Search

Using the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere Volatile and Evolution spacecraft (MAVEN), we analyzed data from Mars Year (MY) 32, 34, and 35 to examine the He bulge during the northern winter solstice (Ls ∼ 180–240), specifically focusing on the effects from the planet encircling dust event (PEDE‐2018). He collects on the dawn/nightside winter polar hemisphere of Mars. The seasonal migration of the He bulge has been observed and modeled (M. Elrod et al., 2017, https://doi.org/10.1002/2016JA023482; Gupta et al., 2021, https://doi.org/10.1029/2021JE006976). The MAVEN orbit precesses around Mars allowing for a variety of latitude and local time observations throughout the Martian year. MY 32, 34, and 35 had the best possible opportunities to observe the He bulge during northern winter (Ls ∼ 180–240). NGIMS observations during MY 32 and MY 35 revealed a He bulge from the nightside to dawn in alignment with modeling and previous publications. However, in MY 34, during the PEDE, the He bulge was not present, indicating that the PEDE directly impacted upper atmospheric circulation. Updates in modeling indicate changes in circulation and winds can cause He to shift further north than MAVEN was able to observe. While adding a simple static version of gravity waves to the Mars Global Ionosphere Thermosphere Model model may account for some of the variations in the global circulation during the dust event, other studies (e.g., Yiğit, 2023, https://doi.org/10.1038/s41561-022-01118-7) have posited that the gravity waves during the dust storm were more variable than the initial parameters we have included. Plain Language Summary: Mars is regularly subjected to large dust storms that typically start during the northern winter season. Approximately every 7–10 years these large storms can merge and grow and become planet‐sized dust storms that cover 80%–95% of the surface. These rare and massive planet sized storms last for about a month before slowly dissipating, changing not only the surface of the planet but also the structure and composition of the atmosphere. Mars has regular helium bulges that collect in the cold part of the upper atmosphere (e.g., polar winter regions on the night, dawn side). Global circulation models of the atmosphere have shown this helium bulge as predictable throughout the Martian year. The Mars Atmospheres and Volatiles EvolutioN spacecraft made observations of Helium over the course of 4 Martian years, but during the last major global dust storm, where a Helium bulge in the upper atmosphere should have been observed, no increase in Helium associated with a bulge was observed. This could have implications for the broader impact of regular global dust storms, winds, and upper atmosphere circulation on the Martian atmosphere. Key Points: He collects in the upper atmosphere above the dawn winter polar atmosphere regionHe bulge density is unexpectedly lower in Mars Year (MY) 34 northern winter during the (planet encircling dust event) than other observed northern winters during MY 32 and 35He is a tracer for upper atmosphere circulation and changes in the bulge indicate the circulation changed as shown through modeling [ABSTRACT FROM AUTHOR]

Using data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS), we investigate the horizontal variations in composition of the Martian upper atmosphere. We focus on ratios of Ar, N2, O, He, and H2 to CO2 and their variation with local time, latitude, season, and temperature. These are the first direct measurements of H2 in the upper atmosphere, a species important for the delivery of H to this region because H and H2 escape to space. The NGIMS data nominally cover an altitude range of ∼150–300 km, from near the mesopause to above the exobase. The ratios to CO2 of He and H2 are larger toward the poles and on the nightside of the planet, where the atmosphere is colder and downwelling leads to the enrichment of these lighter species. For example, the H2 to CO2 ratio, at a CO2 density of 1 × 108 cm−3, is observed to increase by a factor of 2.8 from 52.5°S to 72.5°S and by a factor of 5.5 from 3 p.m. to 3 a.m. around the equator. We observe seasonal variation of the Ar to CO2 ratio due to deposition and sublimation of CO2 at the polar ice caps. Finally, we find good agreement between the Ar and N2 to CO2 ratios obtained by the Viking Lander Upper Atmospheric Mass Spectrometers and those obtained by NGIMS, and significant disagreement between the N2 to CO2 ratios obtained by the Imaging Ultraviolet Spectrograph on MAVEN and those obtained by NGIMS. Plain Language Summary: Using data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS), which analyzes components of a gas by their mass, we investigate the composition of the outermost portion of the Martian atmosphere. This region of the atmosphere is important because a part of it escapes to space. We explore the way in which the proportions of Ar, N2, O, He, and H2 vary relative to the main atmospheric gas, CO2, over a Martian day and with temperature, latitude, and season. These are the first direct measurements of H2 in the upper atmosphere of Mars. We find that the proportions of the lightest species, H2 and He, vary substantially throughout the Martian day and with latitude. This variation is caused by transport of these species to cooler regions: the atmosphere on the nightside of the planet and above the poles. We observe seasonal variation in the proportion of Ar, which is due to the conversion of CO2 gas to ice at the polar caps during winter. Finally, we find good agreement between measurements obtained by NGIMS and the NASA Viking missions, but significant disagreement between NGIMS and the MAVEN Imaging Ultraviolet Spectrograph. Key Points: The composition of the upper atmosphere of Mars is investigated using mass spectrometer measurements from Mars Atmosphere and Volatile EvolutioN Neutral Gas and Ion Mass SpectrometerThe variation of the ratios of Ar, N2, O, He, and H2 to CO2 with local time, latitude, and season is measuredAll species show a diurnal variation in density ratio with maxima in the early morning and magnitude inversely correlated with mass [ABSTRACT FROM AUTHOR]

The Neutral Gas and Ion Mass Spectrometer (NGIMS) aboard the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission measures the structure and variability of the Martian upper atmosphere. We use NGIMS density profiles to derive upper atmospheric temperature profiles and investigate the thermal structure of this region. The thermal structure of the upper atmosphere is a critical component of understanding atmospheric loss to space, the main science objective of MAVEN, and measured temperatures serve as inputs to and constraints on photochemical and global circulation models. We describe proper treatment of the NGIMS data and correct for the horizontal motion of the spacecraft. Temperature profiles from week‐long, low‐altitude excursions executed by MAVEN, called Deep Dips, are used to investigate the diurnal variation of the temperature and the thermospheric gradient, which varies between 1.33 ± 0.16 and 2.69 ± 0.33 K km−1 on the dayside. NGIMS measurements acquired on nominal MAVEN orbits over more than a Martian year further elucidate the diurnal and latitudinal variations of the temperature. Diurnal variations of about a factor of 2, from 127 ± 8 to 260 ± 7 K, are observed high in the exosphere, and latitudinal variations of 39 ± 17 K are observed in this region. Comparisons indicate broad agreement between temperatures derived from MAVEN NGIMS with previous in situ and remote sensing observations of upper atmospheric temperatures. NGIMS temperatures are also shown to be consistent with predictions of a 1‐D model which includes solar UV and near IR heating, thermal conduction, and radiative cooling in the CO2   ν2 15‐μm band. Key Points: Temperature profiles derived from MAVEN NGIMS data reveal the thermal structure of the Martian upper atmosphereProper treatment of instrumental effects is discussed, including impact on temperatures at the base of the thermosphereDiurnal variations of 130 K and thermospheric gradients between 1.3 and 2.7 K km−1 are observed [ABSTRACT FROM AUTHOR]