Starship Asterisk*

Dry Ice Sled Streaks on Mars

Explanation: What creates these long and nearly straight grooves on Mars? Dubbed linear gullies, they appear on the sides of some sandy slopes during Martian spring, have nearly constant width, extend for as long as two kilometers, and have raised banks along their sides. Unlike most water flows, they do not appear to have areas of dried debris at the downhill end. A leading hypothesis -- actually being tested here on Earth -- is that these linear gullies are caused by chunks of carbon dioxide ice (dry ice) breaking off and sliding down hills while sublimating into gas, eventually completely evaporating into thin air. If true, these natural dry-ice sleds may well provide future adventurers a smooth ride on cushions of escaping carbon dioxide. The above recently-released image was taken in 2006 by the HiRISE camera on board the NASA's Mars Reconnaissance Orbiter currently orbiting Mars.

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Future adventurers...Mars best friend

Who'da thunk those li'l green Martians liked to do ice sledding?

Ann

I thought it was the Spring Olympics...who can go the farthest before their dry ice sled evaporates!!!

Interesting picture, and concept....
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http://apod.nasa.gov/apod/ap120222.html
http://apod.nasa.gov/apod/ap020410.html
. http://asterisk.apod.com/viewtopic.php?f=9&t=27415

The forks in the paths suggest that this is not what is happening - they show no evidence of either side being favoured as would happen if it were blocks sliding down from above.

Cool dry ice sleds; and cool dog! http://farm1.static.flickr.com/82/24972 ... 634ed4.jpg

I have a hard time with the dry ice theory. These streaks remain constant width until the finish line. A ball or chunk of dry ice would sublime as it travels down the slope ... which would cause it to become smaller until vaporized ... which would not cause a constant-width line.

I would like to disagree about the Martian dry ice sled streaks theory. If indeed this is dry ice sublimating as it slid down the slope the trails would become smaller both in width and depth.The picture shows even depth and width of the trenches from top to bottom. mugs

It is not true that the dry ice sublimes into gas as it slides down (well, it does, but only very little), but it only completely sublimes once it comes to a stop at the bottom of the sandy slopes. If you watched the video
the dry ice actually moves very quickly. The APoD description makes it sound as if the sliding is a slow enough process where the effects of sublimation can be seen during the sliding, but this is not true.

Which direction is downhill? I keep changing my mind.

This sure isn't anything like a river. Rivers branch upstream, and grow larger downstream. These tracks both branch and grow (very slightly) to the right. Maybe that implies sublimating, and joining, track-makers moving to the left.

Aw, Shoot. I was hoping those were Sand Worm tracks. (Non-SF fans see Herbert's "Dune")

I think the verb is "sublime" => "subliming". "Sublimate" a noun meaning the product of subliming and recondensing a solid, usually as a means of purification, e.g. "flowers of sulfur" and (some of the) frost inside your freezer. Ya, I know, picky, picky.

Spear Farmer wrote: I think the verb is "sublime" => "subliming". "Sublimate" a noun meaning the product of subliming and recondensing a solid, usually as a means of purification, e.g. "flowers of sulfur" and (some of the) frost inside your freezer. Ya, I know, picky, picky.

From theFreeDictionary online...

sub·li·mate
v. sub·li·mat·ed, sub·li·mat·ing, sub·li·mates
1. Chemistry To cause (a solid or gas) to change state without becoming a liquid.

v.intr. Chemistry
To transform directly from the solid to the gaseous state or from the gaseous to the solid state without becoming a liquid.

Rob

Spear Farmer wrote:I think the verb is "sublime" => "subliming". "Sublimate" a noun meaning the product of subliming and recondensing a solid, usually as a means of purification, e.g. "flowers of sulfur" and (some of the) frost inside your freezer. Ya, I know, picky, picky.

"Sublime" and "sublimate" are synonyms as verbs. While either is perfectly acceptable, I think "sublimate" is the more commonly used form, at least in the astronomical literature I'm familiar with.

mugs wrote:I would like to disagree about the Martian dry ice sled streaks theory. If indeed this is dry ice sublimating as it slid down the slope the trails would become smaller both in width and depth.The picture shows even depth and width of the trenches from top to bottom. mugs

All it takes for this to happen is for the rate of sublimation to be a small ratio to the time it takes for the block to reach its end point.

Marks on Martian Dunes May Be Tracks of Dry-Ice Sleds
NASA | JPL-Caltech | University of Arizona | 2013 Jun 11

Sliding Dry Ice Blocks Make Their Mark on Martian Surface
Planetary Science Institute | 2013 Jun 11

Dry Ice "Snowboards" on Mars
NASA Science News | Dr. Tony Phillips | 2013 Jun 11

Weird Tracks on Mars Could be Caused by Moving Dry Ice
Universe Today | Nancy Atkinson | 2013 Jun 11

BobStein-VisiBone wrote:Which direction is downhill? I keep changing my mind.

This sure isn't anything like a river. Rivers branch upstream, and grow larger downstream. These tracks both branch and grow (very slightly) to the right. Maybe that implies sublimating, and joining, track-makers moving to the left.

It looks to me like the top edge of the dune is toward the upper right hand corner of the image and the gullies run down toward the lower left. Does anyone know for sure?

Anthony Barreiro wrote:

BobStein-VisiBone wrote:Which direction is downhill? I keep changing my mind.

This sure isn't anything like a river. Rivers branch upstream, and grow larger downstream. These tracks both branch and grow (very slightly) to the right. Maybe that implies sublimating, and joining, track-makers moving to the left.

It looks to me like the top edge of the dune is toward the upper right hand corner of the image and the gullies run down toward the lower left. Does anyone know for sure?

That is correct. The tracks run downhill to the lower left and end abruptly, sometimes with little pits at the end (presumably where the remaining sled sublimated away). I assume most are about the same length because at that distance from their start the surface has leveled out enough that they get snagged in the sand and stop sliding.

Hey! You stole my idea!
I posted this on Cosmoquest on the 13th!

"A paper in the journal Icarus has proposed a "Hypothesis for the formation of martian linear gullies"
http://www.sciencedirect.com/science/ar ... 3513001668

The authors suggest that blocks of the seasonal Polar icecap, made mainly of solid CO2, break off in Spring and slide down the slope below the cap, the friction lessened by fine sand and by a layer of subliming gas under the block. The sliding blocks may leave the 'linear gullies' that have been noted on Mars since close up pictures were first available, but for which there was no explanation.

So far, so scientific. But, Ba Roos, Man! This is dune boarding to the Max! First dude to hang a toe is the Champ!

When, not if, we live there, this has to be a new 'extreme' sport.
How big an ice block would be needed to ride it?"

I later estimated that, as the VP of solid CO2 at -70C is between 1000 and 1500mmHg, any block big enough to stand on would do.
In other words body-board sized piece would let you surf the Martian sands.


John

A little poking around through the links in the caption reveals that this photo is of an area in Russell Crater in Mars' southern hemisphere. The crater was named after the American astronomer Henry Norris Russell, half of the namesake of our beloved Hertzsprung-Russell diagram.

My observation of this is.....this is over many, many, many, generations of this going on, probably even billions of years, a little bit more each time,....not just a one time seasonal thing and it is gone....some people might describe it as water flow...
http://www.godandscience.org/images/uni ... esmars.jpg

These are deep "canyons" that wend down the sides. There are "paths of least resistance". There are many different starting points that meld into the other channels. This could be mistaken as water erosion, it is very similar. Maybe less debris at the bottom, but still....I wonder if Ancient Water contributed to the channels.
There is a phenomena in deserts where rocks move on flat ground...it is the wind and the wetness. And they leave tracks that go for quite a ways.

It is not so much "Snowboarding", as it is "THE LUGE".....

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A deluge of sliding sublimation.

I don't think the dry ice theory fits ... the "linear gullies" would get narrower toward the bottom of the mound as the ice sublimes.

My Theory: These are stretch marks. The mounds were once relatively flat, but molten sulfer flowed out of the ground (smoothly, not in an explosion) a long time ago. Before the sulfer cooled (eons ago) water (maybe from the sky ... maybe from a flood) flowed over it, creating an elastic anhydrous sulfer compound/mix. This reaction may also have effectively covered the hole so the hot sulfer ceased to flow (temporarily); because, before it crystalized, pressure from below increased the size of the mound beyond the stretch limits of the elastic covering, causing something similar to the stretch marks we see on human skin when internal pressure separates the outer skin. Since it seems unlikely that the sulfer would just stop flowing at this point, there may be a (cooled) flow on one of the other sides of the mound. One way to test this theory is to look for change over a few years. If the "linear gullies" change year-by-year, then the theory probably doesn't "hold water." ('scuse the pun)

JML-Virginia wrote:
I don't think the dry ice theory fits ... the "linear gullies" would get narrower toward the bottom of the mound as the ice sublimes.

Place an ice cube from the fridge in the center a frying pan and set on a heat setting of your choice.

Does the ice cube (basically) maintain it's width as it shrinks in height?

I recommend frying a square of butter instead. Then you can beat some eggs and throw them on top once the butter melts and have a nice meal.