A strange, long, thin cloud cloud has again appeared over the 20-km high Arsia Mons volcano on Mars.
Scientists say the curious plume is not linked to volcanic activity, but forms as airflow is influenced by the side of the volcano that does not face the wind.
These images of the cloud, which can reach up to 1800-km in length, were taken on 17 and 19 July by the Visual Monitoring Camera (VMC) on Mars Express, which has been studying the Red Planet from orbit for the past 16 years.
“We have been investigating this intriguing phenomenon and were expecting to see such a cloud form around now,” said Jorge Hernandez-Bernal, a PhD candidate and lead author of an ongoing study on the mysterious phenomenon, in a European Space Agency (ESA) statement.
“This elongated cloud forms every martian year during this season around the southern solstice, and repeats for 80 days or even more, following a rapid daily cycle. However, we don’t know yet if the clouds are always quite this impressive.”
A martian day, or sol, is slightly longer than an Earth day at 24 hours, 39 minutes and 35 seconds long. A year at the Red Planet consists of 668 sols, approximately 687 days, so the seasons last for twice as long.
The southern solstice is the period of the year when the Sun is in the southernmost position in the martian skies, just like 21 December on Earth. In the early mornings during this period, this fleeting cloud grows for approximately three hours, quickly disappearing again just a few hours later.
The Mars Express science team have now named the cloud the Arsia Mons Elongated Cloud, AMEC.
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