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Global dust storms on Mars are rare.sup.1,2 but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere.sup.3, primarily owing to solar heating of the dust.sup.3. 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.sup.4. 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.sup.5,6, as well as a decrease in the water column at low latitudes.sup.7,8. 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.sub.2O 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 H.sub.2O 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.sup.3. The observed changes in H.sub.2O 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. High-resolution measurements of Martian atmospheric dust, water and semiheavy water, obtained by the ExoMars Trace Gas Orbiter during a global dust storm on Mars, are reported., Author(s): Ann Carine Vandaele [sup.1] , Oleg Korablev [sup.2] , Frank Daerden [sup.1] , Shohei Aoki [sup.1] , Ian R. Thomas [sup.1] , Francesca Altieri [sup.3] , Miguel López-Valverde [sup.4] [...]

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today.sup.1. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations.sup.2-5. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere.sup.6,7, which--given methane's lifetime of several centuries--predicts an even, well mixed distribution of methane.sup.1,6,8. 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.sup.2,4. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater.sup.4 would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally. Highly sensitive measurements of the atmosphere of Mars with the ExoMars Trace Gas Orbiter do not detect any methane over a range of latitudes in both hemispheres, in contrast to previous local or remote detections., Author(s): Oleg Korablev [sup.1] , Ann Carine Vandaele [sup.2] , Franck Montmessin [sup.3] , Anna A. Fedorova [sup.1] , Alexander Trokhimovskiy [sup.1] , François Forget [sup.4] , Franck Lefèvre [sup.3] [...]

Author(s): Jean-Loup Bertaux [1, 2, 5]; Ann-Carine Vandaele [3]; Oleg Korablev [4]; E. Villard [1, 2, 5]; A. Fedorova [4]; D. Fussen [3]; E. Quémerais [1, 2, 5]; D. Belyaev [...]

The surname of author Cathy Quantin-Nataf was misspelled 'Quantin-Nata', authors Ehouarn Millour and Roland Young were missing from the ACS and NOMAD Science Teams list, and minor changes have been made to the author and affiliation lists; see accompanying Amendment. These errors have been corrected online., Author(s): Oleg Korablev [sup.1] , Ann Carine Vandaele [sup.2] , Franck Montmessin [sup.3] , Anna A. Fedorova [sup.1] , Alexander Trokhimovskiy [sup.1] , François Forget [sup.4] , Franck Lefèvre [sup.3] [...]

The surname of author Cathy Quantin-Nataf was misspelled 'Quantin-Nata' , authors Ehouarn Millour and Roland Young were missing from the ACS Science Team list, and minor changes have been made to the author and affiliation lists; see accompanying Amendment. These errors have been corrected online., Author(s): Ann Carine Vandaele [sup.1] , Oleg Korablev [sup.2] , Frank Daerden [sup.1] , Shohei Aoki [sup.1] , Ian R. Thomas [sup.1] , Francesca Altieri [sup.3] , Miguel López-Valverde [sup.4] [...]

Global dust storms on Mars are rare1,2 but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere3, primarily owing to solar heating of the dust3. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars4. 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 latitudes5,6, as well as a decrease in the water column at low latitudes7,8. 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/H2O 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 crystals3. 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. High-resolution measurements of Martian atmospheric dust, water and semiheavy water, obtained by the ExoMars Trace Gas Orbiter during a global dust storm on Mars, are reported. [ABSTRACT FROM AUTHOR]

Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60 km. The 60–100 km region (the mesosphere) is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar–antisolar circulation in the thermosphere (above 100 km), which has upwelling over the subsolar point and transport to the nightside. The mesosphere has a light haze of variable optical thickness, with CO, SO2, HCl, HF, H2O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km. Here we report the detection of an extensive layer of warm air at altitudes 90–120 km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the ‘cryosphere’ above 100 km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40 years ago. HDO/H2O is enhanced by a factor of ∼2.5 with respect to the lower atmosphere, and there is a general depletion of H2O around 80–90 km for which we have no explanation. [ABSTRACT FROM AUTHOR]