Unexpected variability of Martian hydrogen escape

Chaffin, Michael; Chaufray, Jean‐Yves; Stewart, Ian; Montmessin, Franck; Schneider, Nicholas M.; Bertaux, Jean-Loup

doi:10.1002/2013gl058578

Cited by 156 publications

(151 citation statements)

References 40 publications

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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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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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“…For instance, given the very high solar wind flux on the order of 8 × 10 8 cm À2 s À1 during the 8 March 2015 CME of Figure 4, we can infer solar wind hydrogen deposition in the atmosphere on the order of 2 × 10 7 cm À2 s À1 , comparable to the thermal escape flux of hydrogen for at least some time periods [Chaffin et al, 2014]. Early in the solar system's history, solar wind flux and/or solar activity were likely stronger, potentially making solar wind accretion a more important source of hydrogen and perhaps even affecting the Deuterium/Hydrogen (D/H) ratio of the atmosphere.…”

Section: /2015gl064693mentioning

confidence: 93%

MAVEN observations of solar wind hydrogen deposition in the atmosphere of Mars

Halekas

Lillis

Mitchell

et al. 2015

Geophysical Research Letters

130

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Mars Atmosphere and Volatile EvolutioN mission (MAVEN) observes a tenuous but ubiquitous flux of protons with the same energy as the solar wind in the Martian atmosphere. During high flux intervals, we observe a corresponding negative hydrogen population. The correlation between penetrating and solar wind fluxes, the constant energy, and the lack of a corresponding charged population at intermediate altitudes implicate products of hydrogen energetic neutral atoms from charge exchange between the upstream solar wind and the exosphere. These atoms, previously observed in neutral form, penetrate the magnetosphere unaffected by electromagnetic fields (retaining the solar wind velocity), and some fraction reconvert to charged form through collisions with the atmosphere. MAVEN characterizes the energy and angular distributions of both penetrating and backscattered particles, potentially providing information about the solar wind, the hydrogen corona, and collisional interactions in the atmosphere. The accretion of solar wind hydrogen may provide an important source term to the Martian atmosphere over the planet's history.

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“…Jeans Escape Jeans escape rates can be determined from knowledge of the neutral composition and temperature at and near the exobase, as was done using Mariner 9 and Mars Express ultraviolet observations (Anderson and Hord 1971;Chaufray et al 2008;Chaffin et al 2014). With neutral atoms having a temperature of ∼ 250 K (0.02 eV for H, compared to ∼ 0.1 eV escape energy) at the exobase, Jeans escape is significant for the loss of H, deuterium (D), and He.…”

Section: Brief Summary Of Mechanisms For Atmospheric Lossmentioning

confidence: 99%

The Mars Atmosphere and Volatile Evolution (MAVEN) Mission

Jakosky

Lin

Grebowsky³

et al. 2015

Space Sci Rev

632

593

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International audienceThe MAVEN spacecraft launched in November 2013, arrived at Mars in September 2014, and completed commissioning and began its one-Earth-year primary science mission in November 2014. The orbiter’s science objectives are to explore the interactions of the Sun and the solar wind with the Mars magnetosphere and upper atmosphere, to determine the structure of the upper atmosphere and ionosphere and the processes controlling it, to determine the escape rates from the upper atmosphere to space at the present epoch, and to measure properties that allow us to extrapolate these escape rates into the past to determine the total loss of atmospheric gas to space through time. These results will allow us to determine the importance of loss to space in changing the Mars climate and atmosphere through time, thereby providing important boundary conditions on the history of the habitability of Mars. The MAVEN spacecraft contains eight science instruments (with nine sensors) that measure the energy and particle input from the Sun into the Mars upper atmosphere, the response of the upper atmosphere to that input, and the resulting escape of gas to space. In addition, it contains an Electra relay that will allow it to relay commands and data between spacecraft on the surface and Earth

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Unexpected variability of Martian hydrogen escape

Cited by 156 publications

References 40 publications

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

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

MAVEN observations of solar wind hydrogen deposition in the atmosphere of Mars

The Mars Atmosphere and Volatile Evolution (MAVEN) Mission

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