Like a clock, a strange cloud has returned far above the Martian surface.
This long, thin cloud was seen on July 17 and 19 by the Visual Monitoring Camera (VMC) attached to Mars Express, a satellite that has been in orbit around Mars since 2004. These images were made possible by the elliptical orbit of Mars Express and VMC wide-field view, as noted in a European Space Agency Press release.
The cloud is a recurrent feature on Mars, appearing annually over Arsia Mons, a 12.4-mile-high (20-kilometer) volcano located near the Martian equator. The cloud resembles a volcanic plume, but is not associated with any type of volcanic activity. Composed of water ice, the cloud emerges along the leeward slope of the volcano, that is, the side that does not face the prevailing winds.
The Elongated Arsia Mons Cloud, or AMEC as it is called, can reach around 1,110 miles (1,800 km) in length. Incredibly, it can be large enough to be seen by telescopes on Earth, according to ESA.
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“We have been investigating this intriguing phenomenon and we expected to see a cloud of this type at this time,” Jorge Hernández-Bernal, a doctoral candidate at the University of the Basque Country in Spain, said in the ESA press release.
AMEC is formed each year at the time of the planet’s southern summer solstice, when the southern Martian hemisphere receives the greatest amount of natural light. The cloud forms early in the morning, accumulates in the next few hours, and then quickly dissipates. This birth and death weather cycle generally lasts around 80 days.
Hernández-Bernal said “we still don’t know if the clouds are always that impressive,” as AMEC’s close-up observations date back to just 11 years ago.
The last cycle of AMEC it happened two years ago. Mars Express made previous observations in 2015, 2012, and 2009. Seasons on Mars last twice as long as on Earth, as a year on Mars lasts 687 Earth days, hence the long delays between AMEC’s annual cycles.
The formation of these water ice clouds may have something to do with the amount of dust present in the Martian atmosphere, but scientists have a lot to learn about these gigantic elongated clouds, such as when they first appeared and why they form so early in the morning. .
Mars is not the only planet with intriguing clouds. Jupiter’s atmospheric formations are even more striking, with fascinating swirls and twists.
An earlier version of this article incorrectly compared the southern Mars summer solstice to an Earth winter solstice.
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