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Old Yesterday, 11:41 AM
 
Location: Greenville, SC
4,797 posts, read 3,802,069 times
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Quote:
Originally Posted by fisheye View Post
It all depends on how light and fluffy the fine silt. Try to blow gravel and you don't get very far. But if you try to plow talc or flower you can produce a cloud of fine powder. You cannot analyze everything by looking at a picture.
"The dust that covers the surface of Mars is fine like talcum powder."

https://www.space.com/16895-what-is-mars-made-of.html
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Old Yesterday, 07:44 PM
 
Location: Madison, Alabama
3,809 posts, read 1,870,805 times
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Quote:
Originally Posted by ocpaul20 View Post
Yes, I agree, the quality of these images is terrible, and the folks who designed and specified the cameras on the rovers would be horrified to see them. How any scientist can do science on these images I dont know. The PDS images are not that much better either.
#
No, I have never heard of micro-dust devils either, fisheye suggested the white area might be something to do with dust devils. I suppose small eddys and gusts do blow on the Martian surface, so maybe it's possible. Anyway, there are inconsitensies where the wind on Mars is concerned. The article linked to by fisheye does not really help in explaining how in some circumstances the wind can blow enough to scour the ground and in other circumstances it does not move spherules, debris, and sand into piles behind every rock.

The article says the atmosphere is 1% of Earths which suggests the wind is very weak, yet we have rover "cleaning events" which have in the past supposedly clear all the dust off the rovers solar panels. I have seen the gif posted by NASA showing dust devils moving across the Martian surface too. It all just does not make sense because NASA say or suggest the wind is both strong and weak so which is it?
The wind speed is high (fast) but because it's not very dense, there's not much force behind the wind. So strong (in speed) but weak (in force).

The equation for dynamic pressure is p = 1/2 ρ v**2, where p is the pressure, ρ is the density, and v is speed. Simply stated, if the air density is the same, doubling the wind speed results in a quadrupling of pressure.

Mars air density is about 0.01 that of earth's, so to result in the same wind pressure, the wind speed there would have be 10 times what it is on earth.
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Old Yesterday, 10:44 PM
 
Location: PRC
3,100 posts, read 3,296,402 times
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Quote:
Originally Posted by ocpaul20
The article linked to by fisheye does not really help in explaining how in some circumstances the wind can blow enough to scour the ground and in other circumstances it does not move spherules, debris, and sand into piles behind every rock.
I accept there are huge dust storms on Mars the last one which was reported to have finally killed off Opportunity. What I cannot resolve in my mind is the conflicting properties of the Martian wind.

I understand how the wind is weak and fast as described above by RocketDawg, and I see dust particles blown into small sand dunes.

I do NOT see piles of tiny 5mm spherules in the leeward side of rocks.
I do NOT see wind erosion on rocks (tiny dust particles over millions of years). Think of sand-blasting dust at a rock for millions of years.

So, how is all this explained by:
Quote:
Originally Posted by RocketDawg
The wind speed is high (fast) but because it's not very dense, there's not much force behind the wind. So strong (in speed) but weak (in force).

The equation for dynamic pressure is p = 1/2 ρ v**2, where p is the pressure, ρ is the density, and v is speed. Simply stated, if the air density is the same, doubling the wind speed results in a quadrupling of pressure.

Mars air density is about 0.01 that of earth's, so to result in the same wind pressure, the wind speed there would have be 10 times what it is on earth.
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