Study: increase in seasonal Martian streaks after 2018 global dust storm suggests dust not water is their cause
Click for full image.
The uncertainty of science: A just-published survey of Mars following the 2018 global dust storm found that there was a significant increase in the seasonal dark streaks that scientists call recurring slope lineae, providing more evidence that these streaks are not caused by some form of water seepage but instead are related to some dry process.
The map to the right is figure 2 from that paper. The white dots show the candidate lineae that appeared following the 2018 global dust storm. About half were new streaks, not seen previously.
From the paper’s conclusion:
Our results suggest that the presence of freshly deposited dust causes or enhances [lineae] formation. This result may resolve the mystery of why [lineae] occur on some slopes but not others that are largely similar (steep, rocky, and warm). Rather than requiring some unseen variable such as groundwater or salt or ripples, the activity may in part be a function of whether or not sufficient dust is deposited over a slope in each year. The otherwise puzzling recurrence and year‐to‐year variability of [lineae] activity can be explained by variable yearly dust fallout.
For years scientists have puzzled over the cause of these seasonal dark streaks. Their look and nature and presence on slopes strongly suggested to our Earth-based eyes that they were caused by the seepage for some form of liquid brine or water.
The data now shows increasingly that they might be a dry Martian process involving dust. According to this new hypothesis, each year dust accumulates on slopes due to the passage of dust devils and wind. When enough dust piles up and encouraged by the warmer summer temperatures, it then flows downhill as a thin avalanche of dust, staining the surface but not changing the topography significantly. I asked Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona and one of the co-writers of this new paper if this study confirms that the cause of recurring lineae is this dry process. His answer,
The association of high lineae activity with dust storms alone could have many causes. However, there are now multiple lines of evidence that lineae are dry grainflows, such as systematically occurring on angle-of-repose slopes. The correlation with dust storms helps us to understand how those grainflows could be working–possibly because sand is also transported on the surface in the storms, and/or because the presence of a coating of dust on the surface helps to cause flows.
Nothing is yet settled, mostly because the cause of these dark streaks is likely complex with a mixture of factors that might even vary from location to location, depending on the material in the ground. Nonetheless, the data seems to shifting to a dry explanation rather than a liquid one. The number of lineae found inside Valles Marineris, in the arid equatorial regions, favors this dry explanation.
At the same time, the preponderance of lineae at the 30 to 60 degree southern latitudes puts them squarely in the region where a lot of glacial features are found. Thus, the science remains uncertain, though that uncertainty is getting narrower and more refined.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Click for full image.
The uncertainty of science: A just-published survey of Mars following the 2018 global dust storm found that there was a significant increase in the seasonal dark streaks that scientists call recurring slope lineae, providing more evidence that these streaks are not caused by some form of water seepage but instead are related to some dry process.
The map to the right is figure 2 from that paper. The white dots show the candidate lineae that appeared following the 2018 global dust storm. About half were new streaks, not seen previously.
From the paper’s conclusion:
Our results suggest that the presence of freshly deposited dust causes or enhances [lineae] formation. This result may resolve the mystery of why [lineae] occur on some slopes but not others that are largely similar (steep, rocky, and warm). Rather than requiring some unseen variable such as groundwater or salt or ripples, the activity may in part be a function of whether or not sufficient dust is deposited over a slope in each year. The otherwise puzzling recurrence and year‐to‐year variability of [lineae] activity can be explained by variable yearly dust fallout.
For years scientists have puzzled over the cause of these seasonal dark streaks. Their look and nature and presence on slopes strongly suggested to our Earth-based eyes that they were caused by the seepage for some form of liquid brine or water.
The data now shows increasingly that they might be a dry Martian process involving dust. According to this new hypothesis, each year dust accumulates on slopes due to the passage of dust devils and wind. When enough dust piles up and encouraged by the warmer summer temperatures, it then flows downhill as a thin avalanche of dust, staining the surface but not changing the topography significantly. I asked Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona and one of the co-writers of this new paper if this study confirms that the cause of recurring lineae is this dry process. His answer,
The association of high lineae activity with dust storms alone could have many causes. However, there are now multiple lines of evidence that lineae are dry grainflows, such as systematically occurring on angle-of-repose slopes. The correlation with dust storms helps us to understand how those grainflows could be working–possibly because sand is also transported on the surface in the storms, and/or because the presence of a coating of dust on the surface helps to cause flows.
Nothing is yet settled, mostly because the cause of these dark streaks is likely complex with a mixture of factors that might even vary from location to location, depending on the material in the ground. Nonetheless, the data seems to shifting to a dry explanation rather than a liquid one. The number of lineae found inside Valles Marineris, in the arid equatorial regions, favors this dry explanation.
At the same time, the preponderance of lineae at the 30 to 60 degree southern latitudes puts them squarely in the region where a lot of glacial features are found. Thus, the science remains uncertain, though that uncertainty is getting narrower and more refined.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
I’ve been having a long think about this, ( unusual for me, I know ;-) , but the “dark streaks” tend to occur at pretty much the same latitude in the same areas, I am of the mind that perhaps the dust is darker than where it lands, so enables more melt? Or sublimation, or something else? I can’t think of any other reason why a dust storm could facilitate anything that would occur at such a regular level in the slopes of Mars… It’s certainly not random. Any thoughts?
Lee: Read the paper I link to. They go into details, but the gist is that if you have piled up enough dust it will exceed the angle of repose which will cause a grainflow downhill. There is a lot more to it, and many unknowns that make this hypothesis as yet incomplete, but that’s the central concept.