Scientists at Sorbonne University in France say they have finally worked out why enormous clouds on Mars appear and then vanish almost in the blink of an eye. The formation and sudden disappearance of these clouds, the researchers note, are tied to the thin atmosphere of the red planet and an unusual physical process.

One of the biggest mysteries about Mars has long been its giant clouds. In 2018, such a cloud was spotted right beside Arsia Mons, a volcano on Mars that rises about 20 kilometres high. The cloud forms every morning in spring and autumn, rapidly stretches up to 1,120 miles and then disappears within moments. Known as the Arsia Mons Elongated Cloud, or AMEC, its behaviour matches no conventional pattern.

Jorge Hernandez-Bernal, a scientist at Sorbonne University, said the mystery was cracked by combining computer modelling with a rule of physics. That rule is usually regarded as theoretical, with no common evidence of it in nature. Once this special theory was added to the computer simulations, the expected AMEC cloud shape began to take form. No earlier evidence of such an event has been found in the atmosphere of Earth or any other planet.

On Earth, clouds typically form through heterogeneous nucleation, in which water vapour condenses on dust particles floating in the atmosphere. On Mars, that rule does not apply. In the study, published in the journal Nature Geoscience, the scientists report that in the case of AMEC, water droplets condense directly, without the help of any particle. Hernandez-Bernal describes this as homogeneous nucleation, in which water vapour turns straight into ice particles or clouds, with no intermediate step in the atmosphere.

When wind passes over the Arsia Mons volcano, a powerful wave is created that pulls moist air several miles upward very quickly. As a result, the temperature of the atmosphere drops by up to 54 degrees Fahrenheit (30 degrees Celsius) within just 10 minutes, and relative humidity reaches extreme levels.

Source: Daily Mail