A deep south Martian dune with bright patches
Click for full image.
Cool image time! Last week the MRO science team posted a new captioned image entitled “Bright and Dark Dunes” featuring a particularly large single dune in the floor of a 25-mile-wide unnamed crater located at about 68 degrees south latitude. The photo to the right, rotated, cropped, reduced, and color enhanced to post here, shows that dune. According to the caption, written by Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona,
This image shows a large sand dune with bright patches. Martian dunes near the poles often have bright patches in the spring, when seasonal frost is lingering. However, this image is from late summer, when frost is long gone. What is going on here?
A close-up look with [MRO’s high resolution camera] provides some clues. The bright patches are made up of large ridges that look like wind-blown bedforms. Additionally, the bright patches are yellowish in the infrared-red-blue image. In enhanced color, most sand on Mars is blue but dust is yellow. This suggests that the bright bedforms are either built from, or covered by, dust or material with a different composition.
Thus, the bright patches reveal either aspect of the dune’s underlying structure, either inherent in the bedrock itself, or the texture of its surface that allows it to hold more dust. As Dundas adds, “I think more study would be needed to determine the answer in this particular case.”
There are other aspects of this dune that can be seen by a look at the wider view afforded by MRO’s context camera below.
For full images go here and here.
The photos to the right were rotated, cropped and reduced to post here. Both were taken in the early autumn on Mars, just before the seasonal dry ice snow begins to fall and cover everything in the high latitudes above 60 degrees with a mantle of CO2.
Why then was the dark splotch that surrounds the dune lighter in 2019? According to Dundas:
The [2019] image is from after the planet-encircling dust storm of 2018, which may have provided a dust coating. It’s quite likely that there are real brightness variations on the surface between the images, but there can also be differences in atmospheric dust that reduce the apparent contrast.
In other words, while 2018’s dust storm might have put a layer of dust on the dark areas to lighten them, the later image might be lighter overall because of there is a different amount of dust in the atmosphere above that would change the 2018 image’s contrast.
Why there should even be a large black splotch surrounding this large dune however remains unsolved, though the dune in this crater with a dark apron around it seemed vaguely reminiscent to me of features in a different crater — located close to the equator — which scientists think might be evidence of inactive hot springs.
The black cross on the overview map to the right marks the location of today’s image. It is about 1,000 miles south of the pole and sits in Mars’ southern cratered highlands.
The support of my readers through the years has given me the freedom and ability to analyze objectively the ongoing renaissance in space, as well as the cultural changes -- for good or ill -- that are happening across America. Four years ago, just before the 2020 election I wrote that Joe Biden's mental health was suspect. Only in this year has the propaganda mainstream media decided to recognize that basic fact.
Fourteen years ago I wrote that SLS and Orion were a bad ideas, a waste of money, would be years behind schedule, and better replaced by commercial private enterprise. Even today NASA and Congress refuse to recognize this reality.
In 2020 when the world panicked over COVID I wrote that the panic was unnecessary, that the virus was apparently simply a variation of the flu, that masks were not simply pointless but if worn incorrectly were a health threat, that the lockdowns were a disaster and did nothing to stop the spread of COVID. Only in the past year have some of our so-called experts in the health field have begun to recognize these facts.
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Click for full image.
Cool image time! Last week the MRO science team posted a new captioned image entitled “Bright and Dark Dunes” featuring a particularly large single dune in the floor of a 25-mile-wide unnamed crater located at about 68 degrees south latitude. The photo to the right, rotated, cropped, reduced, and color enhanced to post here, shows that dune. According to the caption, written by Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona,
This image shows a large sand dune with bright patches. Martian dunes near the poles often have bright patches in the spring, when seasonal frost is lingering. However, this image is from late summer, when frost is long gone. What is going on here?
A close-up look with [MRO’s high resolution camera] provides some clues. The bright patches are made up of large ridges that look like wind-blown bedforms. Additionally, the bright patches are yellowish in the infrared-red-blue image. In enhanced color, most sand on Mars is blue but dust is yellow. This suggests that the bright bedforms are either built from, or covered by, dust or material with a different composition.
Thus, the bright patches reveal either aspect of the dune’s underlying structure, either inherent in the bedrock itself, or the texture of its surface that allows it to hold more dust. As Dundas adds, “I think more study would be needed to determine the answer in this particular case.”
There are other aspects of this dune that can be seen by a look at the wider view afforded by MRO’s context camera below.
For full images go here and here.
The photos to the right were rotated, cropped and reduced to post here. Both were taken in the early autumn on Mars, just before the seasonal dry ice snow begins to fall and cover everything in the high latitudes above 60 degrees with a mantle of CO2.
Why then was the dark splotch that surrounds the dune lighter in 2019? According to Dundas:
The [2019] image is from after the planet-encircling dust storm of 2018, which may have provided a dust coating. It’s quite likely that there are real brightness variations on the surface between the images, but there can also be differences in atmospheric dust that reduce the apparent contrast.
In other words, while 2018’s dust storm might have put a layer of dust on the dark areas to lighten them, the later image might be lighter overall because of there is a different amount of dust in the atmosphere above that would change the 2018 image’s contrast.
Why there should even be a large black splotch surrounding this large dune however remains unsolved, though the dune in this crater with a dark apron around it seemed vaguely reminiscent to me of features in a different crater — located close to the equator — which scientists think might be evidence of inactive hot springs.
The black cross on the overview map to the right marks the location of today’s image. It is about 1,000 miles south of the pole and sits in Mars’ southern cratered highlands.
The support of my readers through the years has given me the freedom and ability to analyze objectively the ongoing renaissance in space, as well as the cultural changes -- for good or ill -- that are happening across America. Four years ago, just before the 2020 election I wrote that Joe Biden's mental health was suspect. Only in this year has the propaganda mainstream media decided to recognize that basic fact.
Fourteen years ago I wrote that SLS and Orion were a bad ideas, a waste of money, would be years behind schedule, and better replaced by commercial private enterprise. Even today NASA and Congress refuse to recognize this reality.
In 2020 when the world panicked over COVID I wrote that the panic was unnecessary, that the virus was apparently simply a variation of the flu, that masks were not simply pointless but if worn incorrectly were a health threat, that the lockdowns were a disaster and did nothing to stop the spread of COVID. Only in the past year have some of our so-called experts in the health field have begun to recognize these facts.
Your help allows me to do this kind of intelligent analysis. I take no advertising or sponsors, so my reporting isn't influenced by donations by established space or drug companies. Instead, I rely entirely on donations and subscriptions from my readers, which gives me the freedom to write what I think, unencumbered by outside influences.
Please consider supporting my work here at Behind the Black.
You can support me either by giving a one-time contribution or a regular subscription. There are five ways of doing so:
1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.
2. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.
3. A Paypal Donation:
5. Donate by check, payable to Robert Zimmerman and mailed to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652
You can also support me by buying one of my books, as noted in the boxes interspersed throughout the webpage or shown in the menu above. And if you buy the books through the ebookit links, I get a larger cut and I get it sooner.
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