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Abstract:

Some oxidized compounds in Martian soils may form through heterogeneous electrochemistry (HEC) stimulated by electrostatic discharge (ESD) during dust storms and dust devils. To test this hypothesis, we conducted medium-strength ESD experiments in a Mars simulation chamber and analyzed the Cl, O, and C isotopic compositions of the resulting chloride, (per)chlorate, and carbonate products. These ESD products exhibit substantial mass-dependent depletions in heavy isotopes: ε 37Cl from -11.3 ‰ to +2.0 ‰, ε 18O from -34.5 ‰ to -12.9 ‰, and ε 13C around -11.4 ‰. These results, when compared with isotopic measurements from recent Mars missions (ESA’s ExoMars Trace Gas Orbiter and the Sample Analysis at Mars (SAM) instrument package aboard NASA’s Curiosity rover) and Martian meteorites, indicate that HEC induced by Martian dust activities can account for a substantial portion of the (per)chlorates and carbonates identified at the surface of Mars.

Abstract:

Atmospheric convection behaves differently in hydrogen-rich atmospheres compared to higher mean molecular weight atmospheres due to compositional gradients of tracers. Previous 1D studies predict that when a condensable tracer exceeds a critical mixing ratio in H2-rich atmospheres, convection is inhibited, leading to the formation of radiative layers where the temperature decreases faster with height than in convective profiles. We use 3D convection-resolving simulations to test whether convection is inhibited in H2-rich atmospheres when the tracer mixing ratio exceeds the critical threshold, while including processes neglected in 1D, e.g., turbulent mixing and evaporation. We run two sets of simulations. First, we perform simulations initialized on saturated isothermal states and find that compositional gradients can destabilize isothermal atmospheres. Second, we perform simulations initialized on adiabatic profiles, which show distinct, stable inhibition layers form when the condensable tracer exceeds the critical threshold. Within the inhibition layer, only a small amount of energy is carried by latent heat flux, and turbulent mixing transports a small amount of tracer upward, but both are generally too weak to sustain substantial tracer or heat transport. The thermal profile gradually relaxes to a steep radiative state, but radiative relaxation timescales are long. Our results suggest stable layers driven by condensation-induced convective inhibition form in H2-rich atmospheres, including those of sub-Neptune exoplanets.

Abstract:

Astrobotic's Peregrine Mission-1 spacecraft experienced a propulsion system anomaly that prevented the lander from reaching the Moon. During the mission, several instruments operated successfully in cis-lunar space. Among them, the Peregrine Ion Trap Mass Spectrometer (PITMS) measured both the presence of outgassing water and nitrogen oxides traceable to the MON-25 oxidizer. We performed Direct Simulation Monte Carlo (DSMC) studies of the oxidizer leak on Peregrine to characterize the gas diffusion from the leak to the instrument, mediated by inter-species collisions and gas–surface interaction. We conclude that the latter process was prevalent and that diffusion paths through Peregrine are necessary to explain the PITMS detections. Our DSMC study and estimation of Peregrine's outgassing rate suggest that, at the early stage of the mission, the spacecraft released water at a rate comparable to the Space Shuttle and at a much larger rate than typical spacecraft during science operations. This provides useful information for planning future operations of science instruments on commercial missions.

Abstract:

The Lucy spacecraft flew past the ∼738 m diameter, S-class main-belt asteroid (152830) Dinkinesh on 2023 November 1, revealing a satellite named Selam. We used images acquired during the flyby to evaluate surface features on both Dinkinesh and Selam. We find a shallow crater size–frequency distribution (SFD) for Dinkinesh, consistent with crater SFDs observed on other subkilometer asteroids. We derive crater depth-to-diameter ratios near 0.1, also consistent with typical values seen on other asteroids. We calculate a cumulative boulder SFD for Dinkinesh with power-law index 3.93 ± 0.15 slightly steeper though in the range of other S-class asteroids. We find growing evidence that boulder SFDs are, on average, steeper for S-class than C-complex asteroids. Two major surface features on Dinkinesh, Sumak Fossa (a large trough) and Fab Dorsum (an equatorial ridge), are likely an outcome of YORP spinning up Dinkinesh fast enough to produce failure. A self-consistent structure for Dinkinesh that complies with the global shape, feature morphologies, and the estimated 10–20 Myr YORP spin-up timescale is a rubble-pile object with a nearly strengthless surface and an interior strength that is less than tens of Pa. Selam could have formed via YORP-driven mass shedding from Dinkinesh, though other formation mechanisms are possible. Combining a low-strength surface with the crater population and an impact model, we estimate a ∼1 Myr surface age for Dinkinesh. The presence of mass wasting and young troughs indicates that stress accumulation and release continue on Dinkinesh to the present day.

Abstract:

Context. Characterizations of giant exoplanets such as β Pictoris b (hereafter β Pic b) are now routinely performed with multiple spectrographs and imagers exploring different spectral bandwidths and resolutions, allowing for atmospheric retrieval of spectra with or without the conservation of the planet spectral continuum. The accounting of data multimodality in the analysis could provide a more comprehensive determination of the planets physical and chemical properties and inform on their formation history. Aims. We present the first VLTI observations at R λ ∼4000 of β Pic b obtained for an exoplanet with GRAVITY at such a high resolution. We upgraded the forward modelling code ForMoSA to account for the data multimodality, including low-, medium-, and high-resolution spectroscopy based on both a direct model-data comparison and an analysis of cross-correlation signals. We used the ForMoSA code to refine the constraints on the atmospheric properties of the exoplanet and evaluated the sensitivity of the retrieved values to the input dataset. Methods. We obtained four high-signal-to-noise (S/N ∼ 20) spectra of β Pic b in the K band with GRAVITY at R λ ∼4000 conserving both the pseudo-continuum and the pattern of molecular absorptions. We used ForMoSA with four grids of self-consistent forward models (Exo-REM, ATMO, BT-Settl, and Sonora) to explore different T e ff , log(g), metallicity, C/O, and 12 CO/ 13 CO ratio values. We then combined the GRAVITY spectra with published 1–5 µm photometry (NaCo, VisAO, NICI, and SPHERE), low-to-mediumresolution ( R λ ≤ 700 broadband, 0.9–7 µm) spectra, and echelle spectra covering narrower bandwidths ( R λ ∼ 100 000, 2.1–5.2 µm). Results. Sonora and Exo-REM are statistically preferred among all four models, regardless of the dataset used. Exo-REM predicts T eff  = 1607.45 −6.20 +4.85 K and log(g) = 4.46 −0.04 +0.02 dex when using only the GRAVITY epochs, whereas we have T eff  = 1502.74 −2.14 +2.32 K log(g) = 4.00 ± 0.01 dex when incorporating all available datasets. The inclusion of archival data significantly affects all retrieved posteriors. When using all datasets, C/O mostly remains solar (0.552 −0.002 +0.003 ), while [M/H] reaches super-solar values (0.50 ± 0.01). We report the first tentative constraint on the isotopic ratio log( 12 CO/ 13 CO) = 1.12 −0.08 +0.11 in β Pic b’s atmosphere; however, we note that this detection remains inconclusive due to telluric residuals affecting both the GRAVITY and SINFONI data. Additionally, we estimated the bolometric luminosity as log(L/L ⊙ ) = −4.01 −0.05 +0.04 dex. Using a system age of 23 ± 3 Myr, along with this bolometric luminosity and the constraints on the dynamical mass of β Pic b, we were able to constrain the maximum of heavy element content of the planet to be on the order of 5% (20–80 M Earth ). Conclusions. The joint access to the pseudo-continuum and molecular lines in the K band provided by GRAVITY have a significant impact on the retrieved metallicity, possibly owing to the collision-induced absorption driving the continuum shape of the K band. The echelle spectra do not dominate the final fit with respect to lower resolution data covering a broader portion of the spectral energy distribution and the latter keeps encapsulating more robust information on T eff . Future multimodal frameworks should include a weighting scheme to account for the bandwidth and central wavelength of the observations.