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See detailMartian dust storm impact on atmospheric H 2 O and D/H observed by ExoMars Trace Gas Orbiter
Vandaele, A. C.; Korablev, O.; Daerden, F. et al

in Nature (2019), 568

Global dust storms on Mars are rare 1,2 but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere 3 , primarily owing to ... [more ▼]

Global dust storms on Mars are rare 1,2 but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere 3 , primarily owing to solar heating of the dust 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 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 5,6 , as well as a decrease in the water column at low latitudes 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 2 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 H 2 O 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 3 . The observed changes in H 2 O 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. © 2019, The Author(s), under exclusive licence to Springer Nature Limited. [less ▲]

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See detailNo detection of methane on Mars from early ExoMars Trace Gas Orbiter observations
Korablev, O.; Vandaele, A. C.; Montmessin, F. et al

in Nature (2019), 568

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today 1 . A number of different measurements of methane show evidence of ... [more ▼]

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today 1 . A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations 2–5 . These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere 6,7 , which—given methane’s lifetime of several centuries—predicts an even, well mixed distribution of methane 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 2,4 . We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater 4 would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally. [less ▲]

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See detailA warm layer in Venus' cryosphere and high-altitude measurements of HF, HCl, H[SUB]2[/SUB]O and HDO
Bertaux, Jean-Loup; Vandaele, Ann-Carine; Korablev, Oleg et al

in Nature (2007), 450

Venus has thick clouds of H[SUB]2[/SUB]SO[SUB]4[/SUB] aerosol particles extending from altitudes of 40 to 60km. The 60-100km region (the mesosphere) is a transition region between the 4day retrograde ... [more ▼]

Venus has thick clouds of H[SUB]2[/SUB]SO[SUB]4[/SUB] aerosol particles extending from altitudes of 40 to 60km. The 60-100km region (the mesosphere) is a transition region between the 4day retrograde superrotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere (above 100km), which has upwelling over the subsolar point and transport to the nightside. The mesosphere has a light haze of variable optical thickness, with CO, SO[SUB]2[/SUB], HCl, HF, H[SUB]2[/SUB]O 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 60km. Here we report the detection of an extensive layer of warm air at altitudes 90-120km 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 100km. We also measured the mesospheric distributions of HF, HCl, H[SUB]2[/SUB]O and HDO. HCl is less abundant than reported 40years ago. HDO/H[SUB]2[/SUB]O is enhanced by a factor of ~2.5 with respect to the lower atmosphere, and there is a general depletion of H[SUB]2[/SUB]O around 80-90km for which we have no explanation. [less ▲]

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