Martian dust devils are one example of the unusual weather found on the Red Planet. A dust devil is a ‘skinny’ whirlwind that on Earth forms when hot air near the surface rises rapidly through a pocket of cooler, lower-pressure air and begins to rotate. This creates a spinning column of air – typically 10-50 metres (33-164 feet) in height – that has enough energy to suck up surface dust.
Martian dust devils are in a different league to those on Earth. Typically 50 times as wide and often several kilometres high – as well as boasting intense rotational energy that can suck up vast quantities of dust and rocks – dust devils on Mars are more akin to supertornadoes. Indeed, they are so powerful that
they leave a visible trail of chaos in their wake, in the form of huge snake-like streaks.
Talking of dust, the dust storms on Mars have the ability to shroud the entire planet in a violent gauze of particulate matter moving at 145 kilometres (90 miles) per hour-plus that can reduce visibility to less than five per cent of that under normal conditions. These epic storms form in the planet’s southern hemisphere during the spring and summer seasons. Activity is first heavily localised, however when the amount of carried dust reaches a critical quantity, the storm rapidly intensifies and spreads, carried to the far-flung reaches of the Red Planet through strong jet streams at speeds commonly in excess of 100 metres (328 feet) per second.
Another prominent feature on Mars that is driven by its seasons is the sublimation (rapid vaporisation) of carbon dioxide ice near the planet’s surface. This occurs when Mars’s seasonal winter caps of frozen carbon dioxide are quickly heated and transformed into vapour in spring. The gaseous CO2 then escapes through gaps in the ice, carrying dust with it, and is spread by local winds over the surface, often into distinctive fan shapes.
Mars also has clouds like Earth. These clouds, however, generally form much higher in the atmosphere than ours (ie 80-100 kilometres/50-62 miles up) and are made of carbon dioxide. They are also very faint, resembling mesopheric clouds, and can only form around minuscule grains blown high into the atmosphere during dust storms.