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Abstract:

Ultrashort-period (USP) exoplanets—with Rp ≤ 2R⊕ and periods ≤1 day—are expected to be stripped of volatile atmospheres by intense host star irradiation, which is corroborated by their nominal bulk densities and previous eclipse observations, consistent with bare-rock surfaces. However, a few USP planets appear anomalously underdense relative to an Earth-like composition, suggesting an exotic interior structure (e.g., coreless) or a volatile-rich secondary atmosphere increasing their apparent radius. Here, we present the first dayside emission spectrum of the low-density (4.3 ± 0.4 g cm−3) USP planet TOI-561 b, which orbits an iron-poor, alpha-rich, ∼10 Gyr old thick-disk star. Our 3–5 μm JWST/NIRSpec observations demonstrate the dayside of TOI-561 b is inconsistent with a bare-rock surface at high statistical significance, suggesting instead a thick volatile envelope that is cooling the dayside to well below the ∼3000 K expected in the bare-rock or thin-atmosphere case. These results reject the popular hypothesis of complete atmospheric desiccation for highly irradiated exoplanets and 91̽�� predictions that planetary-scale magma oceans can retain substantial reservoirs of volatiles, opening up the geophysical study of ultrahot super-Earths through the lenses of their atmospheres.

Abstract:

In Titan’s atmosphere, the chemistry of simple hydrocarbons (e.g., CH4 and C2H2) and nitrogen bearing species (e.g., N2 and CN) represents an important link between molecular species and the ubiquitous organic haze that gives Titan its characteristic orange hue. Here we present a new search for two previously undetected molecules, triacetylene (C6H2) and the gas phase dicyanoacetylene (C4N2), using the Echelon-Cross-Echelle Spectrograph instrument on board the Stratospheric Observatory for Infrared Astronomy aircraft. We do not detect these two molecules but determine upper limits for their mixing ratios and column abundances. We find the 3σ upper limits on the uniform volume mixing ratio (VMR) above 100 km for C6H2 to be 4.3 × 10−11, which is lower than the photochemical model predictions. This new upper limit suggests that the growth of linear molecules is inhibited. We also put a strict upper limit on the uniform VMR for gas phase C4N2 above 125 km to be 1.0 × 10−10. This upper limit is well below the saturation mixing ratio at this altitude for C4N2 and greatly limits the feasibility of C4N2 forming ice from condensation.

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 Regolith and Ice Drill for Exploration of New Terrains (TRIDENT) is a 1 m class drill developed for capturing regolith and ice during the Volatiles Investigating Polar Exploration Rover (VIPER) and the Polar Resources Ice Mining Experiment (PRIME-1) lander missions to the south pole of the Moon. The drill employs decoupled rotation and percussion mechanisms to allow for three modes: rotation, percussion, and rotation–percussion, depending on operational goals and the material strength. TRIDENT can be operated in such a way that it can characterize subsurface material and deliver cuttings to the surface for characterization by other instruments. TRIDENT includes a drill-bit-integrated temperature sensor and an auger-integrated heater with a colocated temperature sensor 35 cm above the bit for thermal conductivity measurement. The heater can also be used in cases of ice adherence (freezing in) and to enhance the sublimation of ice from the cuttings pile. TRIDENT collects and delivers subsurface regolith onto the surface using a “bite” sampling approach: cuttings are captured in the auger flutes, the auger is retracted after drilling a 10 cm bite, and then 10 cm worth of cuttings are deposited onto the surface, forming a cuttings cone. This regolith cone is then analyzed by instruments Mass Spectrometer Observing Lunar Operations (MSOLO) and NIRVSS on the VIPER and MSOLO on the PRIME-1 missions. The drilling activity creates a seismic signal that can be detected on any associated inertial measurement unit that is turned on during the activity, which enables seismic science. TRIDENT represents two decades of technology development for planetary applications and could be deployed on any future missions to other solar system bodies. TRIDENT on the PRIME-1 mission has been successfully deployed in horizontal orientation (this orientation was due to the lander being in an off nominal landing orientation). All actuators, sensors, and heaters worked as designed. Even though the drill did not penetrate regolith, it was covered in regolith that fell onto the drill during the landing operation. VIPER is scheduled to launch to the Moon at the end of 2027 on Blue Origin’s Mk1 lander.