Planetary surfaces

Abstract:

Hydrogen chloride gas was recently discovered in the atmosphere of Mars during southern summer seasons. Its connection with potential chlorine reservoirs and the related atmospheric chemistry is now of particular interest and actively studied. Measurements by the Atmospheric Chemistry Suite mid-infrared channel (ACS MIR) on the ExoMars Trace Gas Orbiter allow us to measure the ratio of hydrogen chloride two stable isotopologues, H35Cl and H37Cl. This work describes the observation, processing technique, and derived values for the chloride isotope ratio. Unlike other volatiles in the Martian atmosphere, because it is enriched with heavier isotopes, the δ37Cl is measured to be - 7 ± 20°, which is almost indistinguishable from the terrestrial ratio for chlorine. This value agrees with available measurements of the surface materials on Mars. We conclude that chlorine in observed HCl likely originates from dust and is not involved in any long-term, surface-atmosphere cycle.

Abstract:

Ultraviolet spectral imaging has been a powerful tool to investigate the cloud top of Venus, allowing for measurement of several minor gases (especially SO , SO, O ), 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. 2 3

Abstract:

Over the last decade, the vector-apodizing phase plate (vAPP) coronagraph has been developed from concept to on-sky application in many high-contrast imaging systems on 8 m class telescopes. The vAPP is a geometric-phase patterned coronagraph that is inherently broadband, and its manufacturing is enabled only by direct-write technology for liquid-crystal patterns. The vAPP generates two coronagraphic point spread functions (PSFs) that cancel starlight on opposite sides of the PSF and have opposite circular polarization states. The efficiency, that is, the amount of light in these PSFs, depends on the retardance offset from a half-wave of the liquid-crystal retarder. Using different liquid-crystal recipes to tune the retardance, different vAPPs operate with high efficiencies (${\gt}96\%$) in the visible and thermal infrared (0.55 µm to 5 µm). Since 2015, seven vAPPs have been installed in a total of six different instruments, including Magellan/MagAO, Magellan/MagAO-X, Subaru/SCExAO, and LBT/LMIRcam. Using two integral field spectrographs installed on the latter two instruments, these vAPPs can provide low-resolution spectra (${\rm{R}} \sim 30$) between 1 µm and 5 µm. We review the design process, development, commissioning, on-sky performance, and first scientific results of all commissioned vAPPs. We report on the lessons learned and conclude with perspectives for future developments and applications.