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The stellar occultation technique is capable of atmospheric trace gas detection using the molecule absorption characteristics of the stellar spectra. In this paper, the non-iterative and iterative retrieval methods for oxygen and air density detection by stellar occultation are investigated. For the single-band average transmission data in the oxygen 761 nm A-band, an onion-peeling algorithm is used to calculate the effective optical depth of each atmospheric layer, and then the optical depth is used to retrieve the oxygen number density. The iteration method introduces atmospheric hydrostatic equilibrium and the ideal gas equation of state, and it achieves a more accurate retrieval of the air density under the condition of a priori temperature deviation. Finally, this paper analyzes the double solution problem in the iteration process and the ideas to improve the problem. This paper provides a theoretical basis for the development of a new type of atmospheric density detection method. [ABSTRACT FROM AUTHOR]

We use the extensive stellar occultation data set of the Imaging Ultraviolet Spectrograph aboard the Mars Atmosphere and Volatile EvolutioN spacecraft to determine the first quantification of vertical variation in O2 mole fraction separately for day and night in the ∼90–130 km altitude range. The upper atmospheric O2 variation is expected to be due to the interplay between diffusion and advection because of its long photochemical lifetime. It is therefore a useful tracer of the state of atmospheric mixing and circulation. The altitude‐averaged mixing ratio is measured to be 2.69(±0.03) × 10−3 for the nightside and 2.05(±0.03) × 10−3 for the dayside. The average O2 mole fraction for day and night are nearly identical below 105 km, consistent with the value of 1.61 × 10−3 derived from the Mars Curiosity Rover/Sample Analysis at Mars near‐surface measurements. At higher altitudes, dominated by molecular diffusive separation, the measured O2 mole fraction demonstrates a vertical gradient with a local time dependence. The nightside mole fraction is a factor of 1.37 ± 0.04 larger than the dayside value at ∼125 km. This nightside enhancement is explained in terms of the relative role of solar‐driven rapid horizontal winds at high altitudes and slower vertical diffusion, resulting in a nightside (dayside) downward (upward) diffusive flux. Using the 1‐D diffusion model, the measured profiles correspond to a vertical eddy diffusion coefficient K = 3.5(±1.5) × 106 cm2/s. The Mars Climate Database predicts comparable but lower day‐night differences in oxygen mole fraction due to an overestimated K = 7.0(±1.0) × 106 cm2/s, which affects atmospheric mixing as well as the rate of atmospheric escape to space. Plain Language Summary: Molecular oxygen in the martian atmosphere is produced photochemically and behaves like an inert trace gas due to its long photochemical lifetime (∼60 Earth years). Its variations in the upper atmosphere are therefore governed by diffusion and dynamics and are indicative of the changes in atmospheric mixing and circulation. Other data sets have only provided a glimpse of O2 abundance in the upper atmosphere due to limited spatial and temporal coverage. The extensive stellar occultation data set of the Imaging Ultraviolet Spectrograph aboard the Mars Atmosphere and Volatile EvolutioN spacecraft can help fill this knowledge gap. This study shows the first quantification of vertical variation in O2 mixing ratio separately for day and night in the ∼90–130 km altitude range. While the day and night O2 mixing ratio is measured to be identical below 105 km in the well‐mixed atmosphere, significant local time dependence is seen under molecular diffusive separation, with a nightside enhancement and a dayside depletion. This is explained in terms of diffusive flux from the dayside to the nightside. However, the Mars Climate Database output is inconsistent with these measurements, which therefore have important implications for how species diffuse through the martian atmosphere and escape to space. Key Points: Stellar occultations observed by Mars Atmosphere and Volatile EvolutioN/Imaging Ultraviolet Spectrograph allow the most complete study of molecular oxygen in the upper atmosphereSignificant day/night differences reveal the importance of diurnal circulation and molecular diffusionObserved day/night differences exceed those in models, suggesting mixing is significantly overestimated in those models [ABSTRACT FROM AUTHOR]

The stellar occultation technique is capable of atmospheric trace gas detection using the molecule absorption characteristics of the stellar spectra. In this paper, the non-iterative and iterative retrieval methods for oxygen and air density detection by stellar occultation are investigated. For the single-band average transmission data in the oxygen 761 nm A-band, an onion-peeling algorithm is used to calculate the effective optical depth of each atmospheric layer, and then the optical depth is used to retrieve the oxygen number density. The iteration method introduces atmospheric hydrostatic equilibrium and the ideal gas equation of state, and it achieves a more accurate retrieval of the air density under the condition of a priori temperature deviation. Finally, this paper analyzes the double solution problem in the iteration process and the ideas to improve the problem. This paper provides a theoretical basis for the development of a new type of atmospheric density detection method.

Gaussian process (GP) regression is a nonparametric Bayesian approach that has been used successfully in various astronomical domains, especially in time-domain astronomy. The most common applications are the smoothing of data for interpolation and the detection of periodicities. The ability to create unbiased data-driven models without a predefined physical model can be a major advantage over conventional regression methods. Prior knowledge can be included by setting boundary conditions or constraining hyperparameter values, while unknown hyperparameters are optimized during the conditioning of the model. We have adapted and transformed previous approaches of GP regression and introduce three new applications for this regression method, especially in the context of stellar occultations: the modeling of occultation light curves, the correction of public JPL ephemerides of minor planets based on publicly available image data of the Zwicky Transient Facility, and the detection of natural satellites. We used data from observations of stellar occultations to validate the models and achieved promising results in all cases, and thus we confirmed the flexibility of GP regression models. Considering various existing use cases in addition to our novel applications, GP regression can be used to model diverse data sets addressing a wide range of problems. The accuracy of the model depends on the input data and on the set boundary conditions. Generally, high-quality data allow the usage of loose boundary conditions, while low-quality data require more restrictive boundary conditions to avoid overfitting.

Ultraviolet spectroscopy is a powerful method to study planetary surface composition through reflectance measurements, atmospheric composition through stellar/solar occultations, transits of other planetary bodies, and direct imaging of airglow and auroral emissions. The next generation of ultraviolet spectrographs (UVS) on board ESA’s Jupiter Icy Moons Explorer and NASA’s Europa Clipper missions will perform such measurements of Jupiter and its moons in the early 2030s. This work presents a compilation of a detailed UV stellar catalog, named Catalog of Ultraviolet Bright Stars (CUBS), of targets with high intensity in the 50–210 nm wavelength range with applications relevant to planetary spectroscopy. These applications include (1) planning and simulating occultations, including calibration measurements; (2) modeling starlight illumination of dark, nightside planetary surfaces primarily lit by the sky; and (3) studying the origin of diffuse Galactic UV light as mapped by existing data sets from Juno-UVS and others. CUBS includes observations from the International Ultraviolet Explorer (IUE) and additional information from the SIMBAD database. We have constructed model spectra at 0.1 nm resolution for almost 90,000 targets using interpolated Kurucz models (which have a resolution of 1 nm) and, when available, IUE spectra. CUBS also includes robust checks for agreement between the Kurucz models and the IUE data. We also present a tool for which our catalog can be used to identify the best candidates for stellar occultation observations, with applications for any UV instrument. We report on our methods for producing CUBS and discuss plans for its implementation during ongoing and upcoming planetary missions.

The satellite Mimas launches a bending wave – a warping of the rings that propagates radially through self-gravity – at the 5:3 inner vertical resonance with Saturn's rings. We present a modification of the linear bending wave theory (Shu et al., 1983) which includes the effects of satellite self-gravity wakes on the particles in the wave. We show that, when treated as rigid, these wakes generate an extra layer of particles whose number density is proportional to the magnitude of the slope of the warped ring. Using a ray-tracing code we compare our predictions with those of Shu et al. (1983) and with 60 stellar occultations observed by the Cassini Ultraviolet Imaging Spectrograph (UVIS) and find that the extra layer of particles of our perturbed bending wave model has a considerable explanatory power for the UVIS dataset. Our best model explains the most discrepant and surprising features of the Mimas 5:3 bending wave; the enhancement of the signal for the cases of occultations with high ring opening angle and the bigger-than-expected viscosity, ν = 576 cm2/s, which is more than double the viscosity computed from density waves (Tiscareno et al., 2007). This shows that self-gravity wakes can be effective at transporting angular momentum in a vertically perturbed disk. Relative to neighboring density waves (Tiscareno et al., 2007), we find a lower-than-expected value for the surface mass density, σ = 36.7 g/cm2, which suggests that the enhanced viscous interactions may be transporting material into the surrounding regions. • Modified wave theory matches the Cassini data significantly better than previous attempts. • Extra layer of particles explains most discrepant aspects between previous theory and data. • Bending waves enhances local viscosity up to a factor of 5, this can have secular dynamical effects. • The local viscosity enhancement occurs due to the self-gravity wake-bending wave interaction. • The obtained surface mass density is smaller than others in the region, suggesting mass transport. [ABSTRACT FROM AUTHOR]