Giant Cloud Reappears above Martian Volcano
The Visual Monitoring Camera (VMC) on ESA’s Mars Express spacecraft has captured new images of a giant cloud over the 20-km (12.4-mile) high Arsia Mons volcano, the southernmost in a trio of giant Martian shield volcanoes known collectively as Tharsis Montes.
Named the Arsia Mons Elongated Cloud (AMEC), the cloud can reach up to 1,800 km (1,118 miles) in length.
It is made up of water ice, but despite appearances it is not a plume linked to volcanic activity.
Instead, the curious stream forms as airflow is influenced by the volcano’s ‘leeward’ slope — the side that does not face the wind.
“We have been investigating this intriguing phenomenon and were expecting to see such a cloud form around now,” said Jorge Hernandez-Bernal, a Ph.D. candidate at the University of the Basque Country.
“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.”
The southern solstice is the period of the year when the Sun is in the southernmost position in the Martian skies, just like December 21 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.
Most spacecraft in orbit around mars tend to observe in the afternoon, however Mars Express is in a privileged position to gather and provide crucial information on this unique effect.
“The extent of this huge cloud can’t be seen if your camera only has a narrow field of view, or if you’re only observing in the afternoon,” said Eleni Ravanis, a young graduate trainee for the Mars Express mission.
“Luckily for Mars Express, the highly elliptical orbit of the spacecraft, coupled with the wide field of view of the VMC instrument, lets us take pictures covering a wide area of the planet in the early morning. That means we can catch it!”