher P-T conditions may be needed to form the end-member feiite (Fe32+TiO5)

Molecular assembly indices, which measure the number of unique sequential steps theoretically required to construct a three-dimensional molecule from its constituent atomic bonds, have been proposed as potential biosignatures. A central hypothesis of assembly theory is that any molecule with an assembly index >= 15 found in significant local concentrations represents an unambiguous sign of life. We show that abiotic molecule-like heteropolyanions, which assemble in aqueous solution as precursors to some mineral crystals, range in molecular assembly indices from 2 for H2CO3 or Si(OH)4 groups to as large as 21 for the most complex known molecule-like subunits in the rare minerals ewingite and ilmajokite. Therefore, values of molecular assembly indices >= 15 do not represent unambiguous biosignatures.

Compression of small molecules can induce solid-state reactions that are difficult or impossible under conventional, solution-phase conditions. Of particular interest is the topochemical-like reaction of arenes to produce polymeric nanomaterials. However, high reaction onset pressures and poor selectivity remain significant challenges. Herein, the incorporation of electron-withdrawing and -donating groups into pi-stacked arenes is proposed as a strategy to reduce reaction barriers to cycloaddition and onset pressures. Nevertheless, competing side-chain reactions between functional groups represent alternative viable pathways. For the case of a diaminobenzene:tetracyanobenzene cocrystal, amidine formation between amine and cyano groups occurs prior to cycloaddition with an onset pressure near 9 GPa, as determined using vibrational spectroscopy, X-ray diffraction, and first-principles calculations. This work demonstrates that reduced-barrier cycloaddition reactions are theoretically possible via strategic functionalization; however, the incorporation of pendant groups may enable alternative reaction pathways. Controlled reactions between pendant groups represent an additional strategy for producing unique polymeric nanomaterials.

The Dominion Range (DOM) and Miller Range (MIL) dense collection areas (DCAs) have yielded more than 20 and 200 CO3 chondrites (carbonaceous chondrites of the Ornans chemical group), respectively, over multiple field seasons. Several samples have exhibited primitive characteristics and have been the focus of interest. With so many CO3s recovered from this area, a natural question is if there are multiple pairing groups (where pairing refers to two or more meteorites that are part of a single fall) and if there is additional primitive material that would interest the meteorite community. This comprehensive study looks at all samples using several approaches: field and macroscopic observations; magnetic susceptibility; Cr in ferroan olivine; bulk elemental and isotopic analysis of H, C, N, and noble gas analyses to determine cosmic ray exposure (CRE) ages. Magnetic susceptibilities (measured as log chi) for all samples correlate with their type II (i.e., FeO-rich) olivine Cr contents, with the most primitive CO3s (3.00) have log chi values near 5, while the higher grade CO3s have log chi values as low as 4.17. Altogether, there appear to be two distinct CO3 pairing groups and five other unpaired CO3s recovered at the Dominion Range: (a) the main DOM 08004 pairing group (16 specimens with a CRE age of 10-16 Ma), (b) the DOM 08006 group (2 specimens incl. DOM 10847 with a CRE age of 25 Ma), (c) DOM 14359 with a CRE age of 6 Ma, (d) DOM 18070 with a CRE age of 8 Ma (these two samples have similar ages but distinct trapped Ne-20 contents), (e) DOM 10900 with a CRE age of 5.5 Ma, (f) DOM 18286 (with a CRE age of similar to 59 Ma), and (g) DOM 19034 (with a CRE age of similar to 43 Ma). There are three distinct age groupings of 3.00-3.05 COs, highlighting the diverse pristine CO3 materials present in the DOM area. There is one large MIL pairing group (MIL 07099; n = 199; 9-14 Ma CRE age where measured) and one smaller pairing group with distinctly lower Cr2O3 in type II olivines (8 samples of unknown CRE age), and five unpaired or unique CO3s. Notably, the large DOM and MIL pairing groups have 9-16 Ma exposure ages that could have been delivered in a single large fall event spanning similar to 200 km, two separate falls that were ejection paired, or two separate falls from two separate ejections. Finally, we recommend reclassifying several CO3 to CM2 based on new data and that from previous studies.

The recent discovery of "ultrahot" (P < 1 day) Neptunes has come as a surprise: some of these planets have managed to retain gaseous envelopes despite being close enough to their host stars to trigger strong photoevaporation and/or Roche lobe overflow. Here, we investigate atmospheric escape in LTT 9779b, an ultrahot Neptune with a volatile-rich envelope. We observed two transits of this planet using the newly commissioned WINERED spectrograph (R similar to 68,000) on the 6.5 m Clay/Magellan II Telescope, aiming to detect an extended upper atmosphere in the He 10830 angstrom triplet. We found no detectable planetary absorption: in a 0.75 angstrom passband centered on the triplet, we set a 2 sigma upper limit of 0.12% (delta R-p/H < 14) and a 3 sigma upper limit of 0.20% (delta R-p/H < 22). Using a H/He isothermal Parker wind model, we found corresponding 95% and 99.7% upper limits on the planetary mass-loss rate of M<10(10.03) g s(-1) and M<10(11.11) g s(-1), respectively, smaller than predicted by outflow models even considering the weak stellar X-ray and ultraviolet emission. The low evaporation rate is plausibly explained by a metal-rich envelope, which would decrease the atmospheric scale height and increase the cooling rate of the outflow. This hypothesis is imminently testable: if metals commonly weaken planetary outflows, then we expect that JWST will find high atmospheric metallicities for small planets that have evaded detection in He 10830 angstrom.

In photosynthetic organisms light acts as an environmental signal to control their development and physiology, and as energy source to drive the conversion of CO2 into carbohydrates used for growth or storage. The main storage carbohydrate in green algae is starch, which accumulates during the day and is broken down at night to meet cellular energy demands. The signalling role of light quality in the regulation of starch accumulation remains unexplored. Here, we report that in the model green alga Chlamydomonas reinhardtii blue light perceived by the photoreceptor PHOTOTROPIN causes dephosphorylation of the PHOTOTROPIN-MEDIATED SIGNALLING KINASE 1 that then suppresses starch accumulation by inhibiting the expression of GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE. Our results provide an in-depth view of how photoreceptor-mediated signalling controls microalgal carbon metabolism.

The search for rocky planet atmospheres with JWST has focused on planets transiting M dwarfs. Such planets have favorable planet-to-star size ratios, enhancing the amplitude of atmospheric features. Since the expected signal strength of atmospheric features is similar to the single-transit performance of JWST, multiple observations are required to confirm any detection. Here, we present two transit observations of the rocky planet GJ 1132 b with JWST NIRSpec G395H, covering 2.8-5.2 mu m. Previous Hubble Space Telescope WFC3 observations of GJ 1132 b were inconclusive, with evidence reported for either an atmosphere or a featureless spectrum based on analyses of the same data set. Our JWST data exhibit substantial differences between the two visits. One transit is consistent with either an H2O-dominated atmosphere containing similar to 1% CH4 and trace N2O ( chi nu 2=1.13 ) or stellar contamination from unocculted starspots ( chi nu 2=1.36 ). However, the second transit is consistent with a featureless spectrum. Neither visit is consistent with a previous report of HCN. Atmospheric variability is unlikely to explain the scale of the observed differences between the visits. Similarly, our out-of-transit stellar spectra show no evidence of changing stellar inhomogeneity between the two visits-observed 8 days apart, only 6.5% of the stellar rotation rate. We further find no evidence of differing instrumental systematic effects between visits. The most plausible explanation is an unlucky random noise draw leading to two significantly discrepant transmission spectra. Our results highlight the importance of multivisit repeatability with JWST prior to claiming atmospheric detections for these small, enigmatic planets.