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Bruce M. Jakosky - One of the best experts on this subject based on the ideXlab platform.
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dust storm enhanced gravity wave activity in the martian thermosphere observed by maven and implication for atmospheric escape
2021Co-Authors: Erdal Yigit, Alexander S Medvedev, Mehdi Benna, Bruce M. JakoskyAbstract:Lower atmospheric global dust storms affect the small- and large-scale weather and variability of the whole Martian Atmosphere. Analysis of the CO$_2$ density data from the Neutral Gas and Ion Mass Spectrometer instrument (NGIMS) on board NASA's Mars Atmosphere Volatile EvolutioN (MAVEN) spacecraft show a remarkable increase of GW-induced density fluctuations in the thermosphere during the 2018 major dust storm with distinct latitude and local time variability. The mean thermospheric GW activity increases by a factor of two during the storm event. The magnitude of relative density perturbations is around 20% on average and 40% locally. One and a half months later, the GW activity gradually decreases. Enhanced temperature disturbances in the Martian thermosphere can facilitate atmospheric escape. For the first time, we estimate that, for a 20% and 40% GW-induced disturbances, the net increase of Jeans escape flux of hydrogen is a factor of 1.3 and 2, respectively.
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global circulation of Mars upper Atmosphere
2019Co-Authors: Erdal Yigit, Mehdi Benna, S W Bougher, P R Mahaffy, Yuni Lee, Kali Roeten, Bruce M. JakoskyAbstract:The thermosphere of Mars is the interface through which the planet is continuously losing its reservoir of atmospheric volatiles to space. The structure and dynamics of the thermosphere is driven by a global circulation that redistributes the incident energy from the Sun. We report mapping of the global circulation in the thermosphere of Mars with the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. The measured neutral winds reveal circulation patterns simpler than those of Earth that persist over changing seasons. The winds exhibit pronounced correlation with the underlying topography owing to orographic gravity waves.
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ionospheric ambipolar electric fields of Mars and venus comparisons between theoretical predictions and direct observations of the electric potential drop
2019Co-Authors: David L Mitchell, L Andersson, J. M. Grebowsky, Glyn Collinson, A Glocer, R A Frahm, Bruce M. JakoskyAbstract:We test the hypothesis that their dominant driver of a planetary ambipolar electric field is the ionospheric electron pressure gradient (∇Pe). The ionospheres of Venus and Mars are mapped using Langmuir probe measurements from NASA's Pioneer Venus Orbiter (PVO) and Mars Atmosphere and Volatile Evolution (MAVEN) missions. We then determine the component of the ionospheric potential drop that can be explained by the electron pressure gradient drop along a simple draped field line. At Mars, this calculation is consistent with the mean potential drops measured statistically by MAVEN. However, at Venus, contrary to our current understanding, the thermal electron pressure gradient alone cannot explain Venus' strong ambipolar field. These results strongly motivate a return to Venus with a comprehensive plasmas and fields package, similar to that on MAVEN, to investigate the physics of atmospheric escape at Earth's closest analog.
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unique non earthlike meteoritic ion behavior in upper Atmosphere of Mars
2017Co-Authors: J. M. Grebowsky, Mehdi Benna, P R Mahaffy, G Collinson, John M C Plane, Bruce M. JakoskyAbstract:Interplanetary dust particles have long been expected to produce permanent ionospheric metal ion layers at Mars, as on Earth, but the two environments are so different that uncertainty existed as to whether terrestrial-established understanding would apply to Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission made the first in situ detection of the continuous presence of Na+, Mg+, and Fe+ at Mars and indeed revealed non-Earthlike features/processes. There is no separation of the light Mg+ and the heavy Fe+ with increasing altitude as expected for gravity control. The metal ions are well-mixed with the neutral Atmosphere at altitudes where no mixing process is expected. Isolated metal ion layers mimicking Earth's sporadic E layers occur despite the lack of a strong magnetic field as required at Earth. Further, the metal ion distributions are coherent enough to always show atmospheric gravity wave signatures. All features and processes are unique to Mars.
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Mars atmospheric history derived from upper Atmosphere measurements of 38ar 36ar
2017Co-Authors: Bruce M. Jakosky, M K Elrod, P Mahaffy, Mehdi Benna, S. Stone, R V Yelle, M Slipski, N AlsaeedAbstract:The history of Mars’ Atmosphere is important for understanding the geological evolution and potential habitability of the planet. We determine the amount of gas lost to space through time using measurements of the upper-atmospheric structure made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. We derive the structure of 38Ar/36Ar between the homopause and exobase altitudes. Fractionation of argon occurs as a result of loss of gas to space by pickup-ion sputtering, which preferentially removes the lighter atom. The measurements require that 66% of the atmospheric argon has been lost to space. Thus, a large fraction of Mars’ atmospheric gas has been lost to space, contributing to the transition in climate from an early, warm, wet environment to today’s cold, dry Atmosphere.
Mehdi Benna - One of the best experts on this subject based on the ideXlab platform.
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dust storm enhanced gravity wave activity in the martian thermosphere observed by maven and implication for atmospheric escape
2021Co-Authors: Erdal Yigit, Alexander S Medvedev, Mehdi Benna, Bruce M. JakoskyAbstract:Lower atmospheric global dust storms affect the small- and large-scale weather and variability of the whole Martian Atmosphere. Analysis of the CO$_2$ density data from the Neutral Gas and Ion Mass Spectrometer instrument (NGIMS) on board NASA's Mars Atmosphere Volatile EvolutioN (MAVEN) spacecraft show a remarkable increase of GW-induced density fluctuations in the thermosphere during the 2018 major dust storm with distinct latitude and local time variability. The mean thermospheric GW activity increases by a factor of two during the storm event. The magnitude of relative density perturbations is around 20% on average and 40% locally. One and a half months later, the GW activity gradually decreases. Enhanced temperature disturbances in the Martian thermosphere can facilitate atmospheric escape. For the first time, we estimate that, for a 20% and 40% GW-induced disturbances, the net increase of Jeans escape flux of hydrogen is a factor of 1.3 and 2, respectively.
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global circulation of Mars upper Atmosphere
2019Co-Authors: Erdal Yigit, Mehdi Benna, S W Bougher, P R Mahaffy, Yuni Lee, Kali Roeten, Bruce M. JakoskyAbstract:The thermosphere of Mars is the interface through which the planet is continuously losing its reservoir of atmospheric volatiles to space. The structure and dynamics of the thermosphere is driven by a global circulation that redistributes the incident energy from the Sun. We report mapping of the global circulation in the thermosphere of Mars with the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. The measured neutral winds reveal circulation patterns simpler than those of Earth that persist over changing seasons. The winds exhibit pronounced correlation with the underlying topography owing to orographic gravity waves.
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Seasonal Variability of Deuterium in the Upper Atmosphere of Mars
2019Co-Authors: M. Mayyasi, Roger V. Yelle, Mehdi Benna, Jean-yves Chaufray, John Clarke, Dolon Bhattacharyya, Paul Mahaffy, S. Stone, Edward Thiemann, M. S. ChaffinAbstract:Measurements by multiple Mars Atmosphere and Volatile Evolution mission instruments, obtained between November 2014 and November 2017, are analyzed to produce deuterium properties in the upper Atmosphere of Mars. We show here, for the first time, the seasonal distribution and variability of D densities, temperatures, and estimated Jeans escape rates at the exobase (200 km). Within the data constraints, it is found that the variations in D properties are similar for the northern and southern hemispheres, and peak near southern summer solstice. Trends in the D Lyman‐α brightness, temperature, density, and escape rate are increasing during the beginning of the dust storm season, peak near southern summer solstice, and decrease toward the end of the dust storm season. This suggests that seasonal drivers at Mars cause deuterium in the upper Atmosphere to become globally enhanced when Mars is closest to the Sun and during the martian dust season when water is provided to the upper Atmosphere by subsurface, hydrological, and dust storm dynamics.
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ion densities in the nightside ionosphere of Mars effects of electron impact ionization
2017Co-Authors: Z Girazian, Richard Jonathan Lillis, M K Elrod, C M Fowler, P Mahaffy, Mehdi Benna, D.l. MitchellAbstract:We use observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to show how superthermal electron fluxes and crustal magnetic fields affect ion densities in the nightside ionosphere of Mars. We find that, due to electron impact ionization, high electron fluxes significantly increase the CO 2+, O+, and O 2+ densities below 200 km, but only modestly increase the NO+ density. High electron fluxes also produce distinct peaks in the CO 2+, O+, and O 2+ altitude profiles. We also find that superthermal electron fluxes are smaller near strong crustal magnetic fields. Consequently, nightside ion densities are also smaller near strong crustal fields because they decay without being replenished by electron impact ionization. Furthermore, the NO+/O 2+ ratio is enhanced near strong crustal fields because, in the absence of electron impact ionization, O 2+ is converted into NO+ and not replenished. Our results show that electron impact ionization is a significant source of CO 2+, O+, and O 2+ in the nightside ionosphere of Mars.
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unique non earthlike meteoritic ion behavior in upper Atmosphere of Mars
2017Co-Authors: J. M. Grebowsky, Mehdi Benna, P R Mahaffy, G Collinson, John M C Plane, Bruce M. JakoskyAbstract:Interplanetary dust particles have long been expected to produce permanent ionospheric metal ion layers at Mars, as on Earth, but the two environments are so different that uncertainty existed as to whether terrestrial-established understanding would apply to Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission made the first in situ detection of the continuous presence of Na+, Mg+, and Fe+ at Mars and indeed revealed non-Earthlike features/processes. There is no separation of the light Mg+ and the heavy Fe+ with increasing altitude as expected for gravity control. The metal ions are well-mixed with the neutral Atmosphere at altitudes where no mixing process is expected. Isolated metal ion layers mimicking Earth's sporadic E layers occur despite the lack of a strong magnetic field as required at Earth. Further, the metal ion distributions are coherent enough to always show atmospheric gravity wave signatures. All features and processes are unique to Mars.
J. I. Deighan - One of the best experts on this subject based on the ideXlab platform.
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carbon photochemical escape rates from the modern Mars Atmosphere
2021Co-Authors: R V Yelle, Robert Lillis, J. I. DeighanAbstract:Abstract We provide a comprehensive update of photochemical escape rates of atomic carbon from the present-day Martian Atmosphere using a one-dimensional photochemical model and a Monte Carlo escape model. The photochemical model incorporates new results relevant to carbon photochemistry at Mars, including new cross sections for photodissociation of CO 2 into C and O 2 (Lu et al. 2014) and electron impact dissociation of CO (Ajello et al. 2019). We find the newly included channel of CO 2 photodissociation to be the largest contributor to C escape, at 34%–58%. CO photodissociation and CO + dissociative recombination, which have been discussed extensively in the literature, also show up as significant sources of hot C atoms, with respective contributions of 15%–23% and 7%–10%. Electron impact dissociation of CO 2 (11%–15%) and photoionization of CO (6%–20%) are also important channels. Overall, escape rates vary over 3– 11 × 1 0 23 s−1, with an increase of 70% at perihelion compared to aphelion, and a much larger increase of 133% at solar maximum compared to solar minimum. While these present escape rates give a total integrated escape of only 1.3 mbar of CO 2 when multiplied by 3.6 billion years, the better characterization of carbon photochemistry and escape from this study will enable us to more reliably extrapolate backwards in time to when conditions of the Martian Atmosphere were significantly different from those of today.
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Martian mesospheric cloud observations by IUVS on MAVEN: Thermal tides coupled to the upper Atmosphere
2017Co-Authors: Michael H Stevens, J. I. Deighan, M. Crismani, Nicholas M. Schneider, Arnaud Stiepen, A. Ian F. Stewart, Sonal K. Jain, David E. Siskind, J. Scott Evans, Michael Scott ChaffinAbstract:We report observations of Martian mesospheric ice clouds and thermospheric scale heights by the Imaging Ultraviolet Spectrograph on NASA's Mars Atmosphere and Volatile Evolution mission. The clouds are observed between 6 AM and 8 AM local time using mid-UV limb observations between 60 and 80 km tangent altitude where ice particles that scatter sunlight can appear as detached layers near the equator. The equatorial longitudinal distribution shows populations of clouds near -110° E and -10° E as well as a population near 90° E, which does not have a clear precedent. The cloud populations indicate a wave 3 pattern near 70 km, which is confirmed by independent mesospheric temperature observations. Scale heights 100 km above the clouds derived from concurrent IUVS observations also reveal a wave 3 longitudinal structure, suggesting that the temperature oscillations enabling the formation of mesospheric clouds couple to the upper Atmosphere.
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MAVEN IUVS observations of the aftermath of the Comet Siding Spring meteor shower on Mars
2016Co-Authors: N. M. Schneider, A I F Stewart, Franck Montmessin, William E. Mcclintock, J. S. Evans, Roger V. Yelle, Jennifer M Plane, M. H. Stevens, J. I. Deighan, Michael S Chaffin, Gregory M. Holsclaw, J. T. Clarke, J. D. Carrillo-Sánchez, M. Crismani, A. Stiepen, S. K. Jain, Bruce M. JakoskyAbstract:We report the detection of intense emission from magnesium and iron in Mars' Atmosphere caused by a meteor shower following Comet Siding Spring's close encounter with Mars. The observations were made with the Imaging Ultraviolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile EvolutioN spacecraft orbiting Mars. Ionized magnesium caused the brightest emission from the planet's Atmosphere for many hours, resulting from resonant scattering of solar ultraviolet light. Modeling suggests a substantial fluence of low-density dust particles 1–100 µm in size, with the large amount and small size contrary to predictions. The event created a temporary planet-wide ionospheric layer below Mars' main dayside ionosphere. The dramatic meteor shower response at Mars is starkly different from the case at Earth, where a steady state metal layer is always observable but perturbations caused by even the strongest meteor showers are challenging to detect.
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The Imaging Ultraviolet Spectrograph (IUVS) for the MAVEN Mission
2015Co-Authors: William E. Mcclintock, Gregory M. Holsclaw, John T. Clarke, Alan C. Hoskins, Roger V. Yelle, Nicholas M. Schneider, Franck Montmessin, Ian Stewart, J. I. DeighanAbstract:The Imaging Ultraviolet Spectrograph (IUVS) is one of nine science instruments aboard the Mars Atmosphere and Volatile and EvolutioN (MAVEN) spacecraft. MAVEN, launched in November 18, 2013 and arriving at Mars in September 2014, is designed to explore the planet’s upper Atmosphere and ionosphere and examine their interaction with the solar wind and solar ultraviolet radiation. IUVS is one of the most powerful spectrographs sent to another planet, with several key capabilities: (1) separate Far-UV & Mid-UV channels for stray light control, (2) a high resolution echelle mode to resolve deuterium and hydrogen emission, (3) internal instrument pointing and scanning capabilities to allow complete mapping and nearly-continuous operation, and (4) optimization for airglow studies.
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retrieval of co2 and n2 in the martian thermosphere using dayglow observations by iuvs on maven
2015Co-Authors: J. S. Evans, J. I. Deighan, M. Crismani, A I F Stewart, M. S. Chaffin, Michael H Stevens, J D Lumpe, N Schneider, Sonal Jain, Arnaud StiepenAbstract:We present direct number density retrievals of carbon dioxide (CO2) and molecular nitrogen (N2) for the upper Atmosphere of Mars using limb scan observations during October and November 2014 by the Imaging Ultraviolet Spectrograph on board NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We use retrieved CO2 densities to derive temperature variability between 170 and 220 km. Analysis of the data shows (1) low-mid latitude northern hemisphere CO2 densities at 170 km vary by a factor of about 2.5, (2) on average, the N2/CO2 increases from 0.042 ± 0.017 at 130 km to 0.12 ± 0.06 at 200 km, and (3) the mean upper atmospheric temperature is 324 ± 22 K for local times near 14:00.
R V Yelle - One of the best experts on this subject based on the ideXlab platform.
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carbon photochemical escape rates from the modern Mars Atmosphere
2021Co-Authors: R V Yelle, Robert Lillis, J. I. DeighanAbstract:Abstract We provide a comprehensive update of photochemical escape rates of atomic carbon from the present-day Martian Atmosphere using a one-dimensional photochemical model and a Monte Carlo escape model. The photochemical model incorporates new results relevant to carbon photochemistry at Mars, including new cross sections for photodissociation of CO 2 into C and O 2 (Lu et al. 2014) and electron impact dissociation of CO (Ajello et al. 2019). We find the newly included channel of CO 2 photodissociation to be the largest contributor to C escape, at 34%–58%. CO photodissociation and CO + dissociative recombination, which have been discussed extensively in the literature, also show up as significant sources of hot C atoms, with respective contributions of 15%–23% and 7%–10%. Electron impact dissociation of CO 2 (11%–15%) and photoionization of CO (6%–20%) are also important channels. Overall, escape rates vary over 3– 11 × 1 0 23 s−1, with an increase of 70% at perihelion compared to aphelion, and a much larger increase of 133% at solar maximum compared to solar minimum. While these present escape rates give a total integrated escape of only 1.3 mbar of CO 2 when multiplied by 3.6 billion years, the better characterization of carbon photochemistry and escape from this study will enable us to more reliably extrapolate backwards in time to when conditions of the Martian Atmosphere were significantly different from those of today.
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evaluating local ionization balance in the nightside martian upper Atmosphere during maven deep dip campaigns
2019Co-Authors: S. Stone, Jun Cui, Yt Cao, R V Yelle, Erik Vigren, Niklas J T Edberg, Cl Shen, Yong WeiAbstract:Combining the Mars Atmosphere and Volatile Evolution (MAVEN) measurements of atmospheric neutral and ion densities, electron temperature, and energetic electron intensity, we perform the first quan ...
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Mars atmospheric history derived from upper Atmosphere measurements of 38ar 36ar
2017Co-Authors: Bruce M. Jakosky, M K Elrod, P Mahaffy, Mehdi Benna, S. Stone, R V Yelle, M Slipski, N AlsaeedAbstract:The history of Mars’ Atmosphere is important for understanding the geological evolution and potential habitability of the planet. We determine the amount of gas lost to space through time using measurements of the upper-atmospheric structure made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. We derive the structure of 38Ar/36Ar between the homopause and exobase altitudes. Fractionation of argon occurs as a result of loss of gas to space by pickup-ion sputtering, which preferentially removes the lighter atom. The measurements require that 66% of the atmospheric argon has been lost to space. Thus, a large fraction of Mars’ atmospheric gas has been lost to space, contributing to the transition in climate from an early, warm, wet environment to today’s cold, dry Atmosphere.
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probing the martian Atmosphere with maven iuvs stellar occultations
2015Co-Authors: H Groller, J. I. Deighan, A I F Stewart, Franck Montmessin, R V Yelle, N Schneider, Sonal Jain, Tommi Koskinen, G Lacombe, M. S. ChaffinAbstract:The first campaign of stellar occultations with the Imaging Ultraviolet Spectrograph (IUVS) instrument on board of Mars Atmosphere and Volatile EvolutioN (MAVEN) mission was executed between 24 and 26 March 2015. From this campaign 13 occultations are used to retrieve CO2 and O2 number densities in the altitude range between 100 and 150 km. Observations probe primarily the low-latitude regions on the nightside of the planet, just past the dawn and dusk terminator. Calculation of temperature from the CO2 density profiles reveals that the lower thermosphere is significantly cooler than predicted by the models in the Mars Climate Database. A systematically cold layer with temperatures of 105–120 K is seen in the occultations at a pressure level around 7 × 10−6 Pa.
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structure and composition of the neutral upper Atmosphere of Mars from the maven ngims investigation
2015Co-Authors: P R Mahaffy, M K Elrod, Mehdi Benna, S. Stone, S W Bougher, R V Yelle, Bruce M. JakoskyAbstract:The Mars Atmosphere and Volatile EvolutioN (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS) provides sensitive detections of neutral gas and ambient ion composition. NGIMS measurements of nine atomic and molecular neutral species, and their variation with altitude, latitude, and solar zenith angle are reported over several months of operation of the MAVEN mission. Sampling NGIMS signals from multiple neutral species every several seconds reveals persistent and unexpectedly large amplitude density structures. The scale height temperatures are mapped over the course of the first few months of the mission from high down to midlatitudes. NGIMS measurements near the homopause of 40Ar/N2 ratios agree with those reported by the Sample Analysis at Mars investigation and allow the altitude of the homopause for the most abundant gases to be established.
D.l. Mitchell - One of the best experts on this subject based on the ideXlab platform.
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ion densities in the nightside ionosphere of Mars effects of electron impact ionization
2017Co-Authors: Z Girazian, Richard Jonathan Lillis, M K Elrod, C M Fowler, P Mahaffy, Mehdi Benna, D.l. MitchellAbstract:We use observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to show how superthermal electron fluxes and crustal magnetic fields affect ion densities in the nightside ionosphere of Mars. We find that, due to electron impact ionization, high electron fluxes significantly increase the CO 2+, O+, and O 2+ densities below 200 km, but only modestly increase the NO+ density. High electron fluxes also produce distinct peaks in the CO 2+, O+, and O 2+ altitude profiles. We also find that superthermal electron fluxes are smaller near strong crustal magnetic fields. Consequently, nightside ion densities are also smaller near strong crustal fields because they decay without being replenished by electron impact ionization. Furthermore, the NO+/O 2+ ratio is enhanced near strong crustal fields because, in the absence of electron impact ionization, O 2+ is converted into NO+ and not replenished. Our results show that electron impact ionization is a significant source of CO 2+, O+, and O 2+ in the nightside ionosphere of Mars.
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comparative study of the martian suprathermal electron depletions based on Mars global surveyor Mars express and Mars Atmosphere and volatile evolution mission observations
2017Co-Authors: D.l. Mitchell, Morgane Steckiewicz, P Garnier, N Andre, L Andersson, E PenouAbstract:Nightside suprathermal electron depletions have been observed at Mars by three spacecraft to date: Mars Global Surveyor (MGS), Mars EXpress (MEX) and the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. This spatial and temporal diversity of measurements allows us to propose here a comprehensive view of the Martian electron depletions through the first multi-spacecraft study of the phenomenon. We have analyzed data recorded by the three spacecraft from 1999 to 2015 in order to better understand the distribution of the electron depletions and their creation mechanisms. Three simple criteria adapted to each mission have been implemented to identify more than 134 500 electron depletions observed between 125 and 900 km altitude. The geographical distribution maps of the electron depletions detected by the three spacecraft confirm the strong link existing between electron depletions and crustal magnetic field at altitudes greater than ~170 km. At these altitudes, the distribution of electron depletions is strongly different in the two hemispheres, with a far greater chance to observe an electron depletion in the Southern hemisphere, where the strongest crustal magnetic sources are located. However, the unique MAVEN observations reveal that below a transition region near 160-170 km altitude the distribution of electron depletions is the same in both hemispheres, with no particular dependence on crustal magnetic fields. This result supports the suggestion made by previous studies that these low altitudes events are produced through electron absorption by atmosphericCO2.
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Comparative study of the Martian suprathermal electron depletions based on Mars Global Surveyor, Mars Express and Mars Atmosphere and Volatile EvolutioN missions observations
2016Co-Authors: Steckiewicz M, D.l. Mitchell, Garnier P, André N, Andersson L, Penou E, Beth A, Fedorov A, Sauvaud J-a, Mazelle CAbstract:Nightside suprathermal electron depletions have been observed at Mars by three spacecraft to date: Mars Global Surveyor, Mars Express, and the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. This spatial and temporal diversity of measurements allows us to propose here a comprehensive view of the Martian electron depletions through the first multispacecraft study of the phenomenon. We have analyzed data recorded by the three spacecraft from 1999 to 2015 in order to better understand the distribution of the electron depletions and their creation mechanisms. Three simple criteria adapted to each mission have been implemented to identify more than 134,500 electron depletions observed between 125 and 900 km altitude. The geographical distribution maps of the electron depletions detected by the three spacecraft confirm the strong link existing between electron depletions and crustal magnetic field at altitudes greater than ~170 km. At these altitudes, the distribution of electron depletions is strongly different in the two hemispheres, with a far greater chance to observe an electron depletion in the Southern Hemisphere, where the strongest crustal magnetic sources are located. However, the unique MAVEN observations reveal that below a transition region near 160–170 km altitude the distribution of electron depletions is the same in both hemispheres, with no particular dependence on crustal magnetic fields. This result supports the suggestion made by previous studies that these low-altitudes events are produced through electron absorption by atmospheric CO2
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first results of the maven magnetic field investigation
2015Co-Authors: J E P Connerney, D.l. Mitchell, J S Halekas, Jared Espley, C Mazelle, G A Dibraccio, Jacob Gruesbeck, R J OliversenAbstract:Two Mars Atmosphere and Volatile EvolutioN magnetic field sensors sample the ambient magnetic field at the outer edge of each solar array. We characterized relatively minor spacecraft-generated magnetic fields using in-flight subsystem tests and spacecraft maneuvers. Dynamic spacecraft fields associated with the power subsystem (≤1 nT) are compensated for using spacecraft engineering telemetry to identify active solar array circuits and monitor their electrical current production. Static spacecraft magnetic fields are monitored using spacecraft roll maneuvers. Accuracy of measurement of the environmental magnetic field is demonstrated by comparison with field directions deduced from the symmetry properties of the electron distribution function measured by the Solar Wind Electron Analyzer. We map the bow shock, magnetic pileup boundary, the V × B convection electric field and ubiquitous proton cyclotron, and 1 Hz waves in the ion foreshock region.
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maven observations of solar wind hydrogen deposition in the Atmosphere of Mars
2015Co-Authors: J S Halekas, D.l. Mitchell, Mehdi Benna, Jared Espley, C Mazelle, P R Mahaffy, J E P Connerney, R J Lillis, T E CravensAbstract: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.