LAPLACE: A mission to Europa and the Jupiter System for ESA's Cosmic Vision Programme

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Martian dust storm impact on atmospheric H₂O and D/H observed by ExoMars Trace Gas Orbiter

Global dust storms on Mars are rare but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere, primarily owing to solar heating of the dust. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars. Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes, as well as a decrease in the water column at low latitudes. Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H2O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals. The observed changes in H2O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere

No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere, which-given methane's lifetime of several centuries-predicts an even, well mixed distribution of methane. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally

Venus Evolution Through Time: Key Science Questions, Selected Mission Concepts and Future Investigations

In this work we discuss various selected mission concepts addressing Venus evolution through time. More specifically, we address investigations and payload instrument concepts supporting scientific goals and open questions presented in the companion articles of this volume. Also included are their related investigations (observations & modeling) and discussion of which measurements and future data products are needed to better constrain Venus’ atmosphere, climate, surface, interior and habitability evolution through time. A new fleet of Venus missions has been selected, and new mission concepts will continue to be considered for future selections. Missions under development include radar-equipped ESA-led EnVision M5 orbiter mission (European Space Agency 2021), NASA-JPL’s VERITAS orbiter mission (Smrekar et al. 2022a), NASA-GSFC’s DAVINCI entry probe/flyby mission (Garvin et al. 2022a). The data acquired with the VERITAS, DAVINCI, and EnVision from the end of this decade will fundamentally improve our understanding of the planet’s long term history, current activity and evolutionary path. We further describe future mission concepts and measurements beyond the current framework of selected missions, as well as the synergies between these mission concepts, ground-based and space-based observatories and facilities, laboratory measurements, and future algorithmic or modeling activities that pave the way for the development of a Venus program that extends into the 2040s (Wilson et al. 2022)

Comparison of current sheets in solar wind and planetary magnetospheres

International audienceCurrent sheets are structures that can be formed at the boundaries of different plasmas, magnetic fluxes and in areas with strong field gradients. When current sheets thicknesses become comparable with proton gyroradii they can play a key role of reservoirs of a free magnetic energy that can be released due to development of different current sheet instabilities. Such comparatively thin current sheets were relatively recently discovered by space missions in the magnetospheres of the Earth and planets, as well as in the solar wind. The development of a self-consistent current sheet theory in collisionless plasma has relatively long and dramatic history. The solution of the problem of thin current sheet structure and stability become possible in a frame of a kinetic quasi-adiabatic approach explaining multiscale embedded structure of thin current sheets and their metastability. We showed that the structure and stability of current structures are completely determined by the nonlinear dynamics of plasma particles within them. The similarity and difference of the current sheets in the solar wind and planetary magnetospheres are presented. Development of theoretical approaches to investigation of different current systems in space are discussed

Comparison of current sheets in solar wind and planetary magnetospheres

International audienceCurrent sheets are structures that can be formed at the boundaries of different plasmas, magnetic fluxes and in areas with strong field gradients. When current sheets thicknesses become comparable with proton gyroradii they can play a key role of reservoirs of a free magnetic energy that can be released due to development of different current sheet instabilities. Such comparatively thin current sheets were relatively recently discovered by space missions in the magnetospheres of the Earth and planets, as well as in the solar wind. The development of a self-consistent current sheet theory in collisionless plasma has relatively long and dramatic history. The solution of the problem of thin current sheet structure and stability become possible in a frame of a kinetic quasi-adiabatic approach explaining multiscale embedded structure of thin current sheets and their metastability. We showed that the structure and stability of current structures are completely determined by the nonlinear dynamics of plasma particles within them. The similarity and difference of the current sheets in the solar wind and planetary magnetospheres are presented. Development of theoretical approaches to investigation of different current systems in space are discussed

Comparison of current sheets in solar wind and planetary magnetospheres

International audienceCurrent sheets are structures that can be formed at the boundaries of different plasmas, magnetic fluxes and in areas with strong field gradients. When current sheets thicknesses become comparable with proton gyroradii they can play a key role of reservoirs of a free magnetic energy that can be released due to development of different current sheet instabilities. Such comparatively thin current sheets were relatively recently discovered by space missions in the magnetospheres of the Earth and planets, as well as in the solar wind. The development of a self-consistent current sheet theory in collisionless plasma has relatively long and dramatic history. The solution of the problem of thin current sheet structure and stability become possible in a frame of a kinetic quasi-adiabatic approach explaining multiscale embedded structure of thin current sheets and their metastability. We showed that the structure and stability of current structures are completely determined by the nonlinear dynamics of plasma particles within them. The similarity and difference of the current sheets in the solar wind and planetary magnetospheres are presented. Development of theoretical approaches to investigation of different current systems in space are discussed

Photoelectron distribution function over the illuminated part of the Moon

Photoelectron distribution functions in the near-surface layer over the lunar surface are obtained on the basis of the kinetic approach. The results are shown to depend strongly on the quantum yield of lunar regolith. It is demonstrated that photoelectrons with energies of about both 1 eV and 0.1 eV should be observed in the corresponding measurements