Abstract
Dust storms, observed in all seasons, are among the most momentous Mars atmosphere activities. The Entry-Descent-Landing (EDL) activity of a Martian landing mission is influenced by local atmospheric conditions, especially the dust storm activity probability. It is of great significance to know well the dust storm situation that China's first Mars mission (Tianwen-1) may encounter in EDL season in the Chryse area, one of the tentative landing areas. Firstly, based on four Martian years’ Mars Orbiter Camera (MOC) Mars Daily Global Maps (MDGMs), 1172 dust storms were identified within Chryse’s 1600 km radius ring with their shape parameters extracted, including center, range and area. Secondly, the daily mean dust storm probability was calculated binned by 1° of solar longitude in the Chryse area during EDL season. Dust storm activity frequency was closely interrelated with the seasonal ebb and flow of the arctic polar ice cap, consequently, most of dust storms occurring in either the cap’s grow or the recession. The dust storm activity in the Chryse area mainly came from the northern polar cap region, Acidalia and Chryse, with some contribution from the southern hemisphere (Argyre and Bosprous) northward. Thirdly, we divided the Chryse area into many square grids of 0.5° and computed the average occurrence probability of dust storm in each grid during EDL season. The dust storm activity probability in space was also in-homogeneous, low in the west and south but high in the east and north, which was mainly affected by three factors: topography, the origin and the path of dust storm sequence. Based on Empirical orthogonal function (EOF) analysis, of the storms in the Chryse area we’ve discovered, 40.5% are cap-edge storms in the northern hemisphere and 17.5% are textured dust storms. Finally, according to the temporal and spatial probability of dust storm activity in the Chryse area during EDL season, we held that the preferred landing time of the Tianwen-1 mission in 2021 was in Ls=18°-65° and three preferred landing areas were selected with low dust storm probability.