A Measurement of Water Vapour amid a Largely Quiescent Environment on Europa

Previous investigations proved the existence of local density enhancements in Europas atmosphere, advancing the idea of a possible origination from water plumes. These measurement strategies, however, were sensitive either to total absorption or atomic emissions, which limited the ability to assess the water content. Here we present direct searches for water vapour on Europa spanning dates from February 2016 to May 2017 with the Keck Observatory. Our global survey at infrared wavelengths resulted in non-detections on 16 out of 17 dates, with upper limits below the water abundances inferred from previous estimates. On one date (26 April 2016) we measured 2,095 658 tonnes of water vapour at Europas leading hemisphere. We suggest that the outgassing ls than previously estimated, with only rare localized events of stronger activity

HST/STIS Observations of Ganymede's Auroral Ovals at Eastern Elongation

We report on new Space Telescope Imaging Spectrograph (STIS) observations of Ganymede s auroral emissions obtained (to be obtained) during two visits with the Hubble Space Telescope (HST). The observations of the first visit, a five orbits, were obtained on November 19, 2010 and the second visit, also a five orbits, is scheduled for opposition in October/November 2011. We will present results of the full campaign, in case of a successful execution of the second visit. Our observations cover more than half a cycle of system III longitudes of Ganymede s positions within Jupiter s magnetosphere for each visit. We analyze the observations with respect to brightness and locations of Ganymede auroral ovals. Our goal is to set constrains on the interaction of Ganymede s mini-magnetosphere with Jupiter s magnetosphere, Ganymede s magnetic field and plasma environment, and if possible on Ganymede s neutral atmosphere

Ultraviolet and magnetic perspectives at Reiner Gamma and the implications for solar wind weathering

With the wealth of missions selected to visit the lunar surface in the decade ahead, preparatory investigations into surface conditions are underway to explore potential challenges and science returns during these missions. One such mission, Lunar Vertex, is slated to explore a much-anticipated region–the lunar swirl and magnetic anomaly known as Reiner Gamma. Lunar swirls are unique natural laboratories for exploring solar wind interactions with partially magnetized rocky bodies, and possess characteristics that have not yet been observed on any other body in the Solar System. This work aims to combine current magnetic mapping of Reiner Gamma with ultraviolet wavelength datasets, towards further understanding the sensitivities of ultraviolet measurements in regions that may be partially magnetically shielded from solar wind weathering and magnetospheric plasma populations. Observations and models herein are collected and derived from orbital sources and will be used for comparison to future orbital and surface observations of Reiner Gamma by Lunar Vertex

Mid-ultraviolet Hubble Observations of Europa and the Global Surface Distribution of SO₂

We present spatially resolved reflectance spectra of Europa’s surface in the wavelength range of 210–315 nm obtained by the Hubble Space Telescope Imaging Spectrograph in 2018 and 2019. These data provide the first high-quality, near-global spectral observations of Europa from 210 to 240 nm. They show that the reflectance of Europa’s leading, trailing, anti-Jovian, and sub-Jovian hemispheres is ∼5% near 210 nm, with varying spectral slopes across the mid-UV. This low albedo, even on the more “pristine” leading hemisphere, indicates a lack of the signature far-UV spectral edge characteristic of water ice. We detected and mapped a strong absorption feature at 280 nm that is consistent with an S–O bond that has previously been attributed to SO2 on the surface, hypothesized to be formed through radiolytic processing of Iogenic sulfur ions that have been preferentially emplaced on Europa’s trailing hemisphere by Jupiter’s magnetic field. Our models show that small inclusions of SO2 (0.1%) within the water ice are sufficient to produce the 280 nm feature without producing a feature at 4.07 μm, which has not been observed in ground-based spectral observations of Europa. This data set is the first to produce a spatially resolved, near-global map of the assumed SO2 feature, which is primarily concentrated near the apex of the trailing hemisphere and correlated with large-scale darker regions in both the visible and the ultraviolet. This distribution is consistent with “cold” exogenic sulfur ion bombardment on Europa

An attempt to detect transient changes in Io's SO2 and NaCl atmosphere

Io's atmosphere is predominately SO2 that is sustained by a combination of volcanic outgassing and sublimation. The loss from the atmosphere is the main mass source for Jupiter's large magnetosphere. Numerous previous studies attributed various transient phenomena in Io's environment and Jupiter's magnetosphere to a sudden change in the mass loss from the atmosphere supposedly triggered by a change in volcanic activity. Since the gas in volcanic plumes does not escape directly, such causal correlation would require a transient volcano-induced change in atmospheric abundance, which has never been observed so far. Here we report four observations of atmospheric SO2 and NaCl from the same hemisphere of Io, obtained with the IRAM NOEMA interferometer on 11 December 2016, 14 March, 6 and 29 April 2017. These observations are compared to measurements of volcanic hot spots and Io's neutral and plasma environment. We find a stable NaCl column density in Io's atmosphere on the four dates. The SO2 column density derived for December 2016 is about 30% lower compared to the SO2 column density found in the period of March to April 2017. This increase in SO2 from December 2016 to March 2017 might be related to increasing volcanic activity observed at several sites in spring 2017, but the stability of the volcanic trace gas NaCl and resulting decrease in NaCl/SO2 ratio do not support this interpretation. Observed dimmings in both the sulfur ion torus and Na neutral cloud suggest rather a decrease in mass loading in the period of increasing SO2 abundance. The dimming Na brightness and stable atmospheric NaCl furthermore dispute an earlier suggested positive correlation of the sodium cloud and the hot spot activity at Loki Patara, which considerably increased in this period. The environment of Io overall appears to be in a rather quiescent state, preventing further conclusions. Only Jupiter's aurora morphology underwent several short-term changes, which are apparently unrelated to Io's quiescent environment or the relatively stable atmosphere. © 2020 The AuthorsPeer reviewe