Emirates Mars Mission, the first interplanetary exploration undertaken by an Arab nation, is returning a number of unique observations of Martian dust storms, providing a depth of information and insight into the way in which these storms evolve and spread across huge swathes of the planet.
Hope provides a platform to observe details of the structure and variability of the Martian atmosphere. Coordinated observations made by the EXI camera and the EMIRS infrared spectrometer characterise the thermal state of the surface and lower atmosphere, and provide details of the geographic distribution of dust, water vapor, and water and carbon-dioxide ice clouds over time scales of minutes to days.
EMIRS is an interferometric thermal infrared spectrometer (operating in the 6-40 micron wavelength range) that complements EXI in characterising the lower atmosphere of Mars. EMIRS measurements are used to determine the distribution of lower atmospheric constituents such as dust, water ice and water vapor (presented here as optical depth – related to the amount of aerosols suspended in the atmosphere).
Starting in late December 2021, EXI and EMIRS monitored a rapidly-evolving regional dust storm as it expanded to a size of over several thousand km.
The prominent dark “shark’s fin” feature in the EXI images is known as Syrtis Major. In this area, thin deposits of dark basaltic sand cover the surface of a gently-sloping shield volcano. To the South, the tan circular feature is the Hellas impact basin (the largest crater on Mars – about 2300 km across, and up to 7 km deep) – often shrouded in dust and water-ice clouds. In both the EMIRS and EXI globes, a green star marks a “reference location” (an 85-km diameter impact crater) to visually aid tracking features in both data sets.
On 29 December 2021 (EMM orbit number 153), EXI captured a fully illuminated disk of Mars nearly centred on Syrtis Major. It was mid-winter in the southern hemisphere (Ls = 149°). As is typical for this season, the atmosphere was relatively clear, with only thin water-ice clouds visible over the plains to the east of Syrtis. As is also typical, Hellas appeared to be filled with tannish dust clouds, obscuring deposits of surface ice mantling the southern portion of the basin. The EMIRS observations during this time confirm the relatively thick dust clouds in Hellas but detect only low amounts of suspended dust elsewhere. This set of EXI and EMIRS observations provides a baseline to compare with the subsequent views of Mars obtained over the following two weeks.
On 5 January 2022, EXI obtained the half-illuminated view of Mars — the sun was just setting near the centre of the disk. Apparently forming over the previous week, a massive dust storm (about 2500 km across) was approaching from the east and was partially obscuring Syrtis Major; greyish water-ice clouds are also evident in this storm. Hellas was completely shrouded by dust clouds. The EMIRS observations show the high concentrations of dust in the Syrtis and Hellas dust storms, with a “dust haze” extending far to the east.
On January 7, 2022, this mid-day EXI observation better reveals the extent of the dust haze and greyish water-ice clouds spreading to the east of Syrtis Major and to the north of Hellas. The EMIRS data reveal the increasing thickness of this diffuse dust haze, suggesting the active lifting of dust from the surface extending at least 4000 km eastward from Syrtis Major.
On January 9, 2022, EXI observed a fully illuminated hemisphere centred on Syrtis Major. The dust-lifting has extended to the west, with a discrete multi-lobed dust storm (about 1200 km across) swirling over northwestern Syrtis. The dust haze is very prominent covering the plains eastward from Syrtis. Again, EMIRS reveals the extent of the dust clouds – dramatically portraying the increased dust optical depth from NW of Syrtis all the way to the eastern limb of the map – spanning about 1/3 of the circumference of Mars!
The final time step is for January 14, 2022, EXI shows a late-afternoon (nearing sunset) view of Syrtis Major. No discrete dust storms are visible; instead, a pervasive dust haze partially obscures, and extends eastward from, the entire Syrtis Major/Hellas region. EMIRS data also indicate the thinning of the haze, with the amount of dust significantly reduced. The continuation of the dust veil to fill the Hellas basin is evident in both the EXI image and EMIRS map.
As the Martian season approaches southern spring, dust storm activity typically becomes more pervasive. The Hope observatory is a valuable orbiting asset in documenting the location and evolution of dust storms on the planet, giving unprecedented observations and insight into the nature of these storms and their characterisation.
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