A strong seasonal dependence in the Martian hydrogen exosphere

Bhattacharyya, Dolon; Clarke, J. T.; Bertaux, Jean-Loup; Chaufray, Jean‐Yves; Mayyasi, Majd

doi:10.1002/2015gl065804

Cited by 104 publications

(142 citation statements)

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“…A neutral H, H 2 , and O Chamberlain (1963) exosphere is generated (Halekas, 2017) using exobase densities and temperatures of 1 × 10 6 cm −3 and 300 K, respectively, values that are in agreement with previously reported observations (e.g., Anderson & Hord, 1971;Bhattacharyya et al, 2015;Chaufray et al, 2008;Chaffin et al, 2015;Feldman et al, 2011). A neutral H, H 2 , and O Chamberlain (1963) exosphere is generated (Halekas, 2017) using exobase densities and temperatures of 1 × 10 6 cm −3 and 300 K, respectively, values that are in agreement with previously reported observations (e.g., Anderson & Hord, 1971;Bhattacharyya et al, 2015;Chaufray et al, 2008;Chaffin et al, 2015;Feldman et al, 2011).…”

Section: Simulations Of Charge Exchange In the Upstream Regionsupporting

confidence: 88%

The Modulation of Solar Wind Hydrogen Deposition in the Martian Atmosphere by Foreshock Phenomena

et al. 2019

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The neutral exosphere of Mars extends far upstream beyond the bow shock, and as a result, solar wind protons can charge exchange with this neutral exosphere to produce energetic neutral atoms. Energetic neutral atoms produced directly upstream of Mars will precipitate into the Martian dayside atmosphere, where some fraction can undergo a charge stripping reaction and can be observed as “penetrating protons.” Clear, quasiperiodic modulations in penetrating proton densities are observed during certain Mars Atmosphere and Volatile EvolutioN (MAVEN) periapsis passes, and we show that these modulations occur during radial interplanetary magnetic field conditions. During such times, the region sunward of Mars is defined by quasi‐parallel shock conditions, generating foreshock structures characterized by enhancements in magnetic field strength, enhancements in proton density, and deceleration and deflection of the solar wind flow. These structures are observed at time cadences equal to the modulation of penetrating proton densities at periapsis. Particle tracing simulations show that the convection of these structures with the solar wind leads to localized enhancements in the rate of charge exchange upstream of the shock, producing the observed temporal variations in penetrating proton densities at periapsis. The observation of modulated penetrating proton densities at periapsis can thus be used to infer the existence of radial interplanetary magnetic field conditions upstream of the bow shock at Mars at times when MAVEN does not sample the upstream solar wind.

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Section: Simulations Of Charge Exchange In the Upstream Regionsupporting

confidence: 88%

The Modulation of Solar Wind Hydrogen Deposition in the Martian Atmosphere by Foreshock Phenomena

et al. 2019

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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%

“…Consequently, Yamauchi et al [] concluded that even though the variation in solar UV flux has a major effect on the formation of pickup ions, it is not the only contributing component. Similarly, Bhattacharyya et al [] also concluded that the observed seasonal changes in the neutral H exospheric densities cannot be explained only on the basis of changes in the incident EUV flux. Moreover, the supplying process of H to the exosphere of Mars through diffusion of molecular H 2 from lower altitudes is slow, not capable of explaining observed short‐term changes in the H density.…”

Section: Discussionmentioning

confidence: 99%

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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“…SWIA observations also confirm a strong seasonal variation of the hydrogen corona [ Yamauchi et al ., ; Chaffin et al ., ; Bhattacharyya et al ., ], with much larger (an order of magnitude) amplitude than the heliocentric variation in EUV input. A longer baseline of observations afforded by additional MAVEN extended missions could reveal a solar cycle component to the hydrogen variability or interannual variations in the seasonal variation of the hydrogen corona.…”

Section: Discussionmentioning

confidence: 99%

“…As shown in Figure (third panel), the charge exchange rate upstream of the shock must vary with time, since we observe a large decrease in the median penetrating proton density over the MAVEN mission, in addition to the expected solar wind variability. This decline most likely primarily reflects changes in the Martian exosphere, which we know to have a high degree of seasonal variability, thanks to spectroscopic observations [ Chaffin et al ., ; Bhattacharyya et al ., ] and pickup ion measurements [ Yamauchi et al ., ]. Given the results of Kallio et al .…”

Section: Solar Energy Inputs To the Martian Systemmentioning

confidence: 98%

Structure, dynamics, and seasonal variability of the Mars‐solar wind interaction: MAVEN Solar Wind Ion Analyzer in‐flight performance and science results

et al. 2017

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We report on the in‐flight performance of the Solar Wind Ion Analyzer (SWIA) and observations of the Mars‐solar wind interaction made during the Mars Atmosphere and Volatile EvolutioN (MAVEN) prime mission and a portion of its extended mission, covering 0.85 Martian years. We describe the data products returned by SWIA and discuss the proper handling of measurements made with different mechanical attenuator states and telemetry modes, and the effects of penetrating and scattered backgrounds, limited phase space coverage, and multi‐ion populations on SWIA observations. SWIA directly measures solar wind protons and alpha particles upstream from Mars. SWIA also provides proxy measurements of solar wind and neutral densities based on products of charge exchange between the solar wind and the hydrogen corona. Together, upstream and proxy observations provide a complete record of the solar wind experienced by Mars, enabling organization of the structure, dynamics, and ion escape from the magnetosphere. We observe an interaction that varies with season and solar wind conditions. Solar wind dynamic pressure, Mach number, and extreme ultraviolet flux all affect the bow shock location. We confirm the occurrence of order‐of‐magnitude seasonal variations of the hydrogen corona. We find that solar wind Alfvén waves, which provide an additional energy input to Mars, vary over the mission. At most times, only weak mass loading occurs upstream from the bow shock. However, during periods with near‐radial interplanetary magnetic fields, structures consistent with Short Large Amplitude Magnetic Structures and their wakes form upstream, dramatically reconfiguring the Martian bow shock and magnetosphere.

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A strong seasonal dependence in the Martian hydrogen exosphere

Cited by 104 publications

References 50 publications

The Modulation of Solar Wind Hydrogen Deposition in the Martian Atmosphere by Foreshock Phenomena

The Modulation of Solar Wind Hydrogen Deposition in the Martian Atmosphere by Foreshock Phenomena

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

Structure, dynamics, and seasonal variability of the Mars‐solar wind interaction: MAVEN Solar Wind Ion Analyzer in‐flight performance and science results

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