Majd Mayyasi

Many extreme solar events were observed in May 2024 as the sun was approaching the solar maximum of Solar Cycle 25. We report observations of Martian proton aurora caused by extreme space weather that impacted Mars during 17-21 May. Using data from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, we observe significant and persistent proton aurora activity at Mars, with peak intensities that exceed ~32 kR and emission enhancements that approach 15 kR. We also observe extremely high solar wind proton densities, velocities, and energy fluxes, as well as significantly elevated upstream magnetic field magnitudes and fluctuations during these orbits. The proton aurora events that were caused by this extreme solar activity in May 2024 represent the highest intensity continuous proton aurora detections that have ever been observed by any Mars asset. These observations advance our understanding of the controlling factors that influence major proton aurora activity at Mars.

Gravity waves in the thermosphere of Mars are complex and variable phenomena capable of causing significant changes to processes in the upper atmosphere of Mars, which can affect atmospheric escape. The objective of this study is to determine how dust storm activity, variation in Local Solar Time (LST), and seasonal changes affect thermospheric gravity wave activity. Analyzing in situ neutral Argon density data from the Mars Atmospheric and Volatile EvolutioN (MAVEN) satellite's Neutral Gas and Ion Mass Spectrometer (NGIMS) using a new metric called Mean Integrated Wave Power (MIWP), we measure the strength of the gravity wave activity across five nightside observation data sets (each of 300 orbits) in a variety of dust conditions: three outside of the Martian Dust season with low dust conditions, one during the 2018 Global Dust Storm (GDS), and one during the regional C storm observed in Mars Year (MY) 34. During nominal, low‐dust conditions, we find the MIWP metric, and thereby gravity wave activity, is twice as high post‐midnight as pre‐midnight. This diurnal behavior is seen here first after L _s = . During the 2018 GDS, MIWP at 18:00–22:00 LST is higher when compared to dust‐free conditions, consistent with past studies. However, MIWP at 22:00–06:00 LST is not statistically different from MIWP during low dust activity, suggesting that dust storm‐driven variation in gravity wave activity is secondary to diurnal effects. MIWP during the MY34 regional C storm point toward 2 novel findings: seasonal variation in gravity wave activity and a strong correlation between dust loading and thermospheric gravity wave activity.

Gravity waves in the thermosphere of Mars are complex and variable phenomena capable of causing significant changes to processes in the upper atmosphere of Mars, which can affect atmospheric escape. The objective of this study is to determine how both dust storm activity and variation in Local Solar Time (LST) affect thermospheric gravity wave activity. Analyzing in-situ neutral Argon density data from the Mars Atmospheric and Volatile EvolutioN (MAVEN) satellite’s Neutral Gas and Ion Mass Spectrometer (NGIMS), we measure the strength of the gravity wave activity across five nightside observation datasets in a variety of dust conditions: three outside of the Martian Dust season with nominal, low dust conditions, one during the 2018 Global Dust Storm (GDS), and one during the regional C storm observed in Mars Year (MY) 34. From nominal conditions, we find thermospheric gravity wave activity increases on the nightside, as seen in previous studies, but is twice as high post-midnight as it is pre-midnight. During the 2018 GDS, the thermospheric gravity wave activity observed between 22:00 and 06:00 LST is generally consistent with gravity wave activity observed during nominal dust conditions. Between 18:00 and 22:00, however, gravity wave activity during the 2018 GDS is ~7 times higher than the weak activity seen during these LSTs in nominal dust conditions. A similar effect is observed during the MY 34 regional C storm, during which gravity wave activity increased in step with the global dust loading.

We evaluate for the first time the large-scale influence of the upstream interplanetary magnetic field (IMF) magnitude and orientation on Martian proton aurora. We specifically look at IMF magnitude and orientations to consider how these factors influence the brightness and likelihood of occurrence for proton aurora activity. Ten years of proton auroral observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft (Jakosky et al., 2015) are utilized in this study. We identify a moderate correlation between proton aurora activity and IMF magnitude that varies seasonally, with highest correlations around Mars southern summer solstice when proton aurora activity reaches an annual high. We also identify preferentially increased proton aurora emission enhancements at IMF cone and clock angles consistent with the shape of the Parker spiral at Mars’s heliocentric distance. An increased proton aurora occurrence rate is observed for near- and quasi-radial IMF orientations, however, this correlation is only observed during seasons other than around southern summer solstice, when the hydrogen corona and bow shock are annually decreased. Lastly, proton aurora are observed to exhibit preferentially higher occurrence rates under strong ±Bz orientations, consistent with the findings of recent studies (e.g., Bowers et al., 2023) which identified conditions of increased likelihood for dayside magnetic reconnection at Mars (i.e., between the IMF and Martian crustal fields) for similar altitudes and geographic locations. Thus, our results suggest that dayside magnetic reconnection may influence Martian proton aurora occurrence. These findings enhance our understanding of the interconnected relationship between proton aurora and the Mars magnetic field environment, as well as the upstream IMF’s role as an important driver of Martian proton aurora activity.

To interpret observations of Hydrogen (H) atoms in the altitude profiles of their Lyman-α emissions obtained from the upper atmosphere and exosphere of Mars, it is necessary to assume that there be a supra-thermal (hot) H population. A remote sensor on board the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft can spectrally resolve the contribution of planetary Hydrogen Lyman-α emissions from those of Deuterium Lyman-α emissions to quantify the H contributions alone. These recent high-resolution observations have shown unexpectedly clear spectral signatures of doppler-shifted Hot H obtained from Martian orbit when the instrument line of sight is pointing away from the planet. The resulting spectra have been analyzed to obtain velocity, temperature, brightness, and spatial distribution of supra-thermal H atoms for the first time, as measured from Mars’ orbit. These findings are contextualized for implications on H and H2O escape at Mars.

Mars’ nightside ionosphere is highly variable and poorly understood, with several internal, external, and local factors affecting multiple sources of ionospheric plasma, all combining to drive highly complex behavior. The three primary plasma sources are a) planetary rotation and cross-terminator ion winds transporting dayside plasma to the nightside, particularly at dusk, and impact ionization when magnetic topology connects nightside upper atmosphere to b) dayside suprathermal photoelectrons c) solar wind electrons (accelerated or not) precipitating from the magnetotail. These sources are impacted by different subsets of: season, local time, subsolar longitude, IMF direction (which determines tail draping configuration), solar wind pressure, solar EUV flux, and the local strength and geometry of crustal magnetic fields that combine with global draping patterns to guide electrons toward or away from certain areas. We utilize 130.4 nm auroral observations from the Emirates Mars Ultraviolet Spectrograph, simulations of terminator ion winds, and in situ measurements from MAVEN of ion and electron density and temperature and suprathermal electron precipitation, as well as upstream measurements and proxies of IMF clock angle and solar wind pressure. Analysis reveals some interesting features. First, in regions of weak or no crustal magnetic fields, surprisingly, pre-dawn (~4 am) plasma densities vary by up to a factor of 30 in response to solar EUV varying by only a factor of ~3. Second, 5R aurora occurrence rate in a given region can vary by up to a factor of 7 with IMF orientation, generally highest for southward IMF and lowest for westward IMF, with higher auroral occurrence post-dusk, decreasing toward and past midnight before increasing again towards dawn. A broad diversity of IMF and local time dependence of plasma density and aurora occurrence is observed across Mars’ crustal magnetic fields. The polarity of a given crustal field determines whether its field lines preferentially magnetically connect to dayside ionospheric or nightside magnetotail electron sources in the post-dusk or pre-dawn sectors. These results highlight the complex and dynamic nature of Mars’ magnetic topology in controlling auroral electron access. Future studies integrating two-dimensional ionospheric models with in situ electron measurements with synoptic and limb auroral imaging will further constrain the relative contributions of the many factors controlling Mars’ enigmatic nightside ionosphere.

We compare observations of hydrogen (H) and protons associated with Martian proton aurora activity, co‐evaluating remote sensing and in situ measurements during these events. Following the currently understood relationship between penetrating protons and H energetic neutral atoms (ENAs) in the formation of proton aurora, we observe an expected correlation between the H Lyman‐alpha (Ly‐α) emission enhancement (used herein as a proxy for H‐ENAs) and penetrating proton flux. However, we also observe a notable spread in the trend between these two data sets. We find that this spread is contemporaneous with one of two major impacting events: high dust activity or extreme solar activity. Proton aurora events exhibiting a relative excess in penetrating proton flux compared to Ly‐α enhancement tend to correspond with periods of high dust activity. Conversely, proton aurora events exhibiting a relative deficit of penetrating proton flux compared to Ly‐α enhancement are qualitatively associated with periods of extreme solar activity. Moreover, we find that the largest proton aurora events occur during concurrent dust storm and solar events, primarily due to the compounding intensified increase in H column density above the bow shock. Finally, we present a simplified empirical estimate for Ly‐α emission enhancement during proton aurora events based on the observed penetrating proton flux and a knowledge of local dust/solar activity at the time; this estimate provides a straightforward method for predicting auroral activity when direct observations are not possible or available. The results of this study advance our understanding of the interconnected relationship between H and protons during Martian proton aurora activity.

C⁺ emission is generated by electron impact, dissociative ionization, photoionization, and resonant scattering with carbon-related atoms, molecules, and ions in the Martian ionosphere and thermosphere. The contribution of each mechanism to the emission, however, has not been elucidated due to the difficulty of observation and the fact that a part of the emission cross section is unclear. The current paper isolates the C⁺ emission mechanism using remote-sensing and in situ observations on board Mars Atmosphere and Volatile EvolutioN. Both electron impact and dissociative ionization/photoionization contribute to C⁺ emission below 150 km altitude when the CO density is high, but only dissociative ionization/photoionization contributes to the emission for the low CO density case, while only dissociative ionization/photoionization dominates the emission at altitudes between 150 and 165 km for both CO density cases. It is difficult to estimate the total flux of suprathermal electrons in the ionosphere from remote-sensing observations of C⁺ emission because the contribution of electron impact to C⁺ emission is small. In contrast, C-atom remote-sensing observations might provide a better understanding of the total flux of suprathermal electrons in the ionosphere than C⁺ emission, and global ultraviolet observations could be utilized as a tool for monitoring the ionosphere. The total flux of suprathermal electrons estimated from C-atom emission may be utilized to isolate the contribution of each C⁺ emission process to the brightness more accurately. This suggests that the C⁺ and C-atom emissions might be tracers of spatiotemporal variations in the Martian ionosphere and thermosphere.

Mars’ water history is fundamental to understanding Earth-like planet evolution. Water escapes to space as atoms, and hydrogen atoms escape faster than deuterium giving an increase in the residual D/H ratio. The present ratio reflects the total water Mars has lost. Observations with the Mars Atmosphere and Volatile Evolution (MAVEN) and Hubble Space Telescope (HST) spacecraft provide atomic densities and escape rates for H and D. Large increases near perihelion observed each martian year are consistent with a strong upwelling of water vapor. Short-term changes require processes in addition to thermal escape, likely from atmospheric dynamics and superthermal atoms. Including escape from hot atoms, both H and D escape rapidly, and the escape fluxes are limited by resupply from the lower atmosphere. In this paradigm for the escape of water, the D/H ratio of the escaping atoms and the enhancement in water are determined by upwelling water vapor and atmospheric dynamics rather than by the specific details of atomic escape.

We compare observations of hydrogen (H) and protons associated with Martian proton aurora activity, co-evaluating remote sensing and in situ measurements during these events. Following the currently understood relationship between penetrating protons and H energetic neutral atoms (ENAs) in the formation of proton aurora, we observe an expected correlation between the H Lyman-alpha (Ly-α) emission enhancement (used herein as a proxy for H-ENAs) and penetrating proton flux. However, we observe a notable spread in the trend between these two datasets. We find that this spread is contemporaneous with one of two major impacting events: high dust activity or extreme solar activity. Proton aurora events exhibiting a relative excess in penetrating proton flux compared to Ly-α enhancement tend to correspond with periods of high dust activity. Conversely, proton aurora events exhibiting a relative deficit of penetrating proton flux compared to Ly-α enhancement are qualitatively associated with periods of extreme solar activity. Moreover, we find that the largest proton aurora events occur during concurrent dust storm and solar events, primarily due to the compounding intensified increase in H column density above the bow shock. Finally, we present a simplified empirical estimate for Ly-α emission enhancement during proton aurora events based on observed penetrating proton flux and a knowledge of local dust/solar activity at the time, providing a straightforward method for predicting auroral activity when direct observations are not available. The results of this study advance our understanding of the interconnected relationship between H and protons during Martian proton aurora activity.