Giant impacts during Earth’s final accretion likely generated global magma oceans, where the disproportionation of Fe ^2+ at lower mantle pressures and segregation of the resulting metallic iron into the core could have oxidized the magma ocean. Earth may nevertheless have had an H _2 -rich proto-atmosphere in chemical disequilibrium with the magma ocean, but the chemical coupling between this atmosphere and an oxidized magma ocean remains poorly constrained. Here, we develop a coupled interior-atmosphere evolution model that includes diffusive transport in the boundary layer between the magma ocean and atmosphere, redox reactions in the melt, partitioning of oxide components and H _2 O among coexisting phases, and planetary cooling through a proto-atmosphere, with metallic iron produced by Fe ^2+ disproportionation removed into the core as it forms. Atmospheric H _2 transport into the magma ocean and subsequent H _2 O production become more efficient with increasingly frequent boundary layer renewal driven by buoyant overturn of dense melt cooled at the surface, allowing the atmosphere and magma ocean to chemically equilibrate within ∼10 ^4 yr when the magma ocean is sufficiently deep and hot to extend into the lower mantle. Redox exchange with the atmosphere buffers the solidification-driven redox evolution of the magma ocean, preventing extreme oxidation or reduction of the coupled system. These results suggest that the coupled evolution could have contributed to early Earth’s water inventory while maintaining a reducing H _2 -rich atmosphere.
We analyze the dedicated postperihelion observations of interstellar comet 3I/ATLAS obtained by the Transiting Exoplanet Survey Satellite (TESS) during Sector 1751 on 2026 January 15–22. We search for coherent photometric modulation using both the public TESS Science Support Center aperture light curves and an independent, segment-centered aperture extraction from the released background-corrected image cubes. Candidate excursions are vetted at the pixel level, and periodic signals are evaluated using an exploratory 1–48 hr search, irregularly sampled Ornstein–Uhlenbeck simulations, segment-wise moving-block bootstraps, exact tests of eight previously reported periods, cross-product phase comparisons, and sinusoidal injection–recovery experiments. No candidate satisfies the predeclared family-wise, both-null, cross-product criterion. In particular, none of the reported approximately 7–8 or 15–17 hr period hypotheses is recovered as a statistically significant, phase-coherent modulation. The provider photometry reaches targeted 95% recovery thresholds of 19.0–25.0 ppt peak to peak at the literature periods, while the independent extraction reaches 29.5–38.6 ppt. No reviewed isolated excursion is securely attributable to the comet, and no statistically supported aperture-dilution signature is found. The TESS data therefore exclude a persistent coherent modulation comparable to the much larger amplitudes reported during parts of the preperihelion campaign, while remaining compatible with coma dilution, evolving activity morphology, nonstationary modulation, or non-principal-axis rotation.
Lunar Reconnaissance Orbiter Camera images have revealed thousands of young thrust fault scarps in the highlands and mare. These relatively small-scale faults are the expression of a period of late-stage lunar global contraction. Here we present the most comprehensive assessment of recent thrust faulting on the Moon and its implications for lunar radius change. Combining the estimate of the fractional areal strain of the highlands from the population of lobate thrust fault scarps with the fractional areal strain of the maria from the population of small mare ridge thrust faults, the total areal contractional strain is estimated to be ∼0.0048% to 0.0053%. This areal strain corresponds to a radial contraction of ∼42 to 46 m. Assuming a uniform rate of radius change over the last 400 Ma, the rate of change is estimated to be a maximum of ∼11 cm Ma ^−1 . The fractional areal strain of the maria contributes little to the total radius change, thus the late-stage radius change is dominated by the highland thrust faults. The isotropic compressional stress induced by this amount of radial contraction is estimated to be ∼4 MPa, consistent with stress drop estimates from recorded shallow moonquakes. Inconsistency between thermal history models that predict much larger amounts of radial contraction and the absence of degraded, ancient highland fault scarps supports a nonmonotonic lunar thermal evolution, possibly due to the insulating effects of a thick, porous megaregolith. Alternatively, the presence of a strong elastic lithosphere may have inhibited thrust faulting until stresses reached a threshold level in the Copernican era.
A widely used approach in planetary science to describe the strength and behavior of geological materials is the Mohr–Coulomb equation, yet it actually represents a linear approximation to a nonlinear failure envelope that breaks down at low confining stress. Using an established failure model, we show that while the majority of laboratory and terrestrial conditions lie in the linear regime, low-gravity planetary surfaces are situated in the nonlinear regime, where the bulk mechanical properties (apparent friction angle, apparent cohesion, and shear strength), become strongly stress dependent. We demonstrate that this nonlinearity governs the mechanical response of regolith in the limits of extremely low confining pressure found on low-gravity small-body surfaces, providing an explanation for the observations of very weak and uncohesive asteroid and cometary surfaces. Furthermore, we also show that mechanical properties of small-body regolith vary strongly with depth, with the apparent cohesion varying by orders of magnitude between the upper centimeters and depths of several meters. These results demonstrate that the widespread assumption of constant, stress-independent friction angle and bulk cohesion, inherent to linear strength models, fundamentally misrepresents regolith behaviour under low-gravity conditions, with important implications for small-body geomorphology, surface and rubble pile evolution, regolith simulants, and planetary exploration.
Salts on Ceres may act as messengers of interior ocean chemistry, trapping organics and preserving parent brine compositions. However, relating organic detections to subsurface brine compositions requires quantifying how much organic material is retained in salt crystals relative to the parent solution, a ratio, to our knowledge, not yet measured for any organic–salt system relevant to ocean worlds. Here, we determine the apparent partition coefficient, α , for glycine (NH _2 CH _2 COOH), the simplest and most abundant amino acid in extraterrestrial materials, crystallized in halite (NaCl) from aqueous brine under evaporative conditions. Halite crystals were grown from brines containing 0–133 mM glycine and characterized using optical microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray computed tomography (XCT), and gas chromatography with flame ionization detection (GC-FID). Reflected-light imaging and XCT reveal glycine incorporated as micrometer-scale inclusions rather than substituting into the crystal lattice, with crystal-to-crystal variability consistent with stochastic inclusion trapping. GC-FID yields a linear relationship between glycine concentration in the crystal and the parent brine, with α = 0.177 ± 0.019, meaning NaCl captured ∼18% of available glycine. Applied to Ceres, this implies that glycine concentrations in the subsurface reservoir can be at least 5 times higher than abundances in surface salt deposits and that individual salt grains may be heterogeneous even from a single source brine. This framework provides quantitative constraints for interpreting organic signatures observed in samples returned by a future Ceres mission, as recommended by the 2023–2032 Origins, Worlds, and Life Planetary Science and Astrobiology Decadal Survey.
