A rapid decrease of the hydrogen corona of Mars

Clarke, J. T.; Bertaux, Jean-Loup; Chaufray, J. Y.; Gladstone, G. R.; Quémerais, Éric; Wilson, J. K.; Bhattacharyya, Dolon

doi:10.1002/2014gl061803

Cited by 119 publications

(117 citation statements)

References 32 publications

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“…Clarke et al . [] used HST observations to derive exobase densities decreasing from 5 × 10 4 to 3.5 × 10 4 cm −3 for an exospheric temperature of 340 K for L S = 331–345 near solar minimum, a factor of 2 lower than our values for the same L S range in May 2015. Bhattacharyya et al .…”

Section: Derived Exospheric Hydrogen Distribution and Escape Ratesmentioning

confidence: 63%

“…Recent observations have revealed a high degree of variability in the hydrogen exosphere [ Chaffin et al ., ; Clarke et al ., , ; Yamauchi et al ., ; Bhattacharyya et al ., ; Romanelli et al ., ; Rahmati et al ., ; Halekas et al ., ], with higher column densities typically observed near perihelion and lower densities near aphelion. However, many of these observations have incomplete temporal coverage, and uncertainties in data inversion make it challenging to translate observations of seasonal variability into quantitative estimates of escape flux.…”

Section: Introductionmentioning

confidence: 99%

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Seasonal variability of the hydrogen exosphere of Mars

2017

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The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission measures both the upstream solar wind and collisional products from energetic neutral hydrogen atoms that precipitate into the upper atmosphere after their initial formation by charge exchange with exospheric hydrogen. By computing the ratio between the densities of these populations, we derive a robust measurement of the column density of exospheric hydrogen upstream of the Martian bow shock. By comparing with Chamberlain‐type model exospheres, we place new constraints on the structure and escape rates of exospheric hydrogen, derived from observations sensitive to a different and potentially complementary column from most scattered sunlight observations. Our observations provide quantitative estimates of the hydrogen exosphere with nearly complete temporal coverage, revealing order of magnitude seasonal changes in column density and a peak slightly after perihelion, approximately at southern summer solstice. The timing of this peak suggests either a lag in the response of the Martian atmosphere to solar inputs or a seasonal effect driven by lower atmosphere dynamics. The high degree of seasonal variability implied by our observations suggests that the Martian atmosphere and the thermal escape of light elements depend sensitively on solar inputs.

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Section: Derived Exospheric Hydrogen Distribution and Escape Ratesmentioning

confidence: 63%

Section: Introductionmentioning

confidence: 99%

Seasonal variability of the hydrogen exosphere of Mars

2017

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“…In the course of constraining the H escape flux, observations of Mars by Hubble Space Telescope (HST) in October–November 2007 identified a 40% decrease in intensity of scattered solar Lyman α by Martian exospheric hydrogen in ~4 weeks [ Clarke et al , ]. This trend, also observed by Mars Express over several months yielded up to an order‐of‐magnitude change in hydrogen escape flux [ Chaffin et al , ].…”

Section: Introductionmentioning

confidence: 75%

A strong seasonal dependence in the Martian hydrogen exosphere

Bhattacharyya

Clarke

Bertaux

et al. 2015

Geophys. Res. Lett.

104

108

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Hubble Space Telescope and Mars Express observed unexpected rapid changes in the Martian hydrogen exosphere involving a decrease in scattered Lyman α intensity in fall 2007 (solar longitude, Ls = 331°–345°). These changes detected were speculated to be a combination of seasonal variation and/or dust storms and lower atmospheric dynamics. Here we present Hubble Space Telescope observations of Mars in 2014 over a broad range of heliocentric distances and seasons (Ls = 138°–232°) which indicate a factor of ~3.5 change in Martian Lyman α brightness associated with a factor of ~5.4 variation of hydrogen escape flux in the absence of global dust storms and significant solar variability. We thus conclude that seasonal effects have a strong influence on the hydrogen exosphere, which in turn has major implications for the processes that control water supply to the Martian upper atmosphere and the history of water escape from Mars.

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“…Interestingly, observational evidence of a strong seasonal dependence in the hydrogen exosphere of Mars has been recently reported in Clarke et al [], Chaffin et al [], and Bhattacharyya et al [], based on Hubble Space Telescope and MEX scattered Lyman α brightness observations. In agreement with these observations, a large decrease in the median penetrating proton density [ Halekas et al , ] derived from MAVEN Solar Wind Ion Analyzer (SWIA) [ Halekas et al , ] measurements is observed during the MAVEN mission (lower density values for larger heliocentric distances) and also indicates a high level of seasonal variability in the Martian H exosphere.…”

Section: Discussionmentioning

confidence: 94%

Proton cyclotron waves occurrence rate upstream from Mars observed by MAVEN: Associated variability of the Martian upper atmosphere

et al. 2016

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Measurements provided by the Magnetometer and the Extreme Ultraviolet Monitor (EUVM) on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft together with atomic H exospheric densities derived from numerical simulations are studied for the time interval from October 2014 up to March 2016. We determine the proton cyclotron waves (PCWs) occurrence rate observed upstream from Mars at different times. We also study the relationship with temporal variabilities of the high‐altitude Martian hydrogen exosphere and the solar EUV flux reaching the Martian environment. We find that the abundance of PCWs is higher when Mars is close to perihelion and decreases to lower and approximately constant values after the Martian Northern Spring Equinox. We also conclude that these variabilities cannot be associated with biases in MAVEN's spatial coverage or changes in the background magnetic field orientation. Higher H exospheric densities on the Martian dayside are also found when Mars is closer to perihelion, as a result of changes in the thermospheric response to variability in the ultraviolet flux reaching Mars at different orbital distances. A consistent behavior is also observed in the analyzed daily irradiances measured by the MAVEN EUVM. The latter trends point toward an increase in the planetary proton densities upstream from the Martian bow shock near perihelion. These results then suggest a method to indirectly monitor the variability of the H exosphere up to very high altitudes during large time intervals (compared to direct measurements of neutral particles), based on the observed abundance of PCWs.

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A rapid decrease of the hydrogen corona of Mars

Cited by 119 publications

References 32 publications

Seasonal variability of the hydrogen exosphere of Mars

Seasonal variability of the hydrogen exosphere of Mars

A strong seasonal dependence in the Martian hydrogen exosphere

Proton cyclotron waves occurrence rate upstream from Mars observed by MAVEN: Associated variability of the Martian upper atmosphere

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