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Ultraviolet spectral imaging has been a powerful tool to investigate the cloud top of Venus, allowing for measurement of several minor gases (especially SO 2 , SO, O 3), of cloud top aerosol's microphysical properties and of atmospheric dynamics through tracking of the unevenly distributed UV absorber. After a brief review of recent UV instruments that orbited around Venus, we present the results of a state-of-the-art radiative transfer model from Marcq et al. (2020) to derive the spectral resolution and Signal-to-Noise ratio (SNR) required to derive abundances of these gases, retrieve optical properties of the aerosols beyond our current knowledge. This leads us to propose a two-channel UV hyperspectral push-broom imager called VeSUV (standing for Venusian Spectroscopy in UV) whose technical characteristics will improve on existing measurements by a factor of at least 2, and which is well suited to the integration into the payload of future low Venus orbit platforms such as the proposed EnVision mission to ESA M5 call. [ABSTRACT FROM AUTHOR]

The deuterium to hydrogen (D/H) ratio is commonly used to investigate the history of water on Mars, yet the mechanisms controlling present‐day HDO behavior are poorly understood. Significant variations of the D/H ratio were first predicted on the basis of a 3D global climate model, which were later confirmed by ground‐based observations. This behavior, consisting of lower HDO/H2O ratios in the colder regions of Mars, is related to the isotopic fractionation occurring at condensation. We leverage this previous effort and present an updated implementation, using the modern version of the model, that remains in agreement with the older version. We explore the impact of the global dust storm (GDS) that occurred during Martian year 34 (MY34) on HDO. Our simulations indicate that HDO is on average 40% more abundant at 100 km during the MY34 GDS year than during a regular year, with likely large consequences for the escape flux of water that year. Plain Language Summary: HDO, the semi‐heavy isotope of water, when compared to water, is a good indicator of how much water has been escaping from the atmosphere of Mars over the ages. Ultimately, it can be used to estimate the past reservoir of water available on Mars in its early youth. Because HDO has a slightly higher molecular mass compared to H2O, condensation induces an enrichment of HDO in the ice phase compared with the vapor phase. This subsequently causes spatial and temporal variations of the deuterium to hydrogen ratio. We use a global circulation model to simulate the HDO cycle in the atmosphere. Our model is an upgrade of the previous model presented in Montmessin et al. (2005, Journal of Geophysical Research, 110(E3), E10004. doi:10.1029/2004JE002357). We then simulate the effect of the global dust storm that affected Mars during the summer of 2018, and show that it should have had a strong impact on the vertical distribution of HDO, allowing it to reach higher altitudes. Such simulations are intended to be compared with observations from the Trace Gas Orbiter, currently in orbit around Mars. Key Points: We reimplemented the HDO cycle in a more recent version of the Laboratoire de Météorologie Dynamique Mars global climate modelWe reproduce the observed gradient of the deuterium to hydrogen ratio between cold and warm regionsThe global dust storm of Martian year 34 has a strong effect on the vertical distribution of HDO [ABSTRACT FROM AUTHOR]

In situ measurements by an atmospheric entry probe allow for sounding and investigating atmospheric composition, structure and dynamics deep into the atmosphere of a Giant planet. In this paper, we describe an Atmospheric Structure Instrument (ASI) for an entry probe at Uranus and/or Neptune. The scientific objectives, the measurements and the expected results are discussed in the framework of a future opportunity for an NASA-ESA joint mission to the Ice Giant planets. [ABSTRACT FROM AUTHOR]

Highlights • First detection of cloud top ozone in Venus atmosphere (about 1000 times less than Earth). • Ozone presence is restricted to high latitudes (polewards of 50°) in both hemispheres. • Measurements are qualitatively supported by our 3D photochemical model. Abstract After the first sporadic detections of an ozone (O 3) nighttime layer in the 90–100 km altitude range (Montmessin et al., 2011), we report here the discovery of another, permanent ozone layer on Venus, restricted to high latitudes (polewards of 50° both N and S) and located at the upper cloud level near 70 km. This detection was performed during a reanalysis of the whole SPICAV-UV nadir dataset through UV absorption near 250 nm in the backscattered solar light. The O 3 volume mixing ratio peaks in the 10–20 ppbv range, yielding observable column densities in the 0.1–0.5 Dobson units (DU), comparable to nominal values on Mars but much smaller than for Earth (∼ 300 DU). These measurements are supported by our 3D-photochemical model coupled with the LMD-IPSL GCM (Lebonnois et al., 2010), which indicates that the ozone layer identified by SPICAV results from downward transport of O 2 (∼ 50 ppmv) molecules over the poles by the mean meridional circulation. Our findings do not contradict previous upper limits (< 2 ppmv) based on O 2 measurements (Mills, 1999), since they were restricted to lower latitudes only. [ABSTRACT FROM AUTHOR]

Recent observations of the Martian hydrogen corona in the UV H Ly-alpha emission by the Hubble Space Telescope (HST) (Clarke et al., 2014) and the SPICAM UV spectrometer on Mars Express (Chaffin et al., 2014) reported its rapid change by an order of magnitude over a short few months period in 2007 (MY28), which is inconsistent with the existing models. One proposed explanation of the observed increase of the coronal emission is that during the global dust storm water vapor from the lower atmosphere can be transported to higher altitudes, where its photodissociation rate by near-UV sunlight increases, providing an additional source of hydrogen for the upper atmosphere. In this work we study the water vapor vertical distribution in the middle atmosphere of Mars during the 2007 global dust storm based on solar occultation measurements by the SPICAM IR spectrometer onboard the Mars-Express spacecraft. The vertical profiles of H 2 O density and mixing ratio have been obtained for solar longitudes Ls = 255°–300° in MY28. In the Northern hemisphere from Ls = 268° to Ls = 285° the H 2 O density at altitudes of 60–80 km increased by an order of magnitude. During the dust storm the profiles extended up to 80 km, with an H 2 O density exceeding 10 10 molecules/cm 3 (mixing ratio ≥200 ppm). Two maxima of the H 2 O density were detected. The largest H 2 O densities observed at latitudes higher than 60°N, over Ls = 269°–275°, do not directly correlate with the aerosol loading and likely relate to the downwelling branch of the meridional circulation that was intensified during the dust storm, and transported water from the Southern hemisphere to high northern latitudes. The second smaller maximum coincides with the high dust loading at middle northern latitudes. The comparison with geographically close observations in the quiet Mars year MY32, when the H 2 O content in the Northern hemisphere did not exceed 2 × 10 10 molecules/cm 3 and 50 ppm at 60 km, showed that the global dust storm was a unique event. The situation was different in the Southern hemisphere. During the dust storm the water density at 50–80 km increased by a factor of 4–5 with a mixing ratio >100 ppm, well correlated with the aerosol vertical extension. A somewhat weaker increase of the H 2 O density by a factor of 2–3 with a mixing ratio > 100 ppm was also observed during MY32 starting from Ls = 260°, suggesting a seasonal repeatability. The observed amount of water at high altitudes in both hemispheres can produce a large increase in the H escape rate on a timescale of weeks, as was shown in the photochemical modeling by Chaffin et al. (2017). Future modeling would be necessary to separate the seasonal and the dust storm contributions to the hydrogen escape. [ABSTRACT FROM AUTHOR]

The Imaging Ultraviolet Spectrograph (IUVS) is one of nine science instruments aboard the Mars Atmosphere and Volatile and EvolutioN (MAVEN) spacecraft. MAVEN, launched in November 18, 2013 and arriving at Mars in September 2014, is designed to explore the planet's upper atmosphere and ionosphere and examine their interaction with the solar wind and solar ultraviolet radiation. IUVS is one of the most powerful spectrographs sent to another planet, with several key capabilities: (1) separate Far-UV & Mid-UV channels for stray light control, (2) a high resolution echelle mode to resolve deuterium and hydrogen emission, (3) internal instrument pointing and scanning capabilities to allow complete mapping and nearly-continuous operation, and (4) optimization for airglow studies. [ABSTRACT FROM AUTHOR]