Mars Express data explains seasonal Arsia Mons cloud
A new study using ESA Mars Express observations explains the seasonal Arsia Mons Elongated Cloud on Mars. The cloud appears in southern spring and summer, stretches more than 1,100 miles west of Arsia Mons, and disappears each morning. Researchers found an unexpected formation mechanism, though simulations did not match every detail.
The cloud is tied to Arsia Mons, a volcano rising more than 12 miles. During southern spring and summer—296 sols within Mars’s 669-sol year—winds forced upward by the mountain cool by about 30°C in ten minutes, raising relative humidity. The cloud extends westward over 1,100 miles and vanishes each morning.
Researchers attribute its formation to homogeneous nucleation: water vapor becomes ice particles without dust or salt nuclei. This would require relative humidity over 100,000 times Earth levels. Mars Express cameras, especially HRSC, enabled detailed study after 2018, though simulations did not match every observed detail.
This finding may reshape how planetary scientists model cloud formation, potentially influencing future Mars missions and atmospheric research. Space agencies, researchers, and mission planners could benefit by refining instruments for humidity and cloud observations. The public may gain a more vivid understanding of Mars’s active atmosphere, though practical effects on daily life remain indirect and speculative.