We present fast algorithms to automatically estimate the statistical position of the bow shock from spacecraft data, using existing analytical two-dimensional (2D) and three-dimensional (3D) models of the shock surface. We derive expressions of the standoff distances in 2D and 3D and of the normal to the bow shock at any given point on it.
Two simple bow shock detection algorithms are constructed, one solely based on a geometrical predictor from existing models, the other using this predicted position to further refine it with the help of magnetometer data, an instrument flown on many planetary missions.
Both empirical techniques are applicable to any planetary environment with a defined shock structure. Applied to the Martian environment and the NASA/MAVEN mission, the predicted shock position is on average within 0.15 planetary radius $R_p$ of the bow shock crossing. Using the predictor-corrector algorithm, this estimate is further refined to within a few minutes of the true crossing $\approx$0.05 $R_p$).
Between 2014 and 2021, we detect 14,929 clear bow shock crossings, predominantly quasi-perpendicular. Thanks to 2D conic and 3D quadratic fits, we investigate the variability of the shock surface with respect to Mars Years (MY), solar longitude (Ls) and solar EUV flux levels. Although asymmetry in $Y$ and $Z$ Mars Solar Orbital coordinates is on average small, we show that for MY32 and MY35, Ls = [135-225$^\circ$] and high solar flux, it can become particularly noticeable, and is superimposed to the usual North-South asymmetry due in part to the presence of crustal magnetic fields.
We present an in-depth analysis of a time interval when quasi-linear mirror mode structures were detected by magnetic field and plasma measurements as observed by the NASA/Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We employ ion and electron spectrometers in tandem to support the magnetic field measurements and confirm that the signatures are indeed mirror modes. Wedged against the magnetic pile-up boundary, the low-frequency signatures last on average $\sim$10 s with corresponding sizes of the order of 15-30 upstream solar wind proton thermal gyroradii, or 10-20 proton gyrorad…
The first estimation of the incompressible energy cascade rate at magnetohydrodynamic (MHD) scales is obtained in the plasma upstream of the Martian bow shock, using MAVEN observations and an exact relation derived for MHD turbulence. The energy cascade rate is computed for events with and without proton cyclotron wave (PCW) activity, for time intervals when MAVEN was in the solar wind with no magnetic connection to the bow shock. It is shown that the nonlinear cascade of energy at the MHD scales is slightly amplified when PCWs are present in the plasma. The analysis of the normalized cross he…
We report on the local structure of the Martian subsolar Magnetic Pileup Boundary (MPB) from minimum variance analysis of the magnetic field measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft for six orbits. In particular, we detect a well defined current layer within the MPB and provide a local estimate of its current density which results in a sunward Hall electric force. This force accounts for the deflection of the solar wind ions and the acceleration of electrons which carry the interplanetary magnetic field through the MPB into the Magnetic Pileup Region. We find t…
Mars Orbiter MAGnetometer (MOMAG) is a scientifc instrument onboard the orbiter of China's first mission for Mars -- Tianwen-1. It started to routinely measure the magnetic field from the solar wind to magnetic pile-up region surrounding Mars since November 13, 2021. Here we present its in-flight performance and first science results based on the first one and a half months' data. By comparing with the magnetic field data in the solar wind from the Mars Atmosphere and Volatile EvolutioN (MAVEN), the magnetic field by MOMAG is at the same level in magnitude, and the same magnetic structures wit…
The response of Martian ionosphere to the passage of Corotating Interaction Region (CIR) of June 2015 is studied using observations from several instruments aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. An intense CIR arrived at Mars on 22 June 2015, during which the upstream solar wind and interplanetary conditions were monitored by the Solar Wind Ion Analyzer (SWIA), Solar Wind Electron Analyzer (SWEA), Magnetometer (MAG), and Solar Energetic Particle (SEP) instruments aboard MAVEN. The CIR event was characterized by enhancements in solar wind density, velocity, and dyna…
A comprehensive study of Nitric oxide (NO) chemistry in the Martian upper atmosphere is restricted due to the lack of requisite measurements. NO is an abundant form of odd nitrogen species in the Martian lower atmosphere and its density depends on several photochemical processes. We have developed a photochemical model to study the NO density in the dayside of Martian upper atmosphere by accounting for various production and loss mechanisms. By utilizing the Neutral Gas and Ion Mass Spectrometer (NGIMS) on-board Mars Atmosphere and Volatile Evolution (MAVEN) mission measured neutral and ion de…
Direct Observations of Magnetic Reconnection in the Solar Wind Current Sheets near Mars
Boston University（波士顿大学）；Institute for Advanced Study, Princeton（普林斯顿高等研究院）；University of Iowa（爱荷华大学）；Space Sciences Laboratory, University of California, Berkeley（加州大学伯克利分校空间科学实验室）；University of Toulouse（图卢兹大学）；Kyoto University（京都大学）；Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder（科罗拉多大学博尔德分校大气与空间物理实验室）
Atmospheric gravity (buoyancy) waves (GWs) are of great importance for the energy and momentum budget of all planetary atmospheres. Propagating upward waves carry energy and momentum from the lower atmosphere to thermospheric altitudes and re-distribute them there. On Mars, GWs dominate the variability of the thermosphere and ionosphere. We provide a comprehensive climatology of Martian thermospheric GW activity at solar minimum (end of Solar Cycle 24) inferred from measurements by Neutral Gas and Ions Mass Spectrometer on board Mars Atmosphere and Volatile EvolutioN (NGIMS/MAVEN). The results…
We present a statistical analysis on the variability of the incompressible energy cascade rate in the solar wind around Mars, making use of an exact relation for fully developed turbulence and more than five years of Mars Atmosphere and Volatile EvolutioN (MAVEN) observations. Using magnetic field and plasma data, we compute the energy cascade rate in the magnetohydrodynamics (MHD) scales in the pristine solar wind. From our statistical results, we conclude that the incompressible energy cascade rate decreases as the Martian heliocentric distance increases, for each of the three explored Marti…
Impacting the dayside Martian ionosphere from above and below: Effects of the impact of CIRs and ICMEs close to aphelion (April 2021) and during dust storms (June-July 2022) seen with MAVEN ROSE
August 1 to November 15, 2016 period was characterized by the presence of Corotating Interaction Regions (CIRs) and a few weak Coronal Mass Ejections (CMEs) in the heliosphere. In this study we show recurrent energetic electron and proton enhancements observed near Earth (1 AU) and Mars (1.43-1.38 AU) during this period. The observations near Earth are using data from instruments aboard ACE, SOHO, and SDO whereas those near Mars are by the SEP, SWIA, and MAG instruments aboard MAVEN. During this period, the energetic electron fluxes observed near Earth and Mars showed prominent periodic enhanc…
Solar Wind Classifications at Mars using Machine Learning Techniques
West Virginia University（西弗吉尼亚大学）；KU Leuven（荷语鲁汶大学）；University of Colorado Boulder（科罗拉多大学博尔德分校）；University of New Hampshire（新罕布什尔大学）；Boston University（波士顿大学）；University of Illinois at Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）；California Institute of Technology（加州理工学院）；University of Iowa（爱荷华大学）
In a two-week period between February and March of 2015, a series of interplanetary coronal mass ejections (ICMEs) and (solar energetic particles) SEPs made contact with Mars. The interactions were observed by several spacecraft, including Mars Express (MEX), Mars Atmosphere and Volatile Evolution Mission (MAVEN), and Mars Odyssey (MO). The ICME disturbances were characterized by an increase in ion speed, plasma temperature, magnetic field magnitude, and energetic electron flux. Furthermore, increased solar wind density and speeds, unusually high local electron densities and high flow velociti…
Using observations from MAVEN's Neutral Gas and Ion Mass Spectrometer (NGIMS), we characterize the seasonal, solar zenith angle (SZA), and solar flux dependent variations of the O$^+$ peak and the O$^+$/O$_2^+$ ratio in the topside ionosphere of Mars. We find that the O$^+$ peak is between 220-300 km and forms at a roughly constant neutral atmospheric pressure level of 10$^{(-8.7 \pm 0.4)}$ Pa. The O$^+$ peak altitude also decreases with increasing SZA near the terminator and varies sinusoidally with an amplitude of 26 km over a period of one Mars year in response to the changing solar insolat…
Martian bow shocks, the solar wind interacting with an unmagnetized planet, are studied. We theoretically investigated how solar parameters, such as the solar wind dynamic pressure and the solar extreme ultraviolet (EUV) flux, influence the bow shock location, which is still currently not well understood. We present the formula for the location of the bow shock nose of the unmagnetized planet. The bow shock location, the sum of the ionopause location and bow shock standoff distance, is calculated in the gasdynamics approach. The ionopause location is determined using thermal pressure continuit…
Solar cycle 24 is one of the weakest solar cycles recorded, but surprisingly the declining phase of it had a slow CME which evolved without any low coronal signature and is classified as a stealth CME which was responsible for an intense geomagnetic storm at Earth (Dst = -176 nT). The impact of this space weather event on the terrestrial ionosphere has been reported. However,the propagation of this CME beyond 1 au and the impact of this CME on other planetary environments have not been studied so far. In this paper, we analyse the data from Sun-Earth L1 point as well as from the Martian orbit …
Simultaneous Mars-orbit observations reveal Kelvin-Helmholtz instability-driven bulk atmospheric ion escape
Boston University（波士顿大学）；Institute for Advanced Study, Princeton（普林斯顿高等研究院）；Catholic University of America（美利坚天主教大学）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；University of Iowa（爱荷华大学）；University of Colorado（科罗拉多大学）；University of California, Berkeley（加州大学伯克利分校）
Investigation of Martian UV Dayglow Emissions in the Southern Hemisphere during Solar Quiet-time Conditions: Insights from Multi-year MAVEN/IUVS Observations
Mars Exospheric Neutral Composition Analyzer (MENCA) of Mars Orbiter Mission (MOM) measures the \emph{in-situ} neutral upper atmospheric constituents of Mars. Martian lower atmosphere predominated by the presence of $CO_2$ which photo-dissociates into atomic oxygen ($O$) in higher altitudes much near the exobase. Atomic $O$ plays a significant role in invoking the stronger presence of $O_2^+$ in the Martian ionosphere. Primary photo-dissociative species $CO_{2}$, crossover their neutral abundance with atomic $O$ in the collisionless heterogenous atmosphere with varying local solar conditions. …
Automated Classification of Plasma Regions at Mars Using Machine Learning
Department of Electrical and Computer Engineering, Boston University, Boston, MA 02215, USA（波士顿大学电气与计算机工程系，波士顿，马萨诸塞州，02215，美国）；Center for Space Physics, Boston University, Boston, MA 02215, USA（波士顿大学空间物理中心，波士顿，马萨诸塞州，02215，美国）；School of Natural Sciences, Institute for Advanced Study, Princeton, NJ 08540, USA（普林斯顿大学高级研究院自然科学学院，普林斯顿，新泽西州，08540，美国）；Department of Mathematics and Statistics, Boston University, Boston, MA 02215, USA（波士顿大学数学与统计学系，波士顿，马萨诸塞州，02215，美国）
We study the interaction of three solar wind structures, two stream interaction regions and one interplanetary coronal mass ejection, with Mars' plasma environment during 20-27 November 2007. This period corresponds to the solar minimum between the solar cycles 23 and 24 which was characterized by very low values of the solar wind density and dynamic pressure and low IMF magnitude. During that time the Mars-Express orbit was in the terminator plane, while the Earth, Sun, and Mars were almost aligned, so we use the ACE and STEREO probes as solar wind monitors in order to identify and characteri…
We propose a new method to estimate ion escape from unmagnetized planets that combines observations and models. Assuming that upstream solar wind conditions are known, a computer model of the interaction between the solar wind and the planet is executed for different ionospheric ion production rates. This results in different amounts of mass loading of the solar wind. Then we obtain the ion escape rate from the model run that best fit observations of the bow shock location. As an example of the method we estimate the heavy ion escape from Mars on 2015-03-01 to be $2\cdot 10^{24}$ ions per seco…
We study roles of the thermosphere and exosphere on the Martian ionospheric structure and ion escape rates in the process of the solar wind-Mars interaction. We employ a four-species multifluid MHD (MF-MHD) model to simulate the Martian ionosphere and magnetosphere. The $cold$ thermosphere background is taken from the Mars Global Ionosphere Thermosphere Model (M-GITM) and the $hot$ oxygen exosphere is adopted from the Mars exosphere Monte Carlo model - Adaptive Mesh Particle Simulator (AMPS). A total of four cases with the combination of 1D (globally averaged) and 3D thermospheres and exospher…
We inspect the evolution of SIRs from Earth to Mars (distance range 1-1.5 AU) over the declining phase of solar cycle 24 (2014-2018). So far, studies only analyzed SIRs measured at Earth and Mars at different times. We compare existing catalogs for both heliospheric distances and arrive at a clean dataset for the identical time range. This allows a well-sampled statistical analysis and for the opposition phases of the planets an in-depth analysis of SIRs as they evolve with distance. We use in-situ solar wind data from OMNI and the MAVEN spacecraft as well as remote sensing data from SDO. A su…
This observational study demonstrates that the magnitude and location of energization of electrons in the Martian magnetosheath is more complex than previous studies suggest. Electrons in Mars's magnetosheath originate in the solar wind and are accelerated by an electric field when they cross the bow shock. Assuming that this acceleration is localized solely to the shock, the field-aligned electron distributions in the sheath are expected to be highly asymmetric. However, such an asymmetry is not observed in this study. Based on the analysis here, it is suggested that an additional parallel ac…
The Incompressible Magnetohydrodynamic Energy Cascade Rate Upstream of Mars: Effects of the Total Energy and the Cross-Helicity on Solar Wind Turbulence
