Mars nightside electrons over strong crustal fields

Shane, A. D.; Xu, Shaosui; Liemohn, Michael W.; Mitchell, David

doi:10.1002/2015ja021947

Cited by 30 publications

(49 citation statements)

References 51 publications

(111 reference statements)

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“…Electron depletions are large reductions in superthermal electron flux on the nightside of Mars that were first observed by MGS and have since been investigated by several authors (Dubinin et al, ; Lillis & Brain, ; Mitchell et al, ; Steckiewicz et al, ; Shane et al, ). These depletions are due to the presence of closed loops of magnetic field that have lost their associated electron population through recombination with the atmosphere.…”

Section: Interpretation Of Pitch Angle Distributionsmentioning

confidence: 99%

Characterization of Low‐Altitude Nightside Martian Magnetic Topology Using Electron Pitch Angle Distributions

et al. 2017

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Magnetic field lines at Mars act as direct pathways for both energy inflow and ion escape. Local variations in magnetic field topology can therefore directly impact the interaction between the solar wind and the Martian ionosphere. One method of analyzing magnetic topology is through the use of electron pitch angle distributions (PADs). Previous PAD investigations have characterized magnetic topology in the Martian system using data from the Mars Global Surveyor spacecraft, but these studies were orbitally constrained to ∼400 km altitude and 2 a.m./2 p.m. local time. With the Mars Atmosphere and Volatile Evolution (MAVEN) mission, we are now able to extend this analysis to a larger range of altitudes and local times. Here we use electron PADs measured using the Solar Wind Electrostatic Analyzer and Magnetometer instruments on MAVEN to analyze the magnetic topology of the nightside Martian environment. We use several characteristic PAD shapes to determine where Martian magnetic field lines are open or closed to the solar wind and present frequency maps of how these PAD shapes vary both geographically and with altitude. Finally, we present an initial analysis of the variation of the PAD shapes with local time, finding that trapped electron distributions become increasingly frequent as crustal fields rotate from dusk to dawn across the nightside of Mars.

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Section: Interpretation Of Pitch Angle Distributionsmentioning

confidence: 99%

Characterization of Low‐Altitude Nightside Martian Magnetic Topology Using Electron Pitch Angle Distributions

et al. 2017

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“…Shane et al (2016) for example used an arbitrary base altitude of 90 km instead of the surface of Mars, assuming that the light is attenuated by the atmosphere below this altitude, in order to quantify the deposition of photoelectron and solar wind electron populations on the nightside of Mars. The terminator is the boundary between the region where photons are received and the region where they are not.…”

Section: Definition Of the Uv Terminatormentioning

confidence: 99%

Dawn/Dusk Asymmetry of the Martian UltraViolet Terminator Observed Through Suprathermal Electron Depletions

et al. 2019

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Suprathermal electron depletions are structures of the nightside ionosphere of Mars resulting from an equilibrium between electron loss and creation processes. Photoionization of oxygen and carbon dioxide by UV and EUV photons is the main ionization process of the Martian atmosphere. The observation of suprathermal electron depletions is strongly unexpected in the portion of the Martian environment where photoionization can occur. This region is delimited by the UltraViolet (UV) terminator, behind which no UV ionizing photons are detected. In this study suprathermal electron depletions are used to determine the position of the UV terminator thanks to MAVEN observations. The MAVEN spacecraft is now in its fourth year of data recording and has already covered more than one Martian year, a large range of latitude, local time, and solar zenith angle in the nightside down to 110‐km altitude. This coverage enables us to determine the approximate position of the UV terminator over one Martian year. We then investigate the variation of its position on the dawnside and duskside and depending on seasons. Our results are compared with models of the Martian atmosphere and in situ data of the atmospheric composition which all highlight an asymmetry between the duskside and the dawnside at equinox. However, models show an inversion in the position of the dusk and the dawn UV terminator at perihelion and aphelion, which cannot yet be confirmed or disproved by the data.

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“…Open field lines, with one end intersecting the collisional atmosphere and the other end connected to the solar wind, permit particle/energy exchange between the Martian ionosphere and the solar wind. Energetic electron precipitation [e.g., Lillis and Brain , ; Xu et al ., ; Shane et al ., ] through open fields can cause ionization [e.g., Lillis et al ., ; Fillingim et al ., ; Fillingim et al ., ], heating [e.g., Krymskii et al ., , ], and excitation (probably aurora [e.g., Bertaux et al ., ; Brain et al ., ; Liemohn et al ., ; Leblanc et al ., ; Shane et al ., ]). Open magnetic field lines attached to the dayside ionosphere also provide possible passages for ion escape [e.g., Lillis et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Martian low‐altitude magnetic topology deduced from MAVEN/SWEA observations

et al. 2017

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The Mars Atmosphere and Volatile Evolution mission has obtained comprehensive particle and magnetic field measurements. The Solar Wind Electron Analyzer provides electron energy‐pitch angle distributions along the spacecraft trajectory that can be used to infer magnetic topology. This study presents pitch angle‐resolved electron energy shape parameters that can distinguish photoelectrons from solar wind electrons, which we use to deduce the Martian magnetic topology and connectivity to the dayside ionosphere. Magnetic topology in the Mars environment is mapped in three dimensions for the first time. At low altitudes (<400 km) in sunlight, the northern hemisphere is found to be dominated by closed field lines (both ends intersecting the collisional atmosphere), with more day‐night connections through cross‐terminator closed field lines than in the south. Although draped field lines with ~100 km amplitude vertical fluctuations that intersect the electron exobase (~160–220 km) in two locations could appear to be closed at the spacecraft, a more likely explanation is provided by crustal magnetic fields, which naturally have the required geometry. Around 30% of the time, we observe open field lines from 200 to 400 km, which implies three distinct topological layers over the northern hemisphere: closed field lines below 200 km, open field lines with foot points at lower latitudes that pass over the northern hemisphere from 200 to 400 km, and draped interplanetary magnetic field above 400 km. This study also identifies open field lines with one end attached to the dayside ionosphere and the other end connected with the solar wind, providing a path for ion outflow.

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Mars nightside electrons over strong crustal fields

Cited by 30 publications

References 51 publications

Characterization of Low‐Altitude Nightside Martian Magnetic Topology Using Electron Pitch Angle Distributions

Characterization of Low‐Altitude Nightside Martian Magnetic Topology Using Electron Pitch Angle Distributions

Dawn/Dusk Asymmetry of the Martian UltraViolet Terminator Observed Through Suprathermal Electron Depletions

Martian low‐altitude magnetic topology deduced from MAVEN/SWEA observations

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