Space instrumentation

Abstract:

Heterogeneous electrochemistry induced by Martian dust activity is an important type of atmosphere-surface interaction that affects geochemical processes at the Martian surface and in the Martian atmosphere. We have experimentally demonstrated that heterogeneous electrochemistry stimulated by mid-strength dust events can decompose common chloride salts, which is accompanied by the release of chlorine atoms into the atmosphere and the generation of (per)chlorates (chlorates and perchlorates) and carbonates. In this study, we present quantitative analyses on the above products from 26 heterogeneous electrochemical experiments on chloride salts. Based on these quantifications, our calculation indicates that such atmosphere-surface interaction during a portion of Amazonian period could accumulate the observed abundance of (per)chlorates, carbonates, and HCl by landed and orbital missions, and thus can be considered as a major driving force of the global chlorine-cycle on Mars. This study emphasizes the importance of measuring the electrical properties of dust activity on Mars.

Abstract:

On Mars, condensation is the major factor constraining the vertical distribution of water vapor. Recent measurements of water and temperature profiles showed that water can be strongly supersaturated at and above the level where clouds form during the aphelion and perihelion seasons. Since 2018, the near-infrared spectrometer (NIR) of the Atmospheric Chemistry Suite onboard the Trace Gas Orbiter has measured H2O and temperature profiles using solar occultation in the infrared from below 10 to 100 km of altitude. Here, we provide the first long-term monitoring of the water saturation state. The survey spans 2 Martian years from Ls = 163° of MY34 to Ls = 170° of MY36. We found that water is often supersaturated above aerosol layers. In the aphelion season, the water mixing ratio above 40 km in the mid-to-high latitudes was below 3 ppmv and yet is found to be supersaturated. Around the perihelion, water is also supersaturated above 60 km with a mixing ratio of 30–50 ppmv. Stronger saturation is observed during the dusty season in MY35 compared to what was observed in MY34 during the Global Dust Storm and around the perihelion. Saturation varied between the evening and morning terminators in response to temperature modulation imparted by thermal tides. Although water vapor is more abundant in the evening, colder morning temperatures induce a daily peak of saturation. This data set establishes a new paradigm for water vapor on Mars, revealing that supersaturation is nearly ubiquitous, particularly during the dust season, thereby promoting water escape on an annual average.

Abstract:

On January 31, 2011, the remote-sensing instruments onboard the Cassini spacecraft (UVIS (Ultraviolet Imaging Spectrograph; ISS (Imaging Science Subsystem); VIMS (Visual and Infrared Mapping Spectrometer) and CIRS (Composite Infrared Spectrometer)) observed Helene, Dione's leading Lagrangian moon. We report here on the photometric characteristics of Helene between 0.11 μm and 5.2 μm. We find that Helene's spectrum is dominated by the signature of water-ice and we retrieve a grain size of 3.4 μm in the ultraviolet. At all wavelengths, Helene shows signs of being a relatively fresh surface less affected by space weathering effects than other observed surfaces in the Saturn system. We present the first phase curve of Helene at 0.61 μm and place our ultraviolet and near-IR results in a wider spectral context toward a better understanding of Helene's surface evolution. Previous studies suggested that either a recent impact on Helene or an asymmetric flux of E-ring particles could explain the satellite high surface brightness (Hedman et al., 2020). Results from this study favor the impactor hypothesis to explain Helene's photometric behavior.