dust

Tracking the winds that have turned Mars into a planet of dust

Where does all this dust come from? It’s thought to be the result of erosion caused by the winds. Because the Martian atmosphere is so thin, dust particles can be difficult to move, but larger particles can become more easily airborne if winds are turbulent enough, later taking smaller dust motes with them. Perseverance and previous Mars rovers have mostly witnessed wind vortices that were associated with either dust devils or convection, during which warm air rises.

CaSSIS and HRSC data showed that most dust devils occur in the northern hemisphere of Mars, mainly in the Amazonis and Elysium Planitiae, with Amazonis Planitia being a hotspot. They can be kicked up by winds on both rough and smooth terrain, but they tend to spread farther in the southern hemisphere, with some traveling across nearly that entire half of the planet. Seasonal occurrence of dust devils is highest during the southern summer, while they are almost nonexistent during the late northern fall.

Martian dust devils tend to peak between mid-morning and midafternoon, though they can occur from early morning through late afternoon. They also migrate toward the Martian north pole in the northern summer and toward the south pole during the southern summer. Southern dust devils tend to move faster than those in the northern hemisphere. Movement determined by winds can be as fast as 44 meters per second (about 98 mph), which is much faster than dust devils move on Earth.

Weathering the storm

Dust devils have also been found to accelerate extremely rapidly on the red planet. These fierce storms are associated with winds that travel along with them but do not form a vortex, known as nonvortical winds. It only takes a few seconds for these winds to accelerate to velocities high enough that they’re able to lift dust particles from the ground and transfer them to the atmosphere. It is not only dust devils that do this—the team found that even nonvortical winds lift large amounts of dust particles on their own, more than was previously thought, and create a dusty haze in the atmosphere.

What do planet formation and badminton have in common?

astronomy, astrophysics, badminton, dust, planet-forming disk, planetary formation, protoplanetary disks, Science / Mike M. / October 15, 2024

It might not come as a surprise to learn that Lin is a badminton player. “The experience of playing badminton is really the thing that kick-started the idea and led me to ask the right questions,” he said.

Previous explanations attribute the dust alignment to the magnetic influence of the central star, the physics of which can be complicated and not always intuitive. The beauty of the proposed birdie mechanism is its simplicity. “It’s a very good first step,” said Bing Ren, an astronomer at France’s Côte d’Azur Observatory who wasn’t involved in the study.

Still, the birdie-alignment hypothesis is just that—a hypothesis. To confirm whether it holds water, scientists will need to throw their full observational arsenal at protoplanetary disks, such as viewing them at different wavelengths, to sniff out the finer details of particle-gas interactions.

Tracing invisible gas

Real-life protoplanetary disks are likely more complicated than a uniform squadron of space potatoes suspended in thin air. Ren suspects that the grains come in various shapes, sizes, and speeds. Nevertheless, he says Lin’s study is a good foundation for computer models of interstellar clouds, onto which scientists can tack layers of complexity.

The new research points a way forward for probing protoplanetary disks, particularly gas behavior. Given that the grains trace the gas direction, studying dust organization using existing tools like polarized light can allow scientists to map a disk’s aerodynamic flow. Essentially, these grains are tiny flags that signal where the wind blows.

As granular as the details are, the dust alignment is a small but key step in a grand journey of particle-to-planet progression. The nitty-gritty of a particle’s conduct will determine its fate for millions of years—perhaps the primordial seed will hoover up hydrogen and helium to become a gas giant or amass dust to transform into a terrestrial world like Earth. It all starts with it flailing or keeping steady amid a sea of other specks.

Monthly Notices of the Royal Astronomical Society, 2024. DOI: 10.1093/mnras/stae2248 (About DOIs)

Shi En Kim is a DC-based freelance journalist who writes about health, the environment, technology, and the physical sciences. She and three other journalists founded Sequencer Magazine in early 2024. Occasionally, she creates art to accompany her writings or does it simply for fun. Follow her on Twitter at @goes_by_kim, or see more of her work on her personal website.

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