Arsia Mons on Mars is one of the highest volcanoes in the solar system – more than twice Mount Everest – and it is the scene of a very peculiar weather phenomenon. Every morning during the spring you can see a long and wide cloud of water ice emerge from the top of the extinct volcano. And now scientists have finally uncovered its secrets.
Published in the Journal of Geophysical Research, the cloud is estimated to be 1,800 kilometers (1,120 miles) long and 150 kilometers (93 miles) wide. Observations have shown that the cloud itself is orographic and forms as a result of the volcano.
With its 20 kilometers (63,360 feet) elevation, Arsia Mons plays a big role in the local weather. Even a planet as dry as Mars has a little bit of moisture in the air. This is channeled along the flanks of the volcanoes and condenses into a cloud at higher and cooler heights.
This phenomenon occurs every morning for several months. Just before sunrise, the cloud begins to form and expand westward at about 600 kilometers (375 miles) per hour at an altitude of 45 kilometers (27 miles). When it reaches its maximum height, it lets go and floats west where it evaporates before noon.
“Although orographic clouds are often observed on Earth, they do not reach such an enormous length and do not exhibit such vibrant dynamics,” co-author Agustin Sánchez-Lavega of the University of the Basque Country said in a statement. “Understanding this cloud gives us a great opportunity to try to simulate the formation of the cloud with models – models that will improve our understanding of climate systems on both Mars and Earth.”
Sánchez-Lavega is the scientific leader of Visual Monitoring Camera, or VMC, one of the instruments onboard the European Space Agency’s Mars Express. Nicknamed “the webcam”, the instrument is a wide-field low-res camera originally used to confirm the separation between Mars Express and the Beagle 2 lander in 2003 and then used for public outreach.
“Recently, however, the VMC was reclassified as a camera for science,” added lead author Jorge Hernández Bernal, also from the University of the Basque Country. “Although it has a low spatial resolution, it has a wide field of view – essential for seeing the big picture at different local times of the day – and is great for tracking the evolution of an element over a long period and in small time steps. As a result, we were able to study the entire cloud over countless life cycles. “
VMC, along with other Mars Express instruments and missions from NASA and the Indian Space Research Organization, has now been able to characterize how this cloud forms, changes and disappears.