Starship Asterisk*

chuckster wrote:

chuckster wrote:Something you don't hear much discussion of is the way the roughly half-gee gravity on Mars affects Earth-based human intuitions about processes there. Everyone seems caught up in the Moab-type desert terrain and water effect analogies. I once thought that standing on the summit of Olympus Mons would be analogous to standing in open space, since my "intuition" told me that Mars' thin atmosphere would all be thousands of feet lower. I was corrected with the explanation that the low Martian gravity doesn't hug the atmosphere as closely as on Earth, and is therefore more "puffy", and more prevalent at higher elevations.
So, how about tumbling Mulligans ? What part does gravity play in their formation, or resistance to their formation etc etc ?

Good question, Chuckster ! Next question . . . ?

geckzilla wrote:I would venture to say that if no one answers your question, we either don't know the answer or aren't willing to speculate.

Or maybe we didn't think it was a good question. Gravity plays an essential part, since without it, liquids would not flow downhill, atmosphere would vanish, volcanic rocks and meteorites would not fall, Mars would not exist, etc, etc, etc. The atmosphere on Mars may once have been thicker and Mars may once have had a lot of flowing water and Mars was once more volcanic than it appears to be now. No doubt, the lower gravity on Mars, compared with Earth, has an effect, but I doubt that the people who specialise in Martian geology rely too strongly on "Earth-based human intuition". They consider gravity as just one of the parameters in the puzzle. It is a recent photo of an unusual rock of unknown origin and age. I am quite prepared to accept the current scientific consensus that "what caused this roundness remains unknown". One of the nice things about science is that it allows for mulligans. Fore! (And thank you Mactavish.)

Tszabeau wrote:Here's a pic of some objects I found in North Texas. The two rocks on the left are both from Stony Creek and the one on the right I found in my backyard. The one on the left looks, to my untrained eye, to be an example of the "rocking" type of erosion. It has a tiered "nest" and an "egg", so to speak, that fits neatly into the wobbled-out "nest".
I imagine the one in the middle could have been made similarly, to the point it's egg hatched. The one on the right is not, actually, a rock but could be fused bearings or something mundane. It is metallic and harder than lead. The way it's fused reminded me of the "thigh bone" that was spotted on Mars, a while back.
https://www.dropbox.com/s/hoyqcp71uq76p ... s.jpg?dl=0

We'd actually like to be able to see the photo you tried to show us Tszabeau, but the link to your photo is broken.

chuckster wrote:Something you don't hear much discussion of is the way the roughly half-gee gravity on Mars affects Earth-based human intuitions about processes there.

This is fully treated in all the papers that deal with martian geomorphology, geological processes, and flow processes.

BDanielMayfield wrote:

Tszabeau wrote:Here's a pic of some objects I found in North Texas. The two rocks on the left are both from Stony Creek and the one on the right I found in my backyard. The one on the left looks, to my untrained eye, to be an example of the "rocking" type of erosion. It has a tiered "nest" and an "egg", so to speak, that fits neatly into the wobbled-out "nest".
I imagine the one in the middle could have been made similarly, to the point it's egg hatched. The one on the right is not, actually, a rock but could be fused bearings or something mundane. It is metallic and harder than lead. The way it's fused reminded me of the "thigh bone" that was spotted on Mars, a while back.
https://www.dropbox.com/s/hoyqcp71uq76p ... s.jpg?dl=0

We'd actually like to be able to see the photo you tried to show us Tszabeau, but the link to your photo is broken.

Try it now. You can't actually embed an image from dropbox like that.

OKAY Thanks for saying SOMEthing. I'm only 17 posts into this forum, and I know they can get cliquish at times, or maybe I said something in one of those posts that didn't go down well, or whatever.

I have read so many abstract and scholarly posts around here, that I thought perhaps someone had some good thoughts on the subject of how Mars' gravity affects what the rovers are finding, and the geological processes inferred by them. If not, then
I'll sit tight and move on to other APODs !

chuckster wrote:OKAY Thanks for saying SOMEthing. I'm only 17 posts into this forum, and I know they can get cliquish at times, or maybe I said something in one of those posts that didn't go down well, or whatever.

I have read so many abstract and scholarly posts around here, that I thought perhaps someone had some good thoughts on the subject of how Mars' gravity affects what the rovers are finding, and the geological processes inferred by them. If not, then
I'll sit tight and move on to other APODs !

Sorry for being a touch on the rude side, but it is rather obvious that everything on the surface of Mars weighs less than half what it would on the surface of Earth and that friction and other opposing forces are also reduced. All other things being equal (which is not a valid assumption) some geological processes would take more time and some less, compared with Earth. Gravity is just one parameter in the models.

chuckster wrote:

chuckster wrote:Something you don't hear much discussion of is the way the roughly half-gee gravity on Mars affects Earth-based human intuitions about processes there. Everyone seems caught up in the Moab-type desert terrain and water effect analogies. I once thought that standing on the summit of Olympus Mons would be analogous to standing in open space, since my "intuition" told me that Mars' thin atmosphere would all be thousands of feet lower. I was corrected with the explanation that the low Martian gravity doesn't hug the atmosphere as closely as on Earth, and is therefore more "puffy", and more prevalent at higher elevations.
So, how about tumbling Mulligans ? What part does gravity play in their formation, or resistance to their formation etc etc ?

Good question, Chuckster ! Next question . . . ?

geckzilla wrote:I would venture to say that if no one answers your question, we either don't know the answer or aren't willing to speculate.

I liked the main body of your comment Chuckster, and I was thinking of responding, but then moonshine-r's trip down the rabbit hole caused me to lose interest in this thread for a time. I benifited from your story about how you learned about the 'puffiness' of the Marsian atmosphere, so thank you for sharing it. It has helped me to understand how such a thin atmosphere can still kick up and hold up the giant dust storms that Mars is famous for.

Geck was correct in why no one promptly answered your question though.

Intuition is a fine thing to use as an aid to analysis. But don't forget about the analysis.

And according to this article:
http://en.wikipedia.org/wiki/Atmosphere_of_Mars

The atmospheric pressure on top of Olympus Mons (0.03 kPa) is only a twentieth of the Mars average, whereas on top of Mount Everest (33.7 kPa) it is as much as a third of the value at Earth sea level. The pressure on Mars is everywhere lower than the Armstrong limit of 6.25 kPa, below which water boils at human body temperature. (One could argue, I suppose, that if you need a space suit, you're in space.)

Nitpicker wrote:Intuition is a fine thing to use as an aid to analysis. But don't forget about the analysis.

And according to this article:
http://en.wikipedia.org/wiki/Atmosphere_of_Mars

The atmospheric pressure on top of Olympus Mons (0.03 kPa) is only a twentieth of the Mars average, whereas on top of Mount Everest (33.7 kPa) it is as much as a third of the value at Earth sea level. The pressure on Mars is everywhere lower than the Armstrong limit of 6.25 kPa, below which water boils at human body temperature. (One could argue, I suppose, that if you need a space suit, you're in space.)

The Wikipedia gives two points of reference for the atmospheric pressure on Mars:

Peak of Olympus Mons: 30 pascals (0.3 millibars)
Hellas Planitia: 1,155 pascals (11.5 millibars)

And at Earth's Highest and Lowest points

Peak of Mount Everest (8,848 meters above sea level): 33,730 pascals (337.3 millibars)
Dead Sea (423 meters below sea level): 106,200 pascals (1062 millibars)

Tthe altitudes that correspond to pressures of 0.3 millibars and 11.5 millibars are:

11.5 millibars ⇒ 30.125 km = 98,350 feet
0.3 millibars ⇒ 57.150 km = 187,500 feet

So literally on the edge of space

Nitpicker wrote:Intuition is a fine thing to use as an aid to analysis. But don't forget about the analysis.

And according to this article:
http://en.wikipedia.org/wiki/Atmosphere_of_Mars

The atmospheric pressure on top of Olympus Mons (0.03 kPa) is only a twentieth of the Mars average, whereas on top of Mount Everest (33.7 kPa) it is as much as a third of the value at Earth sea level. The pressure on Mars is everywhere lower than the Armstrong limit of 6.25 kPa, below which water boils at human body temperature. (One could argue, I suppose, that if you need a space suit, you're in space.)

Nevertheless, the observation about the martian atmosphere is correct. The scale height of the atmosphere on Mars is 30% greater than that of Earth's... which is why meteor and meteorite production is similar on the two planets, and why aerobraking maneuvers work as they do.

(It sometimes makes sense to compare Olympus Mons and Everest, but other than representing their respective planet's highest points, they have little in common. Olympus Mons is three times higher, with its peak in an entirely different atmospheric regime than the top of Everest. If you were at that peak, you wouldn't even know you were on a mountain based on visual clues, just on a big plain with exceptionally thin air.)

if the Mars Rover had landed in the Dead Sea, would it have found traces of past water ?

ta152h0 wrote:if the Mars Rover had landed in the Dead Sea, would it have found traces of past water ?

If the Mars Rover had landed in the Dead Sea, it would have certainly found traces of current water.

Before it sank and stopped transmitting, anyway.

Glub, glub, glub.

who said there is no humor here ?

ta152h0 wrote:who said there is no humor here ?

Nobody, ever. A few people have complained about some of flippant personalities, actually.

Nitpicker wrote:Intuition is a fine thing to use as an aid to analysis. But don't forget about the analysis.

And according to this article:
http://en.wikipedia.org/wiki/Atmosphere_of_Mars

The atmospheric pressure on top of Olympus Mons (0.03 kPa) is only a twentieth of the Mars average, whereas on top of Mount Everest (33.7 kPa) it is as much as a third of the value at Earth sea level. The pressure on Mars is everywhere lower than the Armstrong limit of 6.25 kPa, below which water boils at human body temperature. (One could argue, I suppose, that if you need a space suit, you're in space.)

Maybe I just don't realize the people I am among here, and I apologize. Won't happen again. There are times when I must just read and absorb what I can. I've always worked in design and drafting departments (aerospace) and the standard notes at the top left of the first sheet of technical drawings starts with the statement "Unless Otherwise Specified :". If Mars gravity is automatically figured into all analysis and speculation around here, then OK, I get it.

Thanks, people.

chuckster wrote:

Nitpicker wrote:Intuition is a fine thing to use as an aid to analysis. But don't forget about the analysis.

And according to this article:
http://en.wikipedia.org/wiki/Atmosphere_of_Mars

The atmospheric pressure on top of Olympus Mons (0.03 kPa) is only a twentieth of the Mars average, whereas on top of Mount Everest (33.7 kPa) it is as much as a third of the value at Earth sea level. The pressure on Mars is everywhere lower than the Armstrong limit of 6.25 kPa, below which water boils at human body temperature. (One could argue, I suppose, that if you need a space suit, you're in space.)

Maybe I just don't realize the people I am among here, and I apologize. Won't happen again. There are times when I must just read and absorb what I can. I've always worked in design and drafting departments (aerospace) and the standard notes at the top left of the first sheet of technical drawings starts with the statement "Unless Otherwise Specified :". If Mars gravity is automatically figured into all analysis and speculation around here, then OK, I get it.

Thanks, people.

I hope you don't let the pickishness of a few commenters here put you off, Chuckster. Nitpicker can't help it. Picking at inacturacies is his thing, so much so that he owns it by his choice of username. He picks a me all the time. But I'm seldom bothered by it because I've often learned more facts from his picks, as was true in this topic. But this discussion about the Marsian atmosphere wouldn't have been nearly as informative without your comments.

Bruce

I don't believe that I was nitpicky in this topic. Just a bit rude. Nitpicker is not my natural state, just my name (based on my first ever post to this forum and a preference for self-deprecation) and an occasional habit, which can sometimes trigger further interesting discussion, but not always.

The original question was "what part does gravity play in the formation of rocks like this?" In amongst the (rather mild) rudeness of my response was a perfectly reasonable answer to the very open ended question, which attempted to engage with the question in a variety of ways. There was even an apology shortly afterwards for my rudeness, after it became apparent that I had offended.

No problems, nitpicker.
The discussions here are too unique in my simple life. I do get jazzed up, though I don't always feel the need to comment, because I may realize I have nothing to add, though the subject matter fascinates me. I often also realize that the insights here are my last stop before I better take astronomy/astrophysics/calculus courses before I open my mouth any further.
Thanks for being there !

Chris Peterson wrote: Nevertheless, the observation about the martian atmosphere is correct. The scale height of the atmosphere on Mars is 30% greater than that of Earth's... which is why meteor and meteorite production is similar on the two planets, and why aerobraking maneuvers work as they do.

(It sometimes makes sense to compare Olympus Mons and Everest, but other than representing their respective planet's highest points, they have little in common. Olympus Mons is three times higher, with its peak in an entirely different atmospheric regime than the top of Everest. If you were at that peak, you wouldn't even know you were on a mountain based on visual clues, just on a big plain with exceptionally thin air.)

I confess I had never heard of the term "scale height" as it pertains to atmospheric pressure, until I read that Wikipedia article on the Atmosphere of Mars. Having now read a bit further, I find it curious that scale height is considered a convenient measurement, given that it is only constant for a constant temperature, and the temperature of the atmosphere varies considerably and non-linearly with altitude, on both Earth and Mars.

Atmospheric Temperature Profile of Earth shown here:
http://en.wikipedia.org/wiki/Atmospheric_temperature

Atmospheric Temperature Profile of Mars shown here:
http://www.windows2universe.org/mars/ex ... ofile.html

By my calculations:
1) the scale height of Earth's atmosphere varies from about 5.6 to 8.6 km and is roughly 7 km where meteors tend to begin to ablate (z ~ 65 km, T ~ 240 K).
2) the scale height of Mars's atmosphere varies from about 4.6 to 10.7 km and is roughly 7 km where meteors tend to begin to ablate (z ~ 120 km, T ~ 130 K).

(Some of my numbers might be a bit off here, they are just quick calculations.)

...

Not related to scale height, but I really like the comparison diagrams showing Olympus Mons against France, Mount Everest and Mauna Kea, here:
http://en.wikipedia.org/wiki/Olympus_Mons