Starship Asterisk*

by **rstevenson** » Tue Dec 29, 2009 8:57 pm

You're looking at an area there that is most of a kilometer across, so that would be a very big box indeed! I assume any such line would indicate an underlying rock feature of some sort, partly covered by the dunes.

The color is false, made that way in order to more easily delineate subtle differences.

Check out this page for the details. There's lots of links there to more information.

Rob

by **WetMars** » Tue Dec 29, 2009 3:21 pm

On this photo: http://apod.nasa.gov/apod/ap080303.html in the centre of the photo the dune seems "disturbed" by something, as if some big flat box was dragged right to it leaving a sharp disturbed edge right in the middle of the dune/page.
Also, what are those "green" spots or splashes everywhere? The place looks kind of toxic to have life on it.

by **bystander** » Tue Mar 11, 2008 8:53 pm

JohnD wrote:Of course that is nothing like an English muffin, as referred to above. Here is an English Muffin:

I'll take two, please. Hot, with butter!

by **neufer** » Tue Mar 11, 2008 8:29 pm

Charles Dickens : Nicholas Nickleby » Chapter 2
.
'This meeting views with alarm and apprehension,
the existing state of the Muffin Trade in this Metropolis
and its neighbourhood; that it considers the Muffin Boys,
.... [i.e., JohnD & Neufer] as at present constituted,
wholly underserving the confidence of the public; and
that it deems the whole Muffin system alike prejudicial to the
health and morals of the people, and subversive of the best
interests of a great commercial and mercantile community.'

by **JohnD** » Tue Mar 11, 2008 7:18 pm

In the spirit in which the above advice was offered, here is a picture of a blueberry muffin that you may compare with its Martian analogue.

Of course that is nothing like an English muffin, as referred to above.
Here is an English Muffin:

Shot at 2008-03-11

John

by **neufer** » Tue Mar 11, 2008 3:05 pm

JohnD wrote:neufer,
See this page from the Rover website. Shows several pictures featuring 'blueberries' in "near true colour". They are not that blue!
http://marsrover.nasa.gov/gallery/press ... 0318a.html

Early in the missison, "Cornell University astronomer Steve Squyres, the mission's principal science investigator, compared the "spherules" to blueberries inside a muffin." By comparision with their distribution, not their colour!

So 'blueberry' may be a misnomer, that could equally be 'currants', as in currant-bun!

http://en.wikipedia.org/wiki/Redcurrant
http://en.wikipedia.org/wiki/Blackcurrant

A (currant?) "approximate true-color" photo:

<<This approximate true-color image taken by the panoramic camera on the Mars Exploration Rover Opportunity shows a region at the end of the rock outcrop lining the small crater, called "Eagle Crater," where the rover now sits. The sphere-like grains or "blueberries" dotting the rocks in the outcrop can also be seen above the rocks, suggesting that these geologic features have origins beyond Eagle Crater. Data from the panoramic camera's blue, green and red filters were combined to make this image.>>

Discussion at: http://www.marsroverblog.com/discuss-is ... -blue.html
-----------------------------------
I remain somewhat confused but I do appreciate John's help in this matter.
-------------------------------------------------
<<The Muffin Man is a traditional nursery rhyme or children's song
with English origins. The lyrics are as follows, or similar:
.
Do you know the Muffin Man? The Muffin Man, the Muffin Man.
Do you know the Muffin Man, Who lives on Drury Lane?
.
Drury Lane is a street in London, also notable for its theatre. Victorian households had many of their fresh foods delivered; muffins would be delivered door-to-door by a muffin man. The "muffins" were the product known in much of the English-speaking world today as English muffins, not the cupcake-shaped American variety. It could also refer to the darker era when Drury Lane was lined with brothels.>>

by **Andy Wade** » Tue Mar 11, 2008 1:12 pm

JohnD wrote:neufer,
See this page from the Rover website. Shows several pictures featuring 'blueberries' in "near true colour". They are not that blue!
http://marsrover.nasa.gov/gallery/press ... 0318a.html

Early in the missison, "Cornell University astronomer Steve Squyres, the mission's principal science investigator, compared the "spherules" to blueberries inside a muffin." By comparision with their distribution, not their colour!

So 'blueberry' may be a misnomer, that could equally be 'currants', as in currant-bun!

John

Blackadder I, The Queen of Spain's Beard:

Percy: You know, they do say that the Infanta's eyes are more beautiful than the famous Stone of Galveston.
Edmund: Mm! ... What?
Percy: The famous Stone of Galveston, My Lord.
Edmund: And what's that, exactly?
Percy: Well, it's a famous blue stone, and it comes ... from Galveston.
Edmund: I see. And what about it?
Percy: Well, My Lord, the Infanta's eyes are bluer than it, for a start.
Edmund: I see. And have you ever seen this stone?
Percy: (nods) No, not as such, My Lord, but I know a couple of people who have, and they say it's very very blue indeed.
Edmund: And have these people seen the Infanta's eyes?
Percy: No, I shouldn't think so, My Lord.
Edmund: And neither have you, presumably.
Percy: No, My Lord.
Edmund: So, what you're telling me, Percy, is that something you have never seen is slightly less blue than something else you have never seen?
Percy: (finally begins to grasp) Yes, My Lord.

by **JohnD** » Tue Mar 11, 2008 1:03 pm

neufer,
See this page from the Rover website. Shows several pictures featuring 'blueberries' in "near true colour". They are not that blue!
http://marsrover.nasa.gov/gallery/press ... 0318a.html

Early in the missison, "Cornell University astronomer Steve Squyres, the mission's principal science investigator, compared the "spherules" to blueberries inside a muffin." By comparision with their distribution, not their colour!

So 'blueberry' may be a misnomer, that could equally be 'currants', as in currant-bun!

John

by **neufer** » Tue Mar 11, 2008 12:42 pm

JohnD wrote:neufer,
Note that many Mars Rover pictures are displayed in "false-colour", that exaggerates the colour differences markedly. The eyeball appearance would be a near uniform brown. I've not seen anything on the HiRise site to say that their pics are similarly 'falsified', but that intense dark blue could be a slight tinge in reality.

Do you think the blue of the (HiRise) sand dune "blow holes" is too blue to be due to (Mars Rover) blueberries (or some derivative of same)?

by **Dr. Skeptic** » Tue Mar 11, 2008 11:55 am

For the sake of conversation: What if the dark areas were algae?

(Or, dung from giant sand worms?)

by **JohnD** » Sat Mar 08, 2008 11:32 am

neufer,
Note that many Mars Rover pictures are displayed in "false-colour", that exaggerates the colour differences markedly. The eyeball appearance would be a near uniform brown. I've not seen anything on the HiRise site to say that their pics are similarly 'falsified', but that intense dark blue could be a slight tinge in reality.

JOhn

by **neufer** » Sat Mar 08, 2008 2:39 am

Arramon wrote:http://apod.nasa.gov/apod/ap080303.html

So what are those marks that look like impacts? Is that the exploding that happens when the sand thaws?

The process might even involve sandy jets exploding through the thinning ice.

http://www.youtube.com/watch?v=PNm1kfxl ... re=related

<<The blue-tinted colors associated with the scours and ripple crests are probably due to the presence of basaltic sands mixed with hematite-rich spherules.>>
http://marsrovers.jpl.nasa.gov/gallery/ ... 1123a.html
http://www.aapg.org/explorer/2005/05may ... erries.cfm
http://marsrovers.jpl.nasa.gov/gallery/ ... 4R1_br.jpg
http://www.thunderbolts.info/tpod/2004/ ... 27mars.htm
http://www.space.com/scienceastronomy/u ... 40616.html
http://www.space.com/scienceastronomy/h ... 40319.html

by **iamlucky13** » Sat Mar 08, 2008 1:03 am

The CO2 ice doesn't melt into a liquid. It sublimates into a gas...requiring several times it's previous volume and building up pressure.

I suspect the darkness is simply due to the relatively smooth surface being disturbed and broken...more shadowed.

by **JohnD** » Thu Mar 06, 2008 10:48 am

According to the Wikipedia entry on CO2, there IS a glassy version of solid CO2. But it only forms at enormous pressures that need a diamond anvil to acheive! So probably not relevant.

John

by **henk21cm** » Wed Mar 05, 2008 9:50 pm

JohnD wrote: The soil/sand below the water/co2 ice must be dark, very dark if it is the materail thrown upwards by the geysirs. If the ice was transparent,

The ice of carbon dioxide i know is milky white, not as transparent as water ice. Maybe there exists a transparent form of CO2 ice at pressures as low as on Mars. I'm not familiar with that specific transparent form.

JohnD wrote: would sunshine penetrate to the dark soil and heat that, beneath the ice? So the ice began to sublime from the bottom up?

The equilibrium vapour pressure at roughly 150 K is very low. The lowest value i could find is at 175 K ≅ 2 mPa. IMHO too low for a blow out. Effective pressure (of the soil) at 0.2 m below the Martian surface is 0.2 * 3.75 * 1500 ≅ 1 kPa, 6 orders of magnitude larger than the vapour pressure of water at 175 K.

If you replace water by CO2 in your quote, it might work, if there exists a transparent form of CO2 ice. Maybe an idea for a student at a university to experiment with sand, water, CO2 ice and high-power xenon lamps.

Just an amateur,
Henk

by **JohnD** » Wed Mar 05, 2008 9:18 pm

henk,
The soil/sand below the water/co2 ice must be dark, very dark if it is the materail thrown upwards by the geysirs. If the ice was transparent, would sunshine penetrate to the dark soil and heat that, beneath the ice? So the ice began to sublime from the bottom up?

JOhn

by **henk21cm** » Wed Mar 05, 2008 8:44 pm

Arramon wrote:Are there processes on earth that create these similar outward bursts on this same type of frozen dune?

I lack the experience with frozen dunes, the last time i saw frozen dunes, was in 1963, in my childhood. What i can tell from a more recent experience: an odd five years ago experiments were performed by injecting liquid oxygen (90.2 K) into the soil, i.e. silt (d < 63 μm) and aeolian sands. Since the oxygen was injected a depth of a few meters, no blow out occured. Just cracks in the soil. The effective stress in the soil at a depth of 5 m was too high to allow for a blow out.

Thaw of frozen water does not produce an expansion of volume (the opposite occurs): when ice melts, its volume decreases. So water ice can not produce a blow out. Furthermore the change in volume is quite low, 10-15%. Conversely, when liquid oxygen or any other liquid with a low boiling point (below 100K) evapourates, its volume roughly expands by three orders of magnitude: 1 liter of liquid hydrogen produces 800 liters of hydrogen gas.

A proces similar to boiling, can be expected when frozen carbon dioxide (CO2) sublimates into its gaseous phase. When a bubble of gas is created in the soil, at low depth, the effective stress in the soil is too low to prevent a blow out. Cavity expansion theory gives a mathematical treatment of this phenomenon see e.g. http://www.idswater.com/Common/Paper/Pa ... Risk3.htm

As far as i know only the polar regions of Mars are suffciently cold to allow for freezing of CO2. So these sand dunes with a blow out appearence should only occur at high latitudes, if the CO2 explanation is correct. The professional explanation at the apod image speaks of polar region.

Nevertheless there are some points in this explanation which cause trouble.The thermal conductivity of soil is rather low. So when the sun starts heating up the soil, any frozen CO2 at the surface will sublimate rather quickly. Later, solar heat will seep into slightly deeper layers. For a blow out the surface must remain frozen, while the CO2 deeper in the soil must evapourate. This destroyes the explanation with a loud bang.

When temperature drops, of a mixture of water and CO2 gas, the gas with the highest boiling point or freezing point will freeze first, i.e. water. So i expect a layer of water ice to settle on the soil first. Later, when temperature drops further, CO2 ice will settle on top of the water ice. I can not explain why the CO2 ice will freeze at a higher temperature than water ice and so be burried by water ice. So i feel a bit unhappy when reading the professional explanation.

Just an amateur,
Henk

by **Arramon** » Wed Mar 05, 2008 6:28 pm

geonuc wrote:As to the dark material that 'spots' the tops of the dunes, a previous APOD seems to suggest the dune sand itself is dark and what we're seeing is the initial points of thawing at the top of the dunes. Or something like that.

http://apod.nasa.gov/apod/ap040831.html

Those images don't appear the same. The newer one shows only dark spots near the crest of the dune, where it falls to the side blocked by the wind. They look like explosions. Just wondering what chemical reactions cause this besides what the explanation was in the APOD summary. Are there processes on earth that create these similar outward bursts on this same type of frozen dune?

by **bystander** » Wed Mar 05, 2008 1:37 pm

geonuc wrote:As to the dark material that 'spots' the tops of the dunes, a previous APOD seems to suggest the dune sand itself is dark and what we're seeing is the initial points of thawing at the top of the dunes. Or something like that.

Sand Dunes Thawing on Mars (APOD 2008 March 03) suggests the same:

...Thinner regions of ice typically defrost first revealing sand whose darkness soaks in sunlight and accelerates the thaw...

by **geonuc** » Wed Mar 05, 2008 12:56 pm

As to the dark material that 'spots' the tops of the dunes, a previous APOD seems to suggest the dune sand itself is dark and what we're seeing is the initial points of thawing at the top of the dunes. Or something like that.

http://apod.nasa.gov/apod/ap040831.html

by **JohnD** » Wed Mar 05, 2008 7:42 am

neufer,
Certainly one can see where bits of dark material (!) have collected at the bottom of the windward slope (bottom left of above pic) but chevrons I don't see. And I don't think that the wind that formed the dunes is blowing now, as blue is spread against that direction.

My question was more concerned with how this intensely dark pigment is collected together again, recirculated, or else what caused it to be so concentrated under the surface, yet rapidly dispersed above it.

JOhn

by **neufer** » Tue Mar 04, 2008 10:53 pm

JohnD wrote:Where does the black/dark blue material come from, where does it go and how is it re-concentrated under the barchans for the next winter? John

One can guess on where it goes from the picture itself:

The black/dark blue material at the top of the dune is blown down the 34º face making that face black/dark blue (especially at the bottom).

The black/dark blue material columns that used to connect to the top of the dune are left behind as dark chevrons on the windward face.

by **JohnD** » Tue Mar 04, 2008 10:40 pm

Where does the black/dark blue material come from, where does it go and how is it re-concentrated under the barchans for the next winter?

John

by **neufer** » Tue Mar 04, 2008 9:16 pm

Arramon wrote:In other words, don't play on the dunes once we get there. =b

So I guess sandworms are out. O.o
These couldn't be melange spice fields going up? A good spice blow?
hehehe.... no , i guess not.

d'oh! no arrakis for us.

http://en.wikipedia.org/wiki/Arrakis

<<Arrakis, ("the dancer") later Rakis (informally known as Dune) is the third planet orbiting the star Canopus, and it in turn is orbited by two moons. Arrakis is a desert planet with no natural precipitation, and is the only known source of the spice melange, which extends life and makes interstellar travel possible (and is therefore the most essential and valuable commodity in the universe). The planet has no surface water bodies, and giant sandworms (Shai-Hulud) and their immature forms of sandtrout and sandplankton are among the few fauna on the planet. Open canals called qanats are used "for carrying irrigation water under controlled conditions" through the desert. As indicated by large salt flats, Arrakis once had lakes and oceans. "The sandtrout ... was introduced here from some other place. This was a wet planet then. They proliferated beyond the capability of existing ecosystems to deal with them. Sandtrout encysted the available free water, made this a desert planet ... and they did it to survive. In a planet sufficiently dry, they could move to their sandworm phase.">>

http://antwrp.gsfc.nasa.gov/apod/ap070928.html

<<In Dune, the desert of Arrakis is the only known source of the spice melange, the most essential and valuable commodity in the universe. A byproduct of the sandworm life cycle, sandtrout excretions exposed to water become a pre-spice mass, which is then brought to the surface by a buildup of gases and develops into melange through exposure to sun and air. Liet-Kynes describes such a "spice blow" in Dune: "Then he heard the sand rumbling. Every Fremen knew the sound, could distinguish it immediately from the noises of worms or other desert life. Somewhere beneath him, the pre-spice mass had accumulated enough water and organic matter from the little makers, had reached the critical stage of wild growth. A gigantic bubble of carbon dioxide was forming deep in the sand, heaving upward in an enormous "blow" with a dust whirlpool at its center. It would exchange what had been formed deep in the sand for whatever lay on the surface.">>
http://en.wikipedia.org/wiki/Sandworm_(Dune)

by **Arramon** » Tue Mar 04, 2008 6:33 pm

In other words, don't play on the dunes once we get there. =b

So I guess sandworms are out. O.o
These couldn't be melange spice fields going up? A good spice blow?
hehehe.... no , i guess not.

d'oh! no arrakis for us.

Starship Asterisk*

Martian Dunes Thawing (APOD 03 Mar 2008)

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Life on Mars?

Getting the blues

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