Dustbowl Deserts

The hottest regions of Mars are also the driest for the most part, largely resembling the subtropical and steppe deserts of Earth. The flora and fauna here not only has to adapt to the typical trials of such regions, but also to Mars’ constant threat of extreme dust storms and dust devils.

In a stark contrast to Earth, most sand particles on Mars are small enough to be classified as dust, due to spending potentially a billion years being eroded in dry conditions by nothing but wind. Due to the low gravity, once the wind picks up such a dust particle, it can stay airborne for extraordinary amounts of time and impact the dunes again at an almost horizontal angle. One impact can cause multiple other dust particles to become airborne, which then also throw up more particles each, until the process cascades into a full-blown dust storm. And again, due to the low gravity, even light breezes can sometimes escalate into such storms, which can also last much longer than on Earth and travel great distances, as the arid air prevents the particles from clumping together. Dust storms most commonly occur during perihelion, when Mars receives 40% more solar energy than during aphelion. Although it is actually winter in the northern hemisphere during this time, the extra solar energy creates a highly dynamic atmospheric system across the Martian globe that translates into high winds in the northern lowland. These strong winds consequently animate the eternal sands to create dust storms, which can turn the entire lowland region into an almost literal dustbowl for multiple days, sometimes even weeks. The windspeeds reached during such events can go way over 160 km/h, which is in the range of category-2 hurricanes on Earth, a serious danger to our research facilities, though the force of the winds is weakened by the lower air pressure on Mars.

These dust storms also cool down the northern desert, making its winters harsher than they need to be. The storms form an almost protective envelope, where the dust particles intercept most of the solar energy. While this significantly cools down the surface, in turn it also heats up the upper atmosphere to burningly high temperatures. In some years, this process heats up the northern atmosphere so much that it actually becomes warmer than the summerly southern one and the dustbowls balance this out by flowing into the southern hemisphere, heating its air up as well. This consequently causes stronger winds than usual there, which kick up any unthawed dust over the tundra and eventually results in a global dust storm that can cover the whole planet for nearly two months. Such an event only comes to an end once the dust-envelope has created nearly uniform temperatures across the upper atmosphere of the whole planet, giving the winds no directions to flow towards. Thus they finally settle down and the dust with them. 

Another, common occurrence in the northern desert are dust devils, which can reach far larger sizes (sometimes many kilometres tall and hundreds of meters wide ) than on Earth and thus resemble tornadoes more, though their strong windspeeds of up to 100 km/h are again weakened by the lower air pressure.

Animal life can usually cope with these threats by migrating or burrowing underground to brumate out the danger. For the flora it becomes much more precarious, as photosynthesis is difficult when one’s whole body becomes covered in sun-blocking dust. Arephytes are nearly absent from these deserts, as they possess no adaptations to protect themselves from this threat. Spongisporia and Fractaria, on the other hand, have been able to develop unique pumping systems or wiping cilia with which to clean themselves. Most amazingly, some organisms, including some animals, have found ways to profit off the ever-present dust.

Image Sources:  

• Fig. 2: Insight Mission Images 
• Fig. 3: Jet Propulsion Laboratory