The appearance of this cloud can be called a return, it has already appeared before. This elongated cloud is composed of water ice, but despite its appearance and location above the volcano, it is not associated with its activity. This airflow is influenced by the “leeward” slope of the volcano – the side that does not face the wind. Pictures of the intriguing phenomenon are published by the European Space Agency.
The photographs of the cloud, which can be up to 1,800 km long, were taken on July 17 and 19 by the visual monitoring camera (VMC) of the Mars Express mission, which has been studying the Red Planet from orbit for the past 16 years.
We have studied this intriguing phenomenon and expected to see such a cloud form. This elongated cloud forms every Martian year. However, we do not yet know if clouds are always so impressive to look at.
Jorge Hernandez-Bernal, PhD at the University of the Basque Country (Spain) and lead author of an ongoing research
The Martian day, or sol, is slightly longer than the Earth’s day and is 24 hours, 39 minutes and 35 seconds. Sol (from the English solar – “solar”) is a sunny day on Mars. The year on the Red Planet consists of 668 Sol, which is approximately 687 days, so the seasons there last twice as long.
The Southern Solstice is the period of the year when the Sun is at its southernmost position in the sky over Mars. This phenomenon is similar to the winter solstice on Earth. In the early morning hours of this period, this fleeting cloud grows in about three hours and quickly disappears after a few hours.
Most spacecraft in orbit around the Red Planet tend to observe it during the day, but Mars Express is in a privileged position to collect and provide important information about this unique effect.
The scale of this huge cloud cannot be seen if your camera has only a narrow field of view or if you only observe during the day. Fortunately for Mars Express, the spacecraft’s highly elliptical orbit, coupled with the VMC’s wide field of view, allows us to capture images covering most of the planet in the early morning.
Eleni Ravanis, trainee graduate of the Mars Express mission that works specifically for the VMC instrument
The Mars Express Science Group is currently referring to this cloud as Arsia Mons Elongated Cloud, AMEC.