Abstract:Although Mars today possesses a thin atmosphere and a dry environment, many geological features on Mars suggest that the planet used to possess a thick atmosphere and water on the surface. One widely
“…However, many observations have demonstrated that hydrogen escape rates from the Martian upper atmosphere vary seasonally due to seasonal change in vertical water vapor distribution [3][4][5][6][7] . Additionally, recent observations revealed that major dust storms, which expand regionally or globally on Mars, directly transfer water vapor from the lower to the upper atmosphere and rapidly change the vertical water distribution, increasing hydrogen escape [5][6][7][8][9][10][11][12][13] . Because major regional dust storms occur seasonally and global dust storms occasionally on Mars, monitoring Mars' hydrogen upper atmosphere and dust storms is crucial for understanding its water escape mechanisms.…”
Dust storms on Mars play a role in transporting water from its lower to upper atmosphere, seasonally enhancing hydrogen escape. However, it remains unclear how water is diurnally transported during a dust storm and how its elements, hydrogen and oxygen, are subsequently influenced in the upper atmosphere. Here, we use multi-spacecraft and space telescope observations obtained during a major dust storm in Mars Year 33 to show that hydrogen abundance in the upper atmosphere gradually increases because of water supply above an altitude of 60 km, while oxygen abundance temporarily decreases via water ice absorption, catalytic loss, or downward transportation. Additionally, atmospheric waves modulate dust and water transportations, causing alternate oscillations of hydrogen and oxygen abundances in the upper atmosphere. If dust- and wave-driven couplings of the Martian lower and upper atmospheres are common in dust storms, with increasing escape of hydrogen, oxygen will less efficiently escape from the upper atmosphere, leading to a more oxidized atmosphere. These findings provide insights regarding Mars’ water loss history and its redox state, which are crucial for understanding the Martian habitable environment.
“…However, many observations have demonstrated that hydrogen escape rates from the Martian upper atmosphere vary seasonally due to seasonal change in vertical water vapor distribution [3][4][5][6][7] . Additionally, recent observations revealed that major dust storms, which expand regionally or globally on Mars, directly transfer water vapor from the lower to the upper atmosphere and rapidly change the vertical water distribution, increasing hydrogen escape [5][6][7][8][9][10][11][12][13] . Because major regional dust storms occur seasonally and global dust storms occasionally on Mars, monitoring Mars' hydrogen upper atmosphere and dust storms is crucial for understanding its water escape mechanisms.…”
Dust storms on Mars play a role in transporting water from its lower to upper atmosphere, seasonally enhancing hydrogen escape. However, it remains unclear how water is diurnally transported during a dust storm and how its elements, hydrogen and oxygen, are subsequently influenced in the upper atmosphere. Here, we use multi-spacecraft and space telescope observations obtained during a major dust storm in Mars Year 33 to show that hydrogen abundance in the upper atmosphere gradually increases because of water supply above an altitude of 60 km, while oxygen abundance temporarily decreases via water ice absorption, catalytic loss, or downward transportation. Additionally, atmospheric waves modulate dust and water transportations, causing alternate oscillations of hydrogen and oxygen abundances in the upper atmosphere. If dust- and wave-driven couplings of the Martian lower and upper atmospheres are common in dust storms, with increasing escape of hydrogen, oxygen will less efficiently escape from the upper atmosphere, leading to a more oxidized atmosphere. These findings provide insights regarding Mars’ water loss history and its redox state, which are crucial for understanding the Martian habitable environment.
“…So, we can clarify the connection between the outflow of ions and the atmospheric events in the lower atmosphere such as dust storms and water ice clouds. Recent observations by Mars orbiters and space telescopes have revealed the importance of high-altitude water for hydrogen escape to space (e.g., Clarke et al 2014;Chaffin et al 2017;Heavens et al 2018;Aoki et al 2019;Stone et al 2020;Masunaga et al 2020). It has also been suggested that the oxygen loss rate may decrease during a dust storm (Lee et al 2020).…”
Japan Aerospace Exploration Agency (JAXA) plans a Phobos sample return mission (MMX: Martian Moons eXploration). In this study, we review the related works on the past climate of Mars, its evolution, and the present climate and weather to describe the scientific goals and strategies of the MMX mission regarding the evolution of the Martian surface environment. The MMX spacecraft will retrieve and return a sample of Phobos regolith back to Earth in 2029. Mars ejecta are expected to be accumulated on the surface of Phobos without being much shocked. Samples from Phobos probably contain all types of Martian rock from sedimentary to igneous covering all geological eras if ejecta from Mars could be accumulated on the Phobos surface. Therefore, the history of the surface environment of Mars can be restored by analyzing the returned samples. Remote sensing of the Martian atmosphere and monitoring ions escaping to space while the spacecraft is orbiting Mars in the equatorial orbit are also planned. The camera with multi-wavelength filters and the infrared spectrometer onboard the spacecraft can monitor rapid transport processes of water vapor, dust, ice clouds, and other species, which could not be traced by the previous satellites on the sun-synchronous polar orbit. Such time-resolved pictures of the atmospheric phenomena should be an important clue to understand both the processes of water exchange between the surface/underground reservoirs and the atmosphere and the drivers of efficient material transport to the upper atmosphere. The mass spectrometer with unprecedented mass resolution can observe ions escaping to space and monitor the atmospheric escape which has made the past Mars to evolve towards the cold and dry surface environment we know today. Together with the above two instruments, it can potentially reveal what kinds of atmospheric events can transport tracers (e.g., H2O) upward and enhance the atmospheric escape.
Graphical Abstract
“…(2014) who found for their orbit 5,070 that an assumed exobase temperature of 180 K gave n H = 1.4 × 10 5 cm −3 ; Halekas (2017), who found n H ∼ 3 × 10 5 cm −3 for an assumed exobase temperature of 200 K; and Qin (2021), who found temperatures near 200 K and H densities near 8 × 10 4 cm −3 . Other recent studies of H and O in the thermosphere either did not report retrievals or had no data covering northern spring equinox (Bhattacharyya et al., 2015; Chaffin et al., 2018; Chaufray et al., 2008, 2015; Feldman et al., 2011; Masunaga et al., 2020; Qin, 2020). Importantly, we require no modification to the instrument calibration or solar flux to obtain a good model/data match.…”
Section: Model Description and Data Comparisonmentioning
confidence: 99%
“…Hopkins Ultraviolet Telescope (HUT) (Feldman et al, 2000) and Far Ultraviolet Spectroscopic Explorer (Krasnopolsky & Feldman, 2002), with more recent Hisaki measurements giving spatial resolution comparable to the size of the disk (Masunaga et al, 2020). The only spacecraft flyby observation was made by Rosetta/Alice (Feldman et al, 2011), and only the optically thin H coronal 102.6 nm emission far from the disk was analyzed.…”
Water is lost from the Mars upper atmosphere to space as hydrogen and oxygen, both of which can be observed in scattered ultraviolet sunlight at 102.6 nm. We present Emirates Mars Mission Emirates Mars Ultraviolet Spectrometer (EMM/EMUS) insertion orbit observations of this airglow, resolving the independent altitude contributions of H and O for the first time. We present the first airglow modeling of the complete H and O 102.6 nm system and the first 3D azimuthally symmetric modeling of the O emission, retrieving temperatures and densities typical of northern spring. Our model reproduces the emission well above 200 km, but does not incorporate partial frequency redistribution needed to reproduce the observed O brightness at lower altitudes and on the disk. These results support future EMM/EMUS science orbit retrievals of H loss and the use of 102.6 nm observations to constrain planetary atmospheres across the solar system.
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