A Martian crater, ice, and dust devil tracks
Click for original image.
Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on January 2, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It is once again a terrain sample image, taken not for any specific research but to fill a gap in the schedule so as to maintain the camera’s proper temperature.
What this picture shows is that even though Mars has a thin atmosphere that produces dust devils, the propagation of dust devils is not uniform across the red planet’s surface. In this picture there are a lot of devil tracks, going in many different directions. Yet few of the many cool images I post from MRO show this number of tracks. In many cases the ground might not be agreeable to leaving tracks, but that cannot be the entire explanation.
The location of this crater, indicated by the red dot on the global map of Mars to the right, is in the high southern latitudes, at 63 degrees south. It is also located about 600 miles south of the southern edge of Hellas Basin, in a region where ice scarps are found and it is thought that there is a lot of near surface ice below the ground.
Thus, this terrain is likely quite icy. We might even be looking at a glacial ice sheet, covering the entire surface with only a thin layer of dust on top to protect it. The crater itself appears to be partly buried in such a thing. Yet, though I have posted many many MRO photos of similar ice terrain in the high latitudes, few have this many dust devil tracks. Most have none.
There is already evidence in the dry equatorial regions of dark splotches that appear to attract dust devils, for reasons that remain unclear. The most popular explanation is that the dark surface is warmer, and the devils are attracted to that warmth. They in turn scour the surface of dust, making it darker, and therefore reinforce the process.
This theory however doesn’t work at today’s location, in the high icy latitudes. The ground isn’t dark, and the devils don’t seem attracted to any particular area.
It is all a mystery, compelling and baffling, but enormously fun to contemplate.
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 original image.
Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on January 2, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It is once again a terrain sample image, taken not for any specific research but to fill a gap in the schedule so as to maintain the camera’s proper temperature.
What this picture shows is that even though Mars has a thin atmosphere that produces dust devils, the propagation of dust devils is not uniform across the red planet’s surface. In this picture there are a lot of devil tracks, going in many different directions. Yet few of the many cool images I post from MRO show this number of tracks. In many cases the ground might not be agreeable to leaving tracks, but that cannot be the entire explanation.
The location of this crater, indicated by the red dot on the global map of Mars to the right, is in the high southern latitudes, at 63 degrees south. It is also located about 600 miles south of the southern edge of Hellas Basin, in a region where ice scarps are found and it is thought that there is a lot of near surface ice below the ground.
Thus, this terrain is likely quite icy. We might even be looking at a glacial ice sheet, covering the entire surface with only a thin layer of dust on top to protect it. The crater itself appears to be partly buried in such a thing. Yet, though I have posted many many MRO photos of similar ice terrain in the high latitudes, few have this many dust devil tracks. Most have none.
There is already evidence in the dry equatorial regions of dark splotches that appear to attract dust devils, for reasons that remain unclear. The most popular explanation is that the dark surface is warmer, and the devils are attracted to that warmth. They in turn scour the surface of dust, making it darker, and therefore reinforce the process.
This theory however doesn’t work at today’s location, in the high icy latitudes. The ground isn’t dark, and the devils don’t seem attracted to any particular area.
It is all a mystery, compelling and baffling, but enormously fun to contemplate.
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
It is good to remember that at least on Earth the atmospheric convection to power dust devils (and tornadoes) is not the absolute warmth of the ground, but the difference in temperature between the ground layer of air and higher altitude air.
Cooler air over warmer air allows bubbles of warm air to pop up from the ground like virtual hot-air balloons, while the Coriolis effects cause the inflowing airflow to curve and spin. Of course the radically different Martian atmosphere chemistry, density, temperatures, and much lower gravity would all make a quantitative difference from the dust devils of Earth, but the basic physics is probably the same.
Surface features like hills, scarps, and volcanoes probably do the job of triggering vertical displacements from winds just as on Earth.
From a track near the center of the crater it appears that one dust devil split in two. Is that known to happen? What about with Earthly tornadoes?
Michael McNeil: I don’t know if a dust devil can split. I doubt it. What you see here is simply different tracks of different devils that happened to cross in just this manner.