Abstract The MAVEN/Imaging Ultraviolet Spectrograph (IUVS) instrument measures Lyman‐α emissions from interplanetary and Martian hydrogen at the limb and through the extended corona of Mars. In June 2018, a global dust storm (GDS) surrounded Mars for a few months, heating the lower atmosphere and leading to an expansion of the Martian atmosphere. Nightside IUVS observations before and throughout this GDS showed the altitude of CO 2 absorption of Lyman‐α photons in the thermosphere to increase by 4.5±1.0 km on 8 June 2018. This shift is attributed to an increase of the CO 2 density by a factor 1.9±0.2 at 110 km due to the heating of the lower atmosphere. These nightside observations, not previously used to study dust storms, in an altitude range not sampled by other instruments, are consistent with dayside MAVEN observations and allow for more comprehensive determination of the global changes produced by the GDS on the Martian thermosphere.
On 9 October 2009, the Lunar Crater Observation and Sensing Satellite (LCROSS) sent a kinetic impactor to strike Cabeus crater, on a mission to search for water ice and other volatiles expected to be trapped in lunar polar soils. The Lyman Alpha Mapping Project (LAMP) ultraviolet spectrograph onboard the Lunar Reconnaissance Orbiter (LRO) observed the plume generated by the LCROSS impact as far-ultraviolet emissions from the fluorescence of sunlight by molecular hydrogen and carbon monoxide, plus resonantly scattered sunlight from atomic mercury, with contributions from calcium and magnesium. The observed light curve is well simulated by the expansion of a vapor cloud at a temperature of ~1000 kelvin, containing ~570 kilograms (kg) of carbon monoxide, ~140 kg of molecular hydrogen, ~160 kg of calcium, ~120 kg of mercury, and ~40 kg of magnesium.
Observations of the H corona before Venus Express. Diurnal variations derived by PVO. Formation of the hydrogen corona. SPICAV-UV/VEX. Lyman--alpha emission. Forward approach for dayside observations. ObservaEons at the dayside and observaEons at the nightside. Forward approach for shadow observaEons
Aims. We study the soft X-ray emission induced by charge exchange (CX) collisions between solar-wind, highly charged ions and neutral atoms of the Martian exosphere. Methods. A 3D multi species hybrid simulation model with improved spatial resolution (130 km) is used to describe the interaction between the solar wind and the Martian neutrals. We calculated velocity and density distributions of the solar wind plasma in the Martian environment with realistic planetary ions description, using spherically symmetric exospheric H and O profiles. Following that, a 3D test-particle model was developed to compute the X-ray emission produced by CX collisions between neutrals and solar wind minor ions. The model results are compared to XMM-Newton observations of Mars. Results. We calculate projected X-ray emission maps for the XMM-Newton observing conditions and demonstrate how the X-ray emission reflects the Martian electromagnetic structure in accordance with the observed X-ray images. Our maps confirm that X-ray images are a powerful tool for the study of solar wind - planetary interfaces. However, the simulation results reveal several quantitative discrepancies compared to the observations. Typical solar wind and neutral coronae conditions corresponding to the 2003 observation period of Mars cannot reproduce the high luminosity or the corresponding very extended halo observed with XMM-Newton. Potential explanations of these discrepancies are discussed.
<p><strong>Abstract</strong></p> <p>The D/H ratio measured in the Martian atmosphere gives an estimation of the planet&#8217;s water escape rate. We present here a global circulation model including the water isotope HDO and the main physical processes of fractionation. Modeling the D/H cycle accompanies the recent measurements from the ACS spectrometer onboard the orbiter TGO. The comparison between the model outputs and the TGO/ACS observations reveal some discrepancies, in particular during the second half of the martian year, when the escape is supposed to be the most efficient. The present work aims at studying these main differences.</p> <p><strong>Introduction</strong></p> <p>The high value of the Martian D/H ratio, derived from the HDO/H<sub>2</sub>O abundance ratio, in comparison to that of the Earth&#8217;s oceans[1],[2],[3],[4], is an indicator of the large escape of water from Mars over time. Apart from the mass difference between both isotopes, the differential escape of H and D comes from the preferential photolysis of H<sub>2</sub>O over HDO[5] and the preferential condensation of HDO over H<sub>2</sub>O [6],[7],[8]. The NOMAD and ACS instruments onboard ExoMars Trace Gas Orbiter (TGO) have recently provided unprecedented observations of vertical variations in HDO abundance and D/H ratio in the martian atmosphere [9],[10],[11],[12], motivating model development [13],[14]. In particular, TGO data cover the second half (&#8220;dusty season&#8221;) of martian year (MY) 34, which includes a Global Dust Storm (GDS) (Ls 180&#176;-230&#176;) and a regional dust storm (Ls 315&#176;-330&#176;). These dust events have been proven to be of particular importance in the hydrogen escape inventory [12],[15],[16],[17],[18].</p> <p><strong>HDO modeling</strong></p> <p>The D/H ratio measured in the Martian atmosphere gives an estimation of the planet&#8217;s water escape rate. We present here a global circulation model including the water isotope HDO and the main physical processes of fractionation. Modeling the D/H cycle accompanies the recent measurements from the ACS spectrometer onboard the orbiter TGO. The comparison between the model outputs and the TGO/ACS observations reveal some discrepancies, in particular during the second half of the martian year, when the escape is supposed to be the most efficient. The present work aims at studying these main differences. Based on Montmessin et al. 2005[19], Rossi et al. 2021[13] have introduced the HDO cycle in the Mars Planetary Climate Model (Mars PCM), formely known as the LMD Mars Global Climate Model[20]. Vals et al. 2022[21] have recently adapted these implementations to the complete representation of the water ice clouds, including the radiative effect of clouds[22] and microphysics, the latter allowing the modeling of supersaturation[23]. The effect of kinetics in the fractionation by condensation has also been included, as has the photodissociation of HDO and the photochemical reactions of the deuterated species [24],[25],[26]. Rossi et al. 2022[27] have used the improved model to compare with TGO/ACS/MIR retrievals of D/H profiles[28] and revealed some discrepancies, which account for the challenge of reproducing the D/H cycle, depending on key components of the Martian atmosphere such as the water and dust cycles.</p> <p><strong>Preliminary results</strong></p> <p>By comparing the simulations and the observations, we particularly notice an overestimation by the model of water vapor above &#8764;60 km occuring near the GDS in MY34, and an underestimation near perihelion in the southern hemisphere (see Figure 1). The difference in water vapor vertical distribution has a direct impact on the D/H profiles (see Figures 2 and 3). In this work, we want to analyse these differences to eventually propose some model improvements. Further comparisons and results for MY34 and 35 will be shown at the conference.</p> <p><img src="" alt="" width="1103" height="735" /></p> <p>Figure 1: Water vapor volume mixing ratio in ppmv as measured by TGO/ACS/NIR[16] (black) and as computed by the model (red) at different altitude ranges.</p> <p><img src="" alt="" /></p> <p>Figure 2: Water vapor volume mixing ratio, temperature and saturation as measured by TGO/ACS/NIR[16], and D/H profiles as measured by TGO/ACS/MIR[28] (black) and as computed by the model (red) during MY34 between solar longitudes 235&#176;, 245&#176; and latitudes -25&#176;N, 25&#176;N.</p> <p><img src="" alt="" /></p> <p>Figure 3: Same layout as Figure 2 between solar longitudes 270&#176;, 300&#176; and latitudes -60&#176;N, 45&#176; N.</p> <p><strong>References</strong></p> <p>[1] Owen et al.: Science, 240 (4860), 1767-1770, 1988</p> <p>[2] Encrenaz et al.: A&A, 612 , A112, 2018.</p> <p>[3] Krasnopolsky: Icarus, 257 , 377 - 386, 2015</p> <p>[4] Villanueva et al.: Science, 348 (6231), 218&#8211;221, 2015.</p> <p>[5] Cheng et al.: Geophysical Research Letters, 26 (24), 3657-3660, 1999</p> <p>[6] Krasnopolsky: Icarus, (2), 597-602, 2000.</p> <p>[7] Fouchet et al.: Icarus, 144 , 114-123, 2000.</p> <p>[8] Bertaux et al.: Journal of Geophysical Research: Planets, 106 (E12), 32879-32884, 2001.</p> <p>[9] Vandaele et al.: Space Science Reviews, 214 (5), 80, 2018.</p> <p>[10] Vandaele et al.: Nature, 568 (7753), 521-525, 2019.</p> <p>[11] Korablev et al.: Space Science Reviews, 214 , 7, 2018.</p> <p>[12] Korablev et al.: Nature, 568 (7753),517-520, 2019.</p> <p>[13] Rossi et al.: grl , 48 (7), e90962, 2021.</p> <p>[14] Daerden et al.: Journal of Geophysical Research (Planets), 127 (2), e07079, 2022.</p> <p>[15] Aoki et al.: Journal of Geophysical Research (Planets), 124 (12), 3482-3497, 2019.</p> <p>[16] Fedorova et al.: Science, 367 (6475), 297-300, 2020.</p> <p>[17] Neary et al.: Geophysical Research Letters, 47 (7), e84354, 2020.</p> <p>[18] Chaffin et al.: Nature Astronomy, 5 , 1036-1042, 2021.</p> <p>[19] Montmessin et al.: Journal of Geophysical Research, 2005.</p> <p>[20] Forget et al.: JGR, 104:24,155&#8211;24,176, 1999.</p> <p>[21] Vals et al.: Journal of Geophysical Research (Planets), under revision, 2022.</p> <p>[22] Madeleine et al. : Geophys. Res. Lett., 39 , 23202, 2012.</p> <p>[23] Navarro et al.: Journal of Geophysical Research (Planets), 2014.</p> <p>[24] Lef&#232;vre et al.: Journal of Geophysical Research (Planets), 126 (4), 2021.</p> <p>[25] Cheng et al.: Journal of Chemical Physics, 120 (1), 224-229, 2004.</p> <p>[26] Chung et al.: Nuclear Instruments and Methods in Physics Research A, 467 (2002), 1572-1576, 2001.</p> <p>[27] Rossi et al.: Journal of Geophysical Research (Planets), under revision, 2022.</p> <p>[28] Alday et al.: Nature Astronomy, 5, 943-950, 2021.</p>
The IUVS instrument on MAVEN contains an echelle spectrograph with a novel optical design to enable long-aperture measurements of emission lines in the absence of continuum, intended primarily to measure the H and D Ly α emission lines from the martian upper atmosphere. The main scientific goal of the echelle channel is to measure the H and D Ly α emissions that result from resonant scattering of solar emission and to discover how the H and D densities, temperatures, and escape fluxes vary with location, season, topography, etc. The global D/H ratio of the martian atmosphere is roughly 5 times higher than in the terrestrial atmosphere due to the escape of a large volume of water into space, likely early in the history of Mars. Since H atoms escape faster than D atoms, the D/H ratio increases with time as more water is lost. Earth-based IR observations have indicated large variations in the HDO/H2O ratio in the lower atmosphere from location to location, and possible changes with the atmospheric seasonal cycles [Villanueva et al. 2015]. HST and MEX measurements of the H corona of Mars have shown large (order of magnitude) changes in the H exosphere and escape flux with changing seasons and/or heliospheric distance [Clarke et al. 2014; Chaffin et al. 2014]. A series of observations of D and H with the IUVS echelle channel now show a strong trend in the variation of both emissions, with order of magnitude changes in both species in the upper atmosphere. With the added data expected in Fall 2016, we will be able to determine this trend over a full range of martian solar longitude. These results and a comparison with proposed processes that might lead to the observed changes will be presented.
The Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has systematically observed the Martian oxygen exosphere for nearly one Martian year now. The OI 130.4 nm resonance scattering line is observed all the time at the dayside providing unprecedented information on the oxygen content of the Martian upper atmosphere. These variations are important to understand the chemistry, dynamics, energetics and escape processes of the Martian upper atmosphere. Using a radiative transfer model, we have estimated the amount of oxygen in the Martian exosphere needed to reproduce the observations of IUVS during the first Martian year of the mission. In this work, we will present the seasonal variations of the exospheric oxygen density derived from this set of observations and discussed these variations in the frame of global models of the Martian upper atmosphere.
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.
On October 19th 2014, Mars experienced a close encounter with Comet C/2013 A1 (Siding Spring), at a distance of ~138,000 km. The coma washed over Mars and the planet passed directly through the cometary debris stream, producing significant effects in Mars' upper atmosphere. We present here an overview of ionospheric measurements performed during the comet encounter with Mars Express, MAVEN, and Mars Reconnaissance Orbiter. We discuss the comet's influence on the ionosphere through different processes that work at different altitudes: magnetospheric disturbances, impact of cometary pickup ions, and deposition of cometary dust.
