Measurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field ...(IMF) BY. We find that the magnetotail lobes exhibit a ~45deg twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross-tail current sheet is rotated away from the expected location for a Venus-like induced magnetotail based on nominal IMF draping. Data-model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth.
The interaction between Mars and the solar wind results in different plasma regimes separated by several boundaries, among which the separation between the sheath flow and the ionosphere is ...complicated. Previous studies have provided different and sometimes opposite findings regarding this region. In this study, we utilize observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission to revisit boundaries within this region and perhaps reconcile some differences. More specifically, we start with the photoelectron boundary (PEB), a topological boundary that separates magnetic field lines having access to the dayside ionosphere (open or closed) from those connected to the solar wind on both ends (draped). We find that large gradients in the planetary ion densiti occur across the PEB and that the dominant ion switches from heavy planetary ions to protons near the PEB, indicating that the PEB falls within the ion composition boundary (ICB). Furthermore, our results show that the PEB is not a pressure balance boundary; rather the magnetic pressure dominates both sides of the PEB. Meanwhile, we find that the PEB is located where the shocked solar wind flow stops penetrating deeper into the ionosphere. These findings suggest the PEB marks the top of the Mars dayside ionosphere and also the interface where the sheath plasma flow deflects around the obstacle going downstream.
Key Points
Large gradients in planetary ion density occur across the photoelectron boundary (PEB) and the PEB falls within the ion composition boundary
The PEB can be considered as the top of the Mars dayside ionosphere
The PEB is not a pressure balance boundary but is located where the shocked sheath flow is diverted around the ionosphere
The Martian magnetotail exhibits a highly twisted configuration, shifting in response to changes in polarity of the interplanetary magnetic field's (IMF) dawn‐dusk (BY) component. Here, we analyze ...∼6000 MAVEN orbits to quantify the degree of magnetotail twisting (θTwist) and assess variations as a function of (a) strong planetary crustal field location, (b) Mars season, and (c) downtail distance. The results demonstrate that θTwist is larger for a duskward (+BY) IMF orientation a majority of the time. This preference is likely due to the local orientation of crustal magnetic fields across the surface of Mars, where a +BY IMF orientation presents ideal conditions for magnetic reconnection to occur. Additionally, we observe an increase in θTwist with downtail distance, similar to Earth's magnetotail. These findings suggest that coupling between the IMF and moderate‐to‐weak crustal field regions may play a major role in determining the magnetospheric structure at Mars.
Plain Language Summary
MAVEN magnetic field data are analyzed to understand factors that may influence the magnetotail structure at Mars. The Martian magnetotail lobes are observed to be twisted and the degree of this twist can vary. In this work, we calculate the degree of tail twist and monitor how it changes. To understand how the twist changes, we examine these variations as a function of Mars crustal field location, Mars season, and downtail distance away from Mars.
Key Points
Mars' magnetotail can be twisted up to 60 deg away from its expected location based on interplanetary magnetic field (IMF) draping, much greater than Earth's tail twist
MAVEN observations show that Mars' tail exhibits larger twisting for +BY IMF orientation, compared to −BY IMF
Mars crustal magnetic fields may play a significant role in shaping the twisted structure of the Martian magnetotail
Many aspects of the Sun‐Mars interaction have been investigated during solar transient events with measurements from multiple spacecrafts and also simulation efforts. Limited discussion has been paid ...to magnetic topology response to disturbed upstream conditions. The implications of topology changes include, but are not limited to, the pattern of energetic particle precipitation into the Martian atmosphere and the impact on cold ion escape during solar transient events as low‐energy ion escape is dependent on magnetic topology. In this study, we investigate the magnetic topology response to the 2017 September interplanetary coronal mass ejection (ICME) event with measurements collected by the Mars Atmospheric and Volatile EvolutioN spacecraft. It is found that the interface between draped interplanetary magnetic field and closed field lines was moved from 800–1400 km in altitude during quiet conditions to 200–400 km after ICME arrived at Mars and then relaxed back to high altitudes again after the event. To gain insight into magnetic topology response on a global scale, we first validate magnetic topology from a time‐dependent simulation with a single‐fluid multispecies magnetohydrodynamic (MHD) model by comparing magnetic topology determined from Mars Atmospheric and Volatile EvolutioN data, which shows a good agreement. Then we present MHD predictions of global magnetic topology changes during this ICME event. In addition to a deeper interplanetary magnetic field penetration, MHD results suggest more open field lines in response to the ICME event.
Plain Language Summary
An important way for Mars to lose its atmosphere over time is through solar wind striping away ions from Mars. The planet lacks of an intrinsic global magnetic field but possesses localized crustal fields so that solar wind and the interplanetary magnetic field have direct access to the Martian ionosphere. This effect is intensified when a coronal mass ejection is emitted from the Sun and hits Mars. Charged particles subject to electromagnetic forces so that the magnetic topology, whether a magnetic field line connects to Mars and/or solar wind, is an important aspect of the Sun‐Mars interaction and also closely related to energy and particle transport at Mars and low‐energy ion escape. In this study, we investigate how the Martian magnetic topology responds to the coronal mass ejection event occurred in September 2017 with measurements from the Mars Atmosphere Volatile and Evolution spacecraft and also simulation results from a magnetohydrodynamic model. It is found that during the event, interplanetary magnetic field penetrates deeper into the atmosphere and also there are more magnetic field lines connecting Mars and solar wind, which means ions subject to escape starting from lower altitudes, where ion densities are higher.
Key Points
From MAVEN data, IMF is found to penetrate deeper over the northern hemisphere due to enhanced solar wind dynamic pressure during the ICME
Topology from MHD shows a good agreement with data and provides insights into a global response
MHD results suggest deeper IMF penetration and more open field lines during the ICME event
Abstract Venus, lacking an intrinsic global dipole magnetic field, serves as a textbook example of an induced magnetosphere, formed by interplanetary magnetic fields (IMF) enveloping the planet. Yet, ...various aspects of its magnetospheric dynamics and planetary ion outflows are complex and not well understood. Here we analyze plasma and magnetic field data acquired during the fourth Venus flyby of the Parker Solar Probe (PSP) mission and show evidence for closed topology in the nightside and downstream portion of the Venus magnetosphere (i.e., the magnetotail). The formation of the closed topology involves magnetic reconnection—a process rarely observed at non-magnetized planets. In addition, our study provides an evidence linking the cold Venusian ion flow in the magnetotail directly to magnetic connectivity to the ionosphere, akin to observations at Mars. These findings not only help the understanding of the complex ion flow patterns at Venus but also suggest that magnetic topology is one piece of key information for resolving ion escape mechanisms and thus the atmospheric evolution across various planetary environments and exoplanets.
Abstract
Mars’s magnetosphere is hybrid, having contributions from both an induced magnetosphere like Venus and the localized crustal magnetic fields. However, the planetary fields also include ...large-scale, more global components. In this study, we investigate their role in Mars’s magnetospheric topological responses to the interplanetary magnetic field (IMF) clock angle using observations from the Mars Atmospheric Volatile and EvolutioN mission. We show that the large-scale planetary field has a “dipole-like” influence on the Mars global magnetosphere by examining the open field topology. We find that the “dipole-like” planetary field, as at Earth, results in a more open magnetosphere during southward IMF. The clock angle effects on the twisted magnetotail current sheet are similarly consistent with this analogy. It reinforces the idea that Mars’s magnetosphere and solar wind interaction are more Earth-like than previously thought.
Dust storms and the atmospheric waves can play a significant role in the dynamics in the upper neutral atmosphere of Mars. Recent observations found that a periodic variation of neutral H and O ...exists in the upper atmosphere, which is likely associated with atmospheric waves that occurred during the regional dust storm on 4 September 2016. However, such periodic variations accompanying the dust storm are far from understood in terms of the Martian ionized particles (i.e., ionosphere). Here we investigated the periodic variation of the ion density in the Martian ionosphere during the regional dust storm in September 2016 based on the MAVEN/STATIC observations. Assuming a simple Chapman layer model, we implemented numerical fitting for the ion density altitude profile to retrieve the peak ion densities in the Martian ionosphere. We then applied periodogram analysis to these peak ion densities in order to identify the peak periodicities together with their confidence levels. We identified several distinct peak periodicities with a scale from ∼1 day up to ∼20 days. The peak periodicities around 6–9 days are comparable to those seen in the Martian neutral atmosphere. In addition, the other peak periodicities likely correspond to the periodic crossings of the local crustal fields and periodic variation of the upstream solar wind, indicating a strong regional coupling between the lower atmosphere and the upstream solar wind.
Key Points
We investigated periodic variations in the Martian dayside ionosphere during the regional dust storm
We found several distinct peak periodicities in the Martian dayside ionosphere with a scale from ∼1 day up to several weeks
Periodic variation (6–9 days) in the Martian dayside ionosphere is likely comparable to those previously identified in the neutral H and O
Ion acceleration in Mars’ twisted magnetotail Curry, Shannon M; Tatum, P; Mitchell, D ...
Monthly notices of the Royal Astronomical Society. Letters,
11/2022, Letnik:
517, Številka:
1
Journal Article
Recenzirano
ABSTRACT
Mars lacks a global magnetic field and instead has a unique, ‘hybrid’ magnetosphere composed of crustal magnetic fields, which are stronger in the Southern hemisphere than the Northern ...hemisphere. These crustal fields are believed to drive a twist in the magnetotail at Mars. This is important because heavy ions escape from this induced magnetotail, which is a major source of atmospheric erosion. We present analysis of heavy ions produced in Mars’ upper atmosphere that are transported downtail along the twisted current sheet and observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We identified O+, O$_2\, ^+$, and CO$_2\, ^+$ being accelerated to different energies at a range of distances downtail and found that heavy ions in the 10–50 eV energy population have the highest flux. We present tail slices of ion fluxes for different interplanetary magnetic field (IMF) configurations based on the BY component of the IMF and find that the different configurations affect the degree of tail twist and the transport of heavy ions in the induced magnetotail lobes. We find that the total escape rate for O+, O$_2\, ^+$, and CO$_2\, ^+$ is 5.5e24 s-1, with 50% escaping between 2–200 eV.
Without the shielding of a substantial intrinsic dipole magnetic field, the atmospheres of Mars and Venus are particularly susceptible to similar atmospheric ion energization and scavenging ...processes. However, each planet has different attributes and external conditions controlling its high altitude planetary ion spatial and energy distributions. This paper describes analogous test particle simulations in background MHD fields that allow us to compare the properties and fates, precipitation or escape, of the mainly O+ atmospheric pick-up ions at Mars and Venus. The goal is to illustrate how atmospheric and planetary scales affect the upper atmospheres and space environments of our terrestrial planet neighbors. The results show the expected convection electric field-related hemispheric asymmetries in both precipitation and escape, where the degree of asymmetry at each planet is determined by the planetary scale and local interplanetary field strength. At Venus, the kinetic treatment of O+ reveals a strong nightside source of precipitation while Mars' crustal fields complicate the simple asymmetry in ion precipitation and drive a dayside source of precipitation. The pickup O+ escape pattern at both Venus and Mars exhibits low energy tailward escape, but Mars exhibits a prominent, high energy ‘polar plume’ feature in the hemisphere of the upward convection electric field while the Venus ion wake shows only a modest poleward concentration. The overall escape is larger at Venus than Mars (2.1×1025 and 4.3×1024 at solar maximum, respectively), but the efficiency (likelihood) of O+ escaping is 2–3 times higher at Mars. The consequences of these comparisons for pickup ion related atmospheric energy deposition, loss rates, and detection on spacecraft including PVO, VEX, MEX and MAVEN are considered. In particular, both O+ precipitation and escape show electric field controlled asymmetries that grow with energy, while the O+ fluxes and energy spectra at selected spatial locations show characteristic signatures of the pickup related acceleration and precipitation.
•Heavy ion precipitation is controlled by the E-field at Venus and Mars.•The solar wind is more efficient at removing O+ via pickup at Mars than Venus.•Mars and Venus have tailward O+ escape but Mars has a stronger polar plume.•Kinetic effects are more important at Mars than Venus.
Superthermal electron precipitation is one of the main sources supporting the Mars nightside ionosphere. It is expected that solar wind electron fluxes are to increase significantly during ...interplanetary coronal mass ejections (ICMEs) and therefore an enhanced nightside ionospheric density. This study is to quantify the variation of the precipitating and deposited electron fluxes during five extreme ICMEs encountered by Mars Global Surveyor (MGS). We find that energy fluxes correlate better with the upstream dynamic pressure proxy than number fluxes and electron fluxes increase more at high energies, which means that electrons tend to have a lower peak production altitude during storm times. The precipitating and net/deposited fluxes are increased up to an order of magnitude from low to high dynamic pressures. The estimated total electron content (TEC) is a few times of 1014 m−2 for quiet times and on the order of 1015 m−2 for storm times, with an enhancement up to an order of magnitude locally near strong crustal fields. Crustal magnetic fields have an effect on the deposited fluxes with more prominent magnetic reflection over strong magnetic fields during quiet periods, which is significantly reduced during storm times. Lastly, we estimate a global energy input from downward fluxes of 1.1 × 108 and 5.5 × 108 W and the globally deposited energy from net fluxes of 2.0 × 107 and 1.6 × 108 W for quiet and storm time periods, a factor of 5 and 8 enhancement globally, respectively, but up to an order of magnitude locally near strong crustal fields.
Key Points
We quantify the variation of nightside precipitating and deposited electron fluxes during five extreme ICME events encountered by MGS
The estimated TEC is on the order of 1014 m−2 for quiet periods and 1015 m−2 for storm periods because of enhanced electron precipitation
Crustal magnetic fields reduce deposited fluxes during quiet time because of magnetic reflection, which is largely reduced during storm time
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