Billions of years ago, Mars' ability to sustain liquid water waned as the solar wind and radiation began to erode the atmosphere. Sputtering is an atmospheric escape process that may have been dominant during earlier epochs of our Sun according to isotopic evidence, but is difficult to detect under current solar conditions. Using over 9 years of data from the Mars Atmosphere and Volatile Evolution mission, we present the first observations of present-day sputtering in the martian upper atmosphere. By correlating argon densities with solar electric fields, we find that sputtered rates of argon are over four times higher than model predictions. We also present evidence of enhanced sputtering during a solar storm, offering a glimpse at more intense conditions in the early solar system. Observationally establishing the role of sputtering in the loss of Mars' atmosphere is critical to understanding the conditions that allowed liquid water to exist on the martian surface and the implications for habitability.

Mirror mode structures are born from a plasma instability driven by a large temperature anisotropy and appear downstream of planetary and interplanetary shocks, in their magnetosheath. As so-called "magnetic bottles" imprisoning dense and hot plasma, they are usually observed downstream of their region of formation, where the anisotropy is large and free energy is available, implying that they are advected with the plasma flow to the detection region. At Earth and other planets, the quasi-perpendicular shock provides the plasma with the necessary heating along the perpendicular direction to the local magnetic field. At Mars, which boasts an extended exosphere, an additional source of temperature anisotropy exists, through unstable ring-beam velocity distributions, that is, through ions locally ionized and subsequently picked up by the local electric fields. We report here for the first time an example of near locally-generated mirror mode structures due to pickup protons at Mars using the full plasma instrument suite on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We present events with mirror modes in quasi-perpendicular and quasi-parallel shock conditions, discuss the locality of their generation and show that, in addition to the classic quasi-perpendicular source of anisotropy, another source exists, that is, unstable pickup protons. The existence at Mars of this extra ion anisotropy-generating mechanism is reminiscent of comets.

Single spacecraft missions do not measure the pristine solar wind continuously because of the spacecrafts' orbital trajectory. The infrequent spatiotemporal cadence of measurement fundamentally limits conclusions about solar wind-magnetosphere coupling throughout the solar system. At Mars, such single spacecraft missions result in limitations for assessing the solar wind's role in causing lower altitude observations such as auroral dynamics or atmospheric loss. In this work, we detail the development of a virtual solar wind monitor from the Mars Atmosphere and Volatile Evolution (MAVEN) mission; a single spacecraft. This virtual solar wind monitor provides a continuous estimate of the solar wind upstream from Mars with uncertainties. We specifically employ Gaussian process regression to estimate the upstream solar wind and uncertainty estimations that scale with the data sparsity of our real observations. This proxy enables continuous solar wind estimation at Mars with representative uncertainties for the majority of the time since since late 2014. We conclude by discussing suggested uses of this virtual solar wind monitor for statistical studies of the Mars space environment and heliosphere.

The North American Monsoon is a seasonal shift in the large-scale circulation that supplies 60-80% of annual rainfall in northwestern Mexico and 30-40% in the US southwest. Regional climate models have shown that summer precipitation prediction over North America is the poorest in the Monsoon region. Most climate models do not account for a crucial mechanism of Monsoon: the boundary layer inversion over the Gulf of California controls the low-level moisture transport. To investigate this mechanism, a set of carefully designed simulations of a regional climate model is used to investigate the dependence of Monsoon precipitation on sea surface temperature (SST) in the Gulf. The results are consistent with enhanced observations from a field campaign and show that warmer Gulf SSTs tend to weaken boundary layer inversion and enhance low-level moisture flux, and as a result, more Monsoon precipitation occurs. This highlights the necessity for climate models to implement the mentioned mechanism.

BackgroundThe ion temperature is a key parameter controlling the structure of planetary ionospheres. In the lower ionosphere, where ion motion is dominated by collisions with neutrals, ion temperatures directly affect collision frequencies. At higher altitudes, in the collisionless regime, ion temperatures influence whether some fraction of the distribution can overcome the planet’s gravity to escape to space. Reliable knowledge of ion temperatures is critical to understanding current ionospheric structures as well as the long-term evolution of planetary atmospheres. For nearly 40 years, the only in-situ measurements of ion temperatures at Mars were obtained from ~375 km to ~120 km altitude during the descents of the Viking landers in 1976 [1]. These measurements were made by retarding potential analyzers. Assumptions about ion composition were required to derive temperatures, and all ion species were assumed to be the same temperature. While this assumption is reasonable in the collisional regime below the exobase (~200 km), mass-dependent electromagnetic acceleration can cause temperatures to diverge at higher altitudes.Until recently, ion temperatures at Mars have primarily been investigated using models. The majority of work has focused on explaining elevated electron temperatures in the upper ionosphere, concluding that a topside heat source (e.g. the solar wind) is required to achieve agreement between modeled profiles and Viking observations [2, 3]. The Combined Atmospheric Photochemistry and Ion Tracing (CAPIT) model reproduced Viking profiles by tracing ion paths while accounting for magnetic fields, major chemical reactions, and wave heating [4]. Models of the solar wind interaction with Mars (e.g. [5],[6]) have traditionally adopted a simplified lower boundary assuming equal electron and ion temperatures, which is significantly in error above ~200 km, in contrast to findings by Matta et al. [7] that different ion species have different temperatures. Recently, Ma et al. [8] showed that the electron pressure gradient significantly affects ion temperatures.Since 2014, comprehensive measurements of the ionosphere above 120 km have been made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter at all local times and most latitudes. Studies based on these data are beginning to revolutionize our understanding of the planet’s ionosphere. In this study, we use data collected by the MAVEN SupraThermal And Thermal Ion Composition (STATIC) instrument to present the first measurements of ion temperature at Mars since the Viking landers. MethodologyWe will present O2+ temperature profiles measured in the Martian ionosphere by STATIC. STATIC measures ion energies from 0.1 eV to 30 keV over a 360°x90° field of view, with mass resolution capable of distinguishing the main ionospheric and escaping species: CO2+, O2+, O+, and H+ [9]. Several instrumental effects contribute to the challenge of extracting ion temperatures from STATIC data, some of which require empirical corrections that are currently being calculated. Three different methods are used to calculate the O2+ temperature using different assumptions which are valid over different, overlapping altitude ranges. These calculations include corrections for spacecraft potential, ion suppression, and instrument response, as well as backscatter, straggling, and molecular fragmentation inside the instrument, among other effects. These calibrations have not been finalized, meaning that the O2+ temperatures presented require further correction.Selection of the best temperature is based on characteristics of the measured distribution. If the population is beam-like (i.e. narrow in energy or angle), then the width of the beam indicates the temperature. However, if the distribution is broad, then calculating moments of the three-dimensional velocity distribution function provides a kinetic temperature, which can be higher than the thermal temperature of the Maxwellian core of the distribution. Once temperatures have been calculated, the data are processed automatically to determine which estimate is the most appropriate. The resulting temperature profiles are largely continuous from MAVEN’s periapsis near 150 km up to altitudes well above 350 km. Results and DiscussionWe present O2+ temperature profiles measured by STATIC when MAVEN’s periapsis occurred close to local noon, midnight, dawn, and dusk. These temperature profiles will be presented alongside the neutral Ar temperature measured by the Neutral Gas and Ion Mass Spectrometer, and the electron temperature measured by the Langmuir Probe and Waves experiment [10, 11]. We use profiles measured on the inbound segment of the orbit to minimize the effect of changing solar zenith angle. In addition, Ar temperatures are only available on the inbound segment. The Ar temperature is expected to be representative of the entire neutral population. At altitudes below ~250 km, the ion distribution is usually dominated by O2+, and we anticipate that all ions will converge to the O2+ temperature.The ion, neutral, and electron temperatures are expected to converge below the exobase, where high collision rates force these populations to equilibrate. Although this thermalization begins to occur below ~200 km, temperature differences between Ar and O2+ persist down to MAVEN’s periapsis of 150 km. The electron temperature is several times higher than the ion temperature in this altitude range, contrary to the assumptions made in most modeling studies.We note differences in profiles measured at different local times. Unsurprisingly, the median periapsis ion temperature at midnight is colder than at noon, reaching ~250 K at noon compared to ~175 K at midnight. Variations in temperature between successive orbits are larger on the nightside than the dayside, indicated by the larger range of temperatures measured on the nightside, which is to be expected due to the patchy, tenuous nature of the nightside ionosphere.Measuring the cold thermal ion temperature at another planet poses many challenges. MAVEN STATIC is the first instrument capable of making such measurements at Mars–indeed, it is the first instrument capable of measuring the ion temperature since the Viking landers. Substantial progress has been made toward deriving ion temperatures from STATIC. Once the necessary calibrations are finalized, O2+ temperatures will be calculated for nearly the entire MAVEN mission, providing a new tool for systematically analyzing the Martian atmosphere.References[1] Hanson et al. https://doi.org/10.1029/JS082i028p04351[2] Shinagawa & Cravens. https://doi.org/10.1029/JA094iA06p06506[3] Cui et al. https://doi.org/10.1002/2014JE004726[4] Andersson et al. https://doi.org/10.1016/j.icarus.2009.07.009[5] Dong et al. https://doi.org/10.1002/2014GL059515[6] Brecht & Ledvina. https://doi.org/10.1016/j.icarus.2009.04.028[7] Matta et al. https://doi.org/10.1016/j.icarus.2013.09.006[8] Ma et al. https://doi.org/10.1029/2019JA027091[9] McFadden et al. https://doi.org/10.1007/s11214-015-0175-6[10] Stone et al. https://doi.org/10.1029/2018JE005559[11] Ergun et al. https://doi.org/10.1002/2015GL06528

On 26 December 2022 the solar wind density dropped by over an order of magnitude and remained low for about a day. We have utilized in-situ plasma measurements made by the Mars Atmosphere and Volatile EvolutioN mission to determine how this change affected the Mars-solar wind interaction. During this time period, on inbound orbit segments, MAVEN sampled the terminator ionosphere, which switched from a magnetized to unmagnetized state immediately following the minimum in solar wind density. The magnetic field amplitude was typically 5-10 nT within the upper ionosphere prior to the event and consistently <1 nT after. During the event the magnetic pressure dominated immediately above the ionosphere while within the ionosphere the ionospheric plasma pressure dominated. The high altitude terminator ionosphere remained in this unmagnetized state throughout the event, suggesting that it was the new equilibrium state of the system. The terminator upper ionosphere returned to its original magnetized state once the solar wind density had recovered. The outbound orbit segments sampled the dayside subsolar region which remained magnetized throughout the event: the magnetization state of the ionosphere varied locally, dependent upon the solar zenith angle and corresponding incident solar wind dynamic pressure. Such conditions are different to the commonly reported unmagnetized ionospheric state at Venus during solar maximum conditions, where the interplanetary magnetic field is repelled from the entire dayside ionosphere. Drastic changes in the upstream solar wind are able to change the Mars-solar wind interaction state on timescales less than one MAVEN orbit (similar to 3.5 hr).

The study of the structure of the Martian shock is crucial to understand its microphysics and it is of special interest to understand the solar wind interaction with an unmagnetized, atmospheric body. The Martian bow shock is a rich example of a supercritical, mass-loaded, collisionless shock and it is one of the smallest of the solar system (both in absolute size and in terms of the solar wind ion gyroradii, of the same order of the curvature radius). This raises questions related to which particle acceleration and energy dissipation mechanism can take place, when its small size means dissipation timescales are too long for a stationary shock to convert the excess kinetic energy into heat. In addition, this shock coexists with ultra-low frequency (ULF) upstream waves, that are generated from the pick-up of exospheric ions. We use MAVEN plasma and magnetic field data to show that the fine structure of the Martian supercritical quasi-perpendicular shock (given by the typical supercritical substructures: the foot, ramp and overshoot) is in many ways comparable with that of the Terrestrial shock, which presents a substantially different solar wind – planet interaction. We observe a shock foot of the order of an upstream ion convected gyroradius, that agrees with the model of specular reflection of foot formation (Woods, 1971; Livesey et al., 1984; Gosling and Thomsen, 1985). Also, we find that the shock ramp is typically very narrow, of the order of a few electron inertial lengths. The presence of a well-defined foot and overshoot confirm the importance of dissipative effects, even in such a small bow shock boundary. In this work we also provide a meticulous analysis methodology that stresses the importance on the correct processing of MAVEN data, and the clarity and consistency of the criteria used in the data selection and analysis. We pay special attention to the determination of the external limit of the entry to the ion foot and the identification of the main and secondary overshoots, where the presence of the ULF waves could mean an erroneous identification of these shock features. We also attempt to assess the non-stationarity of the shock substructures, even with the limitations of a single spacecraft mission, by computing a range of local shock speeds to obtain the substructures spatial widths from the timeseries within an upper and lower value.

Cold plasma of ionospheric origin has recently been found to be a much larger contributor to the magnetosphere of Earth than expected1, 2-3. Numerous competing mechanisms have been postulated to drive ion escape to space, including heating and acceleration by wave-particle interactions4 and a global electrostatic field between the ionosphere and space (called the ambipolar or polarization field)5,6. Observations of heated O+ ions in the magnetosphere are consistent with resonant wave-particle interactions7. By contrast, observations of cold supersonic H+ flowing out of the polar ionosphere8,9 (called the polar wind) suggest the presence of an electrostatic field. Here we report the existence of a +0.55 +/- 0.09 V electric potential drop between 250 km and 768 km from a planetary electrostatic field (E parallel to circle plus = 1.09 +/- 0.17 mu V m-1) generated exclusively by the outward pressure of ionospheric electrons. We experimentally demonstrate that the ambipolar field of Earth controls the structure of the polar ionosphere, boosting the scale height by 271%. We infer that this increases the supply of cold O+ ions to the magnetosphere by more than 3,800%, in which other mechanisms such as wave-particle interactions can heat and further accelerate them to escape velocity. The electrostatic field of Earth is strong enough by itself to drive the polar wind9,10 and is probably the origin of the cold H+ ion population1 that dominates much of the magnetosphere2,3.

Boundaries between space plasmas occur in numerous contexts and scales, from astrophysical jets to planetary magnetospheres. Mass and momentum transport across boundaries poses a fundamental problem in magnetospheric physics. Kelvin–Helmholtz instability (KHI) is a promising mechanism to facilitate transport. Although previous studies have suggested KHI occurrence in various space plasmas, theory predicts that compressibility prevents KHI excitation at boundaries with large density gradients because of previously considered boundary structures where density varies with velocity. Based on the observations of a large density gradient boundary by MAVEN at Mars, where we can observe an extreme case, in this study, we show that it is the entropy, instead of the previously considered density, that varies with the velocity in the real velocity-sheared boundary. The entropy-based boundary structure places the velocity shear in a lower-density region than the traditional density-based structure and weakens the compressibility effect. This new boundary structure thus enables KHI excitation even at large density gradient boundaries, such as at the ionopause of unmagnetized planets and the plasmapause of magnetized planets. The result suggests the ubiquitous occurrence of KHI in the plasma universe and emphasizes its important role in planetary cold plasma escape from unmagnetized planets.

An unusually low density solar wind event was observed in December 2022 moving past both Earth and Mars. The source was traced back to a coronal hole and active region on the Sun's surface. The resulting solar wind lead to the development of a co-rotating interaction region (CIR) and trailing rarefaction region that lasted for multiple solar rotations. Within this structure, the solar wind conditions, including density, velocity, and magnetic field magnitude and orientation drastically changed. In this study we analyze the response of the Martian ionosphere using MAVEN data to these changing solar wind conditions. The low density solar wind region associated with the December event resulted in the expansion of the Martian ionospheric boundaries. We show that the ion composition boundary (ICB) is located at extreme altitudes that are beyond previously observed locations from the MAVEN mission between 2015 and 2018. Furthermore, the boundary between shocked solar wind and the Martian ionosphere identified using electron and ion data moved together on the dayside of the planet with the changing solar wind conditions. However, at the flank region these boundaries do not move together, and we show here that the decoupling of the two boundaries may be the result of a change in the interplanetary magnetic field azimuthal angle. The Sun constantly emits fast moving charged particles into interplanetary space in what is known as the solar wind. In December 2022, a region of fast moving solar wind overtook a region of slower moving solar wind. The fast solar wind acted as a broom sweeping up and compressing the slower wind preceding it. This interaction of two solar wind speeds is observed to rotate with the Sun. Trailing this interaction region is a region of low density solar wind. In December 2022, this type of interplanetary solar wind structure interacted with Mars' electrically charged atmosphere, or ionosphere. Throughout this period, the ionosphere boundary characterized by a transition from solar wind ions to planetary ions moved up and down relative to the planet near dusk. As the rarefaction region passed through the system, the ionosphere expanded to unusually high heights as it was not compressed by the solar wind. However, the flapping of the ionospheric boundary seems to depend on the orientation that the solar wind interacts with Mars. The disappearing solar wind event observed at Mars in December 2022 was caused by a co-rotating interaction region Mars' ionosphere expanded further than previously observed locations between 2015 through 2018 The flank ion composition boundary experiences large fluctuations in altitude after a change in the interplanetary magnetic field direction

We present the results of processing the effects of the powerful Gamma Ray Burst GRB221009A captured by the charged particle detectors (electrostatic analyzers and solid-state detectors) onboard spacecraft at different points in the heliosphere on October 9, 2022. To follow the GRB221009A propagation through the heliosphere we used the electron and proton flux measurements from solar missions Solar Orbiter and STEREO-A; Earth magnetosphere and the solar wind missions THEMIS and Wind; meteorological satellites POES15, POES19, MetOp3; and MAVEN - a NASA mission orbiting Mars. GRB221009A had a structure of four bursts: less intense Pulse 1 - the triggering impulse - was detected by gamma-ray observatories at 131659 UT (near the Earth); the most intense Pulses 2 and 3 were detected on board all the spacecraft from the list, and Pulse 4 detected in more than 500 s after Pulse 1. Due to their different scientific objectives, the spacecraft, which data was used in this study, were separated by more than 1 AU (Solar Orbiter and MAVEN). This enabled tracking GRB221009A as it was propagating across the heliosphere. STEREO-A was the first to register Pulse 2 and 3 of the GRB, almost 100 seconds before their detection by spacecraft in the vicinity of Earth. MAVEN detected GRB221009A Pulses 2, 3, and 4 at the orbit of Mars about 237 seconds after their detection near Earth. By processing the time delays observed we show that the source location of the GRB221009A was at RA 288.5 degrees, Dec 18.5 degrees (J2000) with an error cone of 2 degrees

Abstract The Martian bow shock stands as the first defense against the solar wind and shapes the Martian magnetosphere. Previous studies showed the correlation between the Martian bow shock location and solar wind parameters. Here we present direct evidence of solar wind effects on the Martian bow shock by analyzing Tianwen‐1 and MAVEN data. We examined three cases where Tianwen‐1 data show rapid oscillations of the bow shock, while MAVEN data record changes in solar wind plasma and magnetic field. The results indicate that the bow shock is rapidly compressed and then expanded during the dynamic pressure pulse in the solar wind, and is also oscillated during the IMF rotation. The superposition of variations in multiple solar wind parameters leads to more intensive bow shock oscillation. This study emphasizes the importance of joint observations by Tianwen‐1 and MAVEN for studying the real‐time response of the Martian magnetosphere to the solar wind.

In December 2022, an extremely low-density solar wind stream encountered first the Earth and then Mars, shortly after the radial alignment of the two planets (i.e., Mars opposition). As the low-density stream passed Mars, the properties of the Mars-solar wind interaction changed dramatically in response to the low solar wind Alfvenic Mach number and dynamic pressure. The Martian magnetosphere and its boundaries expanded by thousands of kilometers, extending outside of the nominal average bow shock location. The low upstream Mach number resulted in a low ratio of plasma to magnetic field pressure in the magnetosheath, allowing the formation of a very high but stable ion temperature anisotropy, together with a very low level of electromagnetic instabilities. Meanwhile, the decrease in solar wind dynamic pressure caused the Martian upper ionosphere at the terminator to transition from a magnetized state to an unmagnetized state. This event provides an opportunity to study a unique end-member state of the Mars-solar wind interaction. The solar wind consists of a supersonic flow of hot ionized gas (plasma) from the Sun that flows outward through the solar system. The solar wind interacts with planetary atmospheres and magnetic fields, which form shielded regions known as magnetospheres. The characteristics of the solar wind, including its density and speed, vary over a wide range. The shape, extent, and physical characteristics of planetary magnetospheres in turn respond to these changes in the solar wind. In this work, we study the response of the Martian magnetosphere to an extremely low-density solar wind stream. During the passage of this stream, the Martian magnetosphere expanded by thousands of kilometers, and its physical characteristics changed dramatically. This event reveals a unique outlier state for the Mars-solar wind interaction. An extremely low-density solar wind stream encountered the Earth and Mars just after Mars opposition in December 2022The Martian magnetosheath developed very unusual properties, with a low level of plasma instabilities and a high ion anisotropyThe Martian magnetosphere and its boundaries expanded by thousands of km, extending outside of the location of the nominal bow shock

Like its terrestrial counterpart, the Martian bow shock can exhibit foot, ramp, and overshoot substructures. The shock extent is known to vary with solar wind and season, but it remains an open question whether other features of the bow shock also vary seasonally. By comparing parameters of the shock during different seasons and solar wind conditions, we investigated whether the presence of seasonal planetary ions has any effect on the shock structure. We utilized a series of algorithms to automatically collect and analyze 7056 shock crossings from MAVEN spacecraft data between November 2014 and 2019. We compared the magnetic shock jump and overshoot amplitude as functions of upstream parameters and season. We found that the magnetic shock jump agrees to first order with Rankine-Hugoniot predictions, and that the overshoot amplitude dependence on critical ratio, beta and Alfven Mach number agree with the results of previous studies. These trends are identical for all seasons. We also found that the shock jump and fast Mach number correlate primarily with solar zenith angle, whereas overshoot amplitude correlates primarily with shock extent. We found that the most likely cause of the latter was an unexpected strong correlation between overshoot amplitude and the solar wind flow fast Mach number. The seasonal variability of the Sun-Mars system does not appear to be strongly reflected in the resulting shock structure. The bow shock structure is controlled mainly by the properties of the solar wind, rather than by Mars' location in its orbit around the Sun.

We present the results of processing the effects of the powerful Gamma Ray Burst GRB221009A captured by the charged particle detectors (electrostatic analyzers and solid-state detectors) onboard spacecraft at different points in the heliosphere on October 9, 2022. To follow the GRB221009A propagation through the heliosphere we used the electron and proton flux measurements from solar missions Solar Orbiter and STEREO-A; Earth magnetosphere and the solar wind missions THEMIS and Wind; meteorological satellites POES15, POES19, MetOp3; and MAVEN - a NASA mission orbiting Mars. GRB221009A had a structure of four bursts: less intense Pulse 1 - the triggering impulse - was detected by gamma-ray observatories at 131659 UT (near the Earth); the most intense Pulses 2 and 3 were detected on board all the spacecraft from the list, and Pulse 4 detected in more than 500 s after Pulse 1. Due to their different scientific objectives, the spacecraft, which data was used in this study, were separated by more than 1 AU (Solar Orbiter and MAVEN). This enabled tracking GRB221009A as it was propagating across the heliosphere. STEREO-A was the first to register Pulse 2 and 3 of the GRB, almost 100 seconds before their detection by spacecraft in the vicinity of Earth. MAVEN detected GRB221009A Pulses 2, 3, and 4 at the orbit of Mars about 237 seconds after their detection near Earth. By processing the time delays observed we show that the source location of the GRB221009A was at RA 288.5 degrees, Dec 18.5 degrees (J2000) with an error cone of 2 degrees

The Martian MPB (Magnetic Pileup Boundary) is a key boundary in the Mars/Solar Wind interaction as it is here that part of the momentum and energy from the solar wind plasma are transferred to the planetary plasma. Since this interaction is for the most part collisionless, the transfer is mediated by electric and magnetic fields. The acceleration processes and the interaction of particles with electromagnetic fields operate at spatial scales determined by the ambient particle populations. In particular, in regions with sizes of the order of the ion inertial length (ion scales), the Hall electric field is expected to be dominant.In the present work we combine data from the MAVEN spacecraft along one orbit around Mars and multifluid MHD simulation results to study the role of electric fields, currents and forces at the MPB at ion scales. In particular, we find that the current densities deduced from MAVEN data (J similar to 238 nA/m2) of the same order as the values obtained in the simulation (J similar to 56-156 nA/m2) and that the Hall electric force points sunward in both cases. In addition, we find that in the subsolar MPB current layer the Hall electric field (similar to 3.2 mV/m) dominates over the solar wind convective electric field (similar to 0.4 mV/m) and electron pressure gradient (similar to 0.8 mV/m). These values are consistent with previous results suggesting that the MPB thickness is of the order of the solar wind proton inertial length and support the idea that non ideal terms in Ohm's law must be considered when analysing the dynamics of particles around plasma boundaries with ion scale thicknesses.

Solar extreme ultraviolet (EUV) radiation, the solar wind, and solar energetic particles (SEPs) are variable sources of ionization and heating to the Martian atmosphere. Mars Atmosphere Volatile Evolution’s (MAVEN's) elliptical orbit provides a means to characterize these solar drivers immediately upstream of Mars. We have calculated the energy fluxes of EUV, solar wind, and SEPs while MAVEN is outside of the Martian induced magnetosphere. By time‐averaging observations over 2–5 month periods, we reduced short‐term variability to resolve seasonal and solar cycle trends. For the duration spanning the declining phase of solar cycle 24 and three Mars years, the calculated energy fluxes in units of 109 eV/cm2/s were 650–1,400 for EUV, 77–180 for solar wind ions, 2.4–7.4 for solar wind electrons, 0.01–2.7 for SEP ions, and 0–0.4 for SEP electrons. We estimated the fraction of these energy fluxes that would reach the atmosphere and determined that precipitating particle fluxes on the dayside would need to exceed 1012 eV/cm2/s to compare to EUV. We also predicted that SEPs may impart as much or more energy flux than solar wind electrons on the nightside during periods of strong and weak coronal mass ejection activity. We then discussed and decoupled seasonal variation from the solar drivers to reveal trends and outliers as a function of solar cycle. Finally, we compared MAVEN observations during a weak solar cycle to prior estimates of EUV, solar wind, and SEPs from the young sun, and identified times when MAVEN‐observed peak energy fluxes were close to the steady‐state energy fluxes of the ancient solar system.