A Martian gully formed by disappearing glacial ice?
Click for original image.
Cool image time! The picture to the right, cropped and reduced to post here, was taken on April 30, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the rim of a seventeen-mile wide crater, and was the scientists label a “gully without apron,” meaning that though something has caused material to disappear within that gully, beginning high on the rim wall, there does not appear to be any piled up apron or debris at the gully’s base.
The blue colors imply the possibility of frost within the gully, while the orange suggests dust or coarse surface material.
The cracks emanating away at right angles from the gully’s base suggest glacial ice, which makes sense based on the location.
The white dot northeast of Lyot Crater marks this location on the overview map to the right. At 54 degrees north latitude, finding evidence of glacial ice within this crater would not be surprising, especially as it sits north of the 2,000-mile-long mid-latitude strip I dub glacier country, as almost every image suggests the presence of glaciers.
This location, combined with those cracks, suggests the gully is actually a place where that glacial ice has sublimated away, thus explaining the lack of a debris apron at its base.
Sounds good, eh? Well, the uncertainty of science remains. A paper just published in
Journal of Geophysical Research: Planets took a close look at the orbital radar data gathered by MRO’s SHARAD instrument and found that there could be less ice here near the surface than the features suggest. SHARAD’s radar specifically looks at the immediate surface layers, what the paper calls the “mantle”. From the abstract:
We find that mantle layers have radar characteristics more consistent with a low ice content and properties that greatly reduce the strength of the radar signal. Further, we find radar evidence consistent with mantle layers burying the ends of glacial ice. This study demonstrates that mantle layers on Mars have a wide range of ice contents and ages, with some being less ice rich than their surface characteristics alone might imply.
This result does not mean there is no glacier here, but that the debris on top that protects it has less ice in it than previously thought. In a sense this makes the existence of underground ice in these mid- and high- latitude regions more likely, as the mantle of dust and debris that protects it is more structurally sound.
In this particular case, however, circumstances likely caused that surface mantle to erode away enough that the ice below was exposed to sunlight and sublimated away. Some underground drainage down the rim slope might have also contributed.
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, cropped and reduced to post here, was taken on April 30, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the rim of a seventeen-mile wide crater, and was the scientists label a “gully without apron,” meaning that though something has caused material to disappear within that gully, beginning high on the rim wall, there does not appear to be any piled up apron or debris at the gully’s base.
The blue colors imply the possibility of frost within the gully, while the orange suggests dust or coarse surface material.
The cracks emanating away at right angles from the gully’s base suggest glacial ice, which makes sense based on the location.
The white dot northeast of Lyot Crater marks this location on the overview map to the right. At 54 degrees north latitude, finding evidence of glacial ice within this crater would not be surprising, especially as it sits north of the 2,000-mile-long mid-latitude strip I dub glacier country, as almost every image suggests the presence of glaciers.
This location, combined with those cracks, suggests the gully is actually a place where that glacial ice has sublimated away, thus explaining the lack of a debris apron at its base.
Sounds good, eh? Well, the uncertainty of science remains. A paper just published in
Journal of Geophysical Research: Planets took a close look at the orbital radar data gathered by MRO’s SHARAD instrument and found that there could be less ice here near the surface than the features suggest. SHARAD’s radar specifically looks at the immediate surface layers, what the paper calls the “mantle”. From the abstract:
We find that mantle layers have radar characteristics more consistent with a low ice content and properties that greatly reduce the strength of the radar signal. Further, we find radar evidence consistent with mantle layers burying the ends of glacial ice. This study demonstrates that mantle layers on Mars have a wide range of ice contents and ages, with some being less ice rich than their surface characteristics alone might imply.
This result does not mean there is no glacier here, but that the debris on top that protects it has less ice in it than previously thought. In a sense this makes the existence of underground ice in these mid- and high- latitude regions more likely, as the mantle of dust and debris that protects it is more structurally sound.
In this particular case, however, circumstances likely caused that surface mantle to erode away enough that the ice below was exposed to sunlight and sublimated away. Some underground drainage down the rim slope might have also contributed.
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
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