As nearby and familiar as it might seem these days, with rovers on its surface and spacecraft in orbit around it (and even more en route) Mars is very much an alien planet. Its landscapes may resemble parts of Earth but they're much colder and drier, the sun may rise and set in its sky but its light is dimmer... and even the dust in its atmosphere is a bit unexpected, as recently discovered by an international team of researchers.
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Launched June 2. 2003, ESA's Mars Express has been in orbit around Mars for over a decade, studying the Red Planet's terrain, composition, and atmosphere. Recently, at the beginning of Mars' northern summer the spacecraft peered through Mars' thin atmosphere as it eclipsed the sun, giving its SPICAM spectrometer a detailed cross-section of its dusty layers. Using this data, researchers in Moscow and Paris have determined that the dust particles in Mars' atmosphere basically come in two sizes, small and large.
The large variety is made up of water ice and smaller bits of dust, while the small ones are considerably tinier aerosol particles. And even though Mars can be a pretty dusty place (with plenty of ice) the amount of dust in its atmosphere is still much less than what's probably in the room you're sitting in now. Still, even this relatively sparse amount is able to drive the production of ice crystals in Mars' atmosphere, ultimately forming clouds and affecting the climate across the entire planet.
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Although the two sizes of particles were seen over both northern and southern hemispheres, in the north the layer of fine particles stays below 30-40 km while down south it can extend up to 70 km.
What's interesting about these findings is that it indicates there must be processes on Mars that resupply dust particles into the upper atmosphere, as the smallest particles will tend to group together to form larger clusters. It's thought that dust devils - swirling columns of heated air that can rise tens of kilometers from the surface - may inject more fine particles into the atmosphere.
The research was published in the March 2014 edition of the journal Icarus.