by Stan Schultz » Tue Mar 03, 2015 4:22 pm
I admit that I while I spend a lot of time in a variety of deserts and have seen a lot of dust devils, all the ones I've seen have been more or less the same color as the dust they're deviling. So, why on a reddish brown planet and on arguably brown soil is that dust devil white? I might expect a different shade of dust brown because of the sifting effects of the wind (e.g., the deviled dust may be of different origin or composition than the coarser base material), or by an unfamiliar angle of observation (looking down from overhead rather than horizontally from the side). But, snow white is difficult to rationalize.
Snow white suggests that the dust devil is deviling something other than dust. Is it possible that it's sorting out water ice or CO2 crystals from the substrate? Is this why we see no devilish footprint? Could it be that our little devil isn't strong enough to lift "ordinary" dust, sand, and gravel, but is capable of lifting much less dense (i.e., "lighter") water ice or CO2 crystals into the atmosphere? Could it be that the "dust-covered Amazonis Planitia" isn't so dust covered after all, rather being covered with something completely different?
Or, how about water ice melting to a slush or liquid in the sunlight, but remaining concealed and protected in the substrate. Perhaps being held in a quasi-liquid state on the surfaces of ordinary substrate particles. And the adhering layer of water tends to make the substrate particles stick together and not be lifted into the atmosphere by our little dust devil. But, as the dust devil whirls overhead the sudden drop in pressure and/or chaotic winds lifts a bit of the semi-liquid or liquid material out of the substrate and turns it into a mist or vapor. And the sudden, extreme drop in temperature turns that mist or vapor nearly instantaneously into a swirling cloud of ultra-fine, whitish crystals?
Okay, so you don't like my hypotheses. I challenge you to invent better ones!
I admit that I while I spend a lot of time in a variety of deserts and have seen a lot of dust devils, all the ones I've seen have been more or less the same color as the dust they're deviling. So, why on a reddish brown planet and on arguably brown soil is that dust devil white? I might expect a different shade of dust brown because of the sifting effects of the wind (e.g., the deviled dust may be of different origin or composition than the coarser base material), or by an unfamiliar angle of observation (looking down from overhead rather than horizontally from the side). But, snow white is difficult to rationalize.
Snow white suggests that the dust devil is deviling something other than dust. Is it possible that it's sorting out water ice or CO2 crystals from the substrate? Is this why we see no devilish footprint? Could it be that our little devil isn't strong enough to lift "ordinary" dust, sand, and gravel, but is capable of lifting much less dense (i.e., "lighter") water ice or CO2 crystals into the atmosphere? Could it be that the "dust-covered Amazonis Planitia" isn't so dust covered after all, rather being covered with something completely different?
Or, how about water ice melting to a slush or liquid in the sunlight, but remaining concealed and protected in the substrate. Perhaps being held in a quasi-liquid state on the surfaces of ordinary substrate particles. And the adhering layer of water tends to make the substrate particles stick together and not be lifted into the atmosphere by our little dust devil. But, as the dust devil whirls overhead the sudden drop in pressure and/or chaotic winds lifts a bit of the semi-liquid or liquid material out of the substrate and turns it into a mist or vapor. And the sudden, extreme drop in temperature turns that mist or vapor nearly instantaneously into a swirling cloud of ultra-fine, whitish crystals?
Okay, so you don't like my hypotheses. I challenge you to invent better ones! :lol2: