by MarkBour » Tue Sep 24, 2019 10:33 pm
JohnD wrote: ↑Tue Sep 24, 2019 9:58 am
As these are "ringing the Martian North Pole" it's the tops of the dunes that will catch the sunlight first. Yet it's the valleys between the dunes where we see dark sand coming through. Shurley shome mishtake in the explanation?
John
I see your reasoning, but I am still quite prepared to accept that these dunes are indeed near the Martian north pole; that they are thawing; and that the darker regions are exposed sand, moreso than the light, cream-colored regions. This leads me to wonder if I can debate your reasoning.
One thing to consider is that the region is very windy, which is what forms the dunes. So, what happens if some of the sand near the top of the dunes thaws? It will be the most mobile sand in the structure, and the wind will reallocate it to lower elevations. Also, as I look over the image carefully, I do see a lot of darkened regions that I think are high up and near the top of the dunes. I would therefore not describe this image as showing melting only in the valleys. It may appear more like this is the case, due to our mental biases when viewing images. We visually assume that the darker portions are lower, and are shadows. Then again, I have to admit, one sees an awful lot of dark patches that appear to be just next to the base of many of the dunes.
Just some food for thought. Wouldn't it be great to have an entire time-lapse video of this region as it thaws?
[quote=JohnD post_id=295513 time=1569319108 user_id=100329]
As these are "ringing the Martian North Pole" it's the tops of the dunes that will catch the sunlight first. Yet it's the valleys between the dunes where we see dark sand coming through. Shurley shome mishtake in the explanation?
John
[/quote]
I see your reasoning, but I am still quite prepared to accept that these dunes are indeed near the Martian north pole; that they are thawing; and that the darker regions are exposed sand, moreso than the light, cream-colored regions. This leads me to wonder if I can debate your reasoning.
One thing to consider is that the region is very windy, which is what forms the dunes. So, what happens if some of the sand near the top of the dunes thaws? It will be the most mobile sand in the structure, and the wind will reallocate it to lower elevations. Also, as I look over the image carefully, I do see a lot of darkened regions that I think are high up and near the top of the dunes. I would therefore not describe this image as showing melting only in the valleys. It may appear more like this is the case, due to our mental biases when viewing images. We visually assume that the darker portions are lower, and are shadows. Then again, I have to admit, one sees an awful lot of dark patches that appear to be just next to the base of many of the dunes.
Just some food for thought. Wouldn't it be great to have an entire time-lapse video of this region as it thaws?