The Structure of Martian Magnetosphere at the Dayside Terminator Region as Observed on MAVEN Spacecraft

We analyzed 44 passes of the MAVEN spacecraft through the magnetosphere, arranged by the angle between electric field vector and the projection of spacecraft position radius vector in the YZ plane in MSE coordinate system (${\theta}$ E ). All passes were divided into 3 angular sectors near 0{\deg}, 90{\deg} and 180{\deg} ${\theta}$ E angles in order to estimate the role of IMF direction in plasma and magnetic properties of dayside Martian magnetosphere. The time interval chosen was from January 17 through February 4, 2016 when MAVEN was crossing the dayside magnetosphere at SZA ~ 70{\deg}. Magnetosphere as the region with prevailing energetic planetary ions is always found between the magnetosheath and the ionosphere. 3 angular sectors of dayside interaction region in MSE coordinate system with different orientation of the solar wind electric field vector E = -1/c V x B showed that for each sector one can find specific profiles of the magnetosheath, the magnetic barrier and the magnetosphere. Plume ions originate in the northern MSE sector where motion electric field is directed from the planet. This electric field ejects magnetospheric ions leading to dilution of magnetospheric heavy ions population, and this effect is seen in some magnetospheric profiles. Magnetic barrier forms in front of the magnetosphere, and relative magnetic field magnitudes in these two domains vary. The average height of the boundary with ionosphere is ~530 km and the average height of the magnetopause is ~730 km. We discuss the implications of the observed magnetosphere structure to the planetary ions loss mechanism.Comment: 24 pages, 13 figure

Upstream Ultra‐Low Frequency Waves Observed by MESSENGER’s Magnetometer: Implications for Particle Acceleration at Mercury’s Bow Shock

We perform the first statistical analysis of the main properties of waves observed in the 0.05–0.41 Hz frequency range in the Hermean foreshock by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Magnetometer. Although we find similar polarization properties to the “30 s” waves observed at the Earth’s foreshock, the normalized wave amplitude (δB/|B0|∼0.2) and occurrence rate (∼0.5%) are much smaller. This could be associated with relatively lower backstreaming proton fluxes, the smaller foreshock size and/or less stable solar wind (SW) conditions around Mercury. Furthermore, we estimate that the speed of resonant backstreaming protons in the SW reference frame (likely source for these waves) ranges between 0.95 and 2.6 times the SW speed. The closeness between this range and what is observed at other planetary foreshocks suggests that similar acceleration processes are responsible for this energetic population and might be present in the shocks of exoplanets.Key PointsWe perform the first statistical analysis (4,536 events) of the main properties of the lowest‐frequency waves in the Hermean foreshockSmall normalized wave amplitude (0.2) and occurrence (0.5%) are likely due to low backstreaming proton flux and variable external conditionsThe normalized backstreaming protons speed (∼0.95–2.6) suggests similar acceleration processes occur at several planetary shocksPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155492/1/grl60476.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155492/2/grl60476_am.pd

MESSENGER Observations of Mercury’s Nightside Magnetosphere Under Extreme Solar Wind Conditions: Reconnectionâ Generated Structures and Steady Convection

Mercury’s nightside magnetosphere is investigated under the impact of a coronal mass ejection (CME) and a highâ speed stream (HSS) with MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) observations. The CME was shown to produce a low plasma β (ratio of thermal pressure to magnetic pressure) magnetosheath, while the HSS creates a higher β magnetosheath. Reconnection at the dayside magnetopause was found to be stronger during the CME than the HSS, but both were stronger than the average condition (Slavin et al., 2014, https://doi.org/10.1002/2014JA020319). Here we show that the CME and HSS events produced large numbers of flux ropes and dipolarization fronts in the plasma sheet. The occurrence rates for the structures were approximately 2 orders of magnitude higher than under average conditions with the rates during CME’s being twice that of HSS’s. The flux ropes appeared as quasiperiodic flux rope groups. Each group lasted approximately 1 min and had a few large flux ropes followed by several smaller flux ropes. The lobe magnetic flux accounted for around half of the Mercury’s available magnetic flux with the flux during CME’s being larger than that of HSS’s. The CME produced a more dynamic nightside magnetosphere than the HSS. Further, for the CME event, the tail magnetic reconnection produced a distorted Hall magnetic field pattern and the Xâ line had a dawnâ dusk extent of 20% of the tail width. No magnetic flux loading and unloading events were observed suggesting that, during these intense driving conditions, Mercury’s magnetosphere responded with a type of quasiâ steady convection as opposed to the tail flux loadingâ unloading events seen at Earth.Key PointsCoronal mass ejections drive more intense nightside reconnection than high speed streamsUnder extreme conditions, magnetic reconnection produces a distorted Hall magnetic field pattern in the plasma sheetContinued intense solar wind forcing does not produce substorm magnetic flux loading and unloading of tail lobe instead steady convectionPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154381/1/jgra55534_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154381/2/jgra55534.pd

Magnetic Field Draping in Induced Magnetospheres: Evidence from the MAVEN Mission to Mars

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has been orbiting Mars since 2014 and now has over 10,000 orbits which we use to characterize Mars' dynamic space environment. Through global field line tracing with MAVEN magnetic field data we find an altitude dependent draping morphology that differs from expectations of induced magnetospheres in the vertical ($\hat Z$ Mars Sun-state, MSO) direction. We quantify this difference from the classical picture of induced magnetospheres with a Bayesian multiple linear regression model to predict the draped field as a function of the upstream interplanetary magnetic field (IMF), remanent crustal fields, and a previously underestimated induced effect. From our model we conclude that unexpected twists in high altitude dayside draping ($>$800 km) are a result of the IMF component in the $\pm \hat X$ MSO direction. We propose that this is a natural outcome of current theories of induced magnetospheres but has been underestimated due to approximations of the IMF as solely $\pm \hat Y$ directed. We additionally estimate that distortions in low altitude ($<$800 km) dayside draping along $\hat Z$ are directly related to remanent crustal fields. We show dayside draping traces down tail and previously reported inner magnetotail twists are likely caused by the crustal field of Mars, while the outer tail morphology is governed by an induced response to the IMF direction. We conclude with an updated understanding of induced magnetospheres which details dayside draping for multiple directions of the incoming IMF and discuss the repercussions of this draping for magnetotail morphology.Comment: Accepted in Journal of Geophysical Research: Space Physic

Achievements and Challenges in the Science of Space Weather

In June 2016 a group of 40 space weather scientists attended the workshop on Scientific Foundations of Space Weather at the International Space Science Institute in Bern. In this lead article to the volume based on the talks and discussions during the workshop we review some of main past achievements in the field and outline some of the challenges that the science of space weather is facing today and in the future.Peer reviewe

The Case for a New Frontiers-Class Uranus Orbiter: System Science at an Underexplored and Unique World with a Mid-scale Mission

Current knowledge of the Uranian system is limited to observations from the flyby of Voyager 2 and limited remote observations. However, Uranus remains a highly compelling scientific target due to the unique properties of many aspects of the planet itself and its system. Future exploration of Uranus must focus on cross-disciplinary science that spans the range of research areas from the planet's interior, atmosphere, and magnetosphere to the its rings and satellites, as well as the interactions between them. Detailed study of Uranus by an orbiter is crucial not only for valuable insights into the formation and evolution of our solar system but also for providing ground truths for the understanding of exoplanets. As such, exploration of Uranus will not only enhance our understanding of the ice giant planets themselves but also extend to planetary dynamics throughout our solar system and beyond. The timeliness of exploring Uranus is great, as the community hopes to return in time to image unseen portions of the satellites and magnetospheric configurations. This urgency motivates evaluation of what science can be achieved with a lower-cost, potentially faster-turnaround mission, such as a New Frontiers–class orbiter mission. This paper outlines the scientific case for and the technological and design considerations that must be addressed by future studies to enable a New Frontiers–class Uranus orbiter with balanced cross-disciplinary science objectives. In particular, studies that trade scientific scope and instrumentation and operational capabilities against simpler and cheaper options must be fundamental to the mission formulation

The case for a New Frontiers-class Uranus Orbiter:System science at an underexplored and unique world with a mid-scale mission

Current knowledge of the Uranian system is limited to observations from the flyby of Voyager 2 and limited remote observations. However, Uranus remains a highly compelling scientific target due to the unique properties of many aspects of the planet itself and its system. Future exploration of Uranus must focus on cross-disciplinary science that spans the range of research areas from the planet's interior, atmosphere, and magnetosphere to the its rings and satellites, as well as the interactions between them. Detailed study of Uranus by an orbiter is crucial not only for valuable insights into the formation and evolution of our solar system but also for providing ground truths for the understanding of exoplanets. As such, exploration of Uranus will not only enhance our understanding of the ice giant planets themselves but also extend to planetary dynamics throughout our solar system and beyond. The timeliness of exploring Uranus is great, as the community hopes to return in time to image unseen portions of the satellites and magnetospheric configurations. This urgency motivates evaluation of what science can be achieved with a lower-cost, potentially faster-turnaround mission, such as a New Frontiers–class orbiter mission. This paper outlines the scientific case for and the technological and design considerations that must be addressed by future studies to enable a New Frontiers–class Uranus orbiter with balanced cross-disciplinary science objectives. In particular, studies that trade scientific scope and instrumentation and operational capabilities against simpler and cheaper options must be fundamental to the mission formulation

The Search for Magnetotail Twisting at Mercury: Comparing MESSENGER Observations With the Terrestrial Case

Previous studies reported that the terrestrial and Martian magnetotails can become twisted due to the solar wind-planetary interaction; however, the associated physical processes proper of intrinsic and induced magnetospheres are still under debate. In particular, there is evidence that the Interplanetary Magnetic Field (IMF) dawn-dusk component (By) plays a major role in both environments, affecting the sense of twist. Here, we analyze all MErcury, Surface, Space ENvironment, GEochemistry and Ranging Magnetometer observations to investigate the IMF By influence on Mercury’s magnetotail. We find that Mercury’s tail twist is very small (≲3°), for a median downtail distance of ∼2 Mercury radii. We also identify a correlation between the IMF By and the local By component around the magnetotail current sheet. These results suggest the small (or lack of) twist may be explained by the dipolar field strength in the near-magnetotail. We examine this hypothesis by putting these observations into context with studies on the terrestrial magnetotail.Plain Language SummaryPrevious studies identified a twist in the magnetotail structures on Earth and Mars. This twist is affected by the dawn-dusk component (By) of the background magnetic field convected by the solar wind. To improve the current understanding of these phenomena, we analyze all MErcury, Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) magnetic field data in Mercury’s magnetotail. We find an upper bound for the tail twist of ∼3°, based on observations obtained centered at ∼2 Mercury radii downstream from the planet. Our results suggest the small (or lack of) twist at Mercury could be understood in terms of the dipolar field strength in the magnetotail region near the planet. We put these observations into context with conclusions reported at the terrestrial magnetotail and argue the Bepi-Colombo mission may see a more developed twist, as the planned apoapsis is expected to be further downtail from Mercury, compared to MESSENGER.Key PointsWe find an upper bound for Mercury’s near tail twist of ∼3°, in association with the Interplanetary Magnetic Field (IMF) dawn-dusk (By) componentThe IMF By is able to affect Mercury’s magnetotail current sheet and the local dipolar field can partly explain the small twistComparisons with observations from Earth suggest the tail twist could be detectable by Bepi-Colombo further downstream of MercuryPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/175475/1/grl65221.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/175475/2/grl65221_am.pd

MAVEN Survey of Magnetic Flux Rope Properties in the Martian Ionosphere: Comparison With Three Types of Formation Mechanisms

Flux ropes are a magnetic field phenomenon characterized by a filament of twisted, helical magnetic field around an axial core. They form in the Martian ionosphere via three distinct mechanisms: Boundary wave instabilities (BWI), external reconnection (ER) between the interplanetary magnetic field and the crustal anomalies, and internal reconnection (IR) of the crustal anomalies themselves. We have identified 121 magnetic flux ropes (FR) from 1900 orbits using plasma and magnetic field measurements measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, and separate FR into categories based on formation mechanism by analyzing electron signatures. We find evidence for flux ropes formed via BWI, ER, and IR mechanisms which comprise 9%, 34%, and 57% of our data‐set, respectively. FR formed via different mechanisms exhibit differences in location and force‐free radius, indicating the formation mechanism of a FR impacts their influence on the Martian plasma environment.Plain Language SummaryMars possess localized magnetic fields that are frozen into the crust of the planet and protrude out into space. On the dayside of Mars, the crustal fields interact with the charged particles and magnetic field lines that are emanating away from the Sun known as the solar wind. The processes involved in this interaction create the Martian “magnetosphere,” and can have a variety of implications on the evolution of the Martian atmosphere. One by‐product of this interaction is a “magnetic flux rope,” (FR) which is a twisted filament of magnetic flux and plasma. FR shows evidence for the reconfiguration of magnetic field lines within the magnetosphere, and lead to atmospheric loss at Mars. Using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we analyze 121 events in which the spacecraft encountered a FR along its orbit around Mars. This is the first study to show evidence for Martian FR having been formed via three distinct formation mechanisms. FR formed via different mechanisms exhibit differences in geographic location and size, indicating the formation mechanism of a FR impacts their influence on the Martian magnetospheric and atmospheric environment.Key PointsFlux ropes form at Mars via three distinct processes: Boundary wave instabilities, external reconnection, and internal reconnectionAcross 1,900 orbits, we identify and analyze 121 magnetic flux ropes (FR) within the ionosphere of Mars using observations from Mars Atmosphere and Volatile EvolutioNUsing electron and magnetic field observations, we separate the FR into three categories based on formation mechanismPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/167770/1/grl62396.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167770/2/grl62396_am.pd