APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

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Expand view Topic review: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by neufer » Sat Jan 18, 2014 8:29 pm

http://www.planetary.org/blogs/guest-blogs/2014/20140116-dry-ice-snowfall-at-the-poles-of-mars.html wrote:
Dry Ice Snowfall at the Poles of Mars
Posted by Paul Hayne, Planetary Society, 2014/01/16

<<Let's take a closer look at [Martian] polar caps. With a large enough telescope, you can observe their seasonal growth and retreat, just as scientists did in the late 19th century. By analogy with Earth, they were first presumed to be composed of water ice, until a pair of researchers at Caltech in the 1960s showed that winter temperatures should drop to a bitter –125°C. At that point, the Martian atmosphere itself (composed primarily of carbon dioxide, CO2) should begin to freeze out. Thus, the seasonal ice caps of Mars ought to be composed primarily of CO2, rather than water ice. Given that no spacecraft had ventured beyond Earth orbit at the time, Robert Leighton and Bruce Murray's model was surprisingly accurate, and many of their predictions were borne out by planetary spacecraft observations in the following decade.
[img3="What does a Martian snowflake look like?
As seen by Earth-based experimenters, carbon dioxide crystals
have a "cuboctahedral" shape – cubes with the corners cut off.
These particles are much smaller (~100x smaller) than terrestrial
water snow, and lack their intricate symmetry & platy structure.
"]http://planetary.s3.amazonaws.com/asset ... 4_f537.jpg[/img3]
One of the most striking predictions of the Leighton and Murray (LM) model was that over the Martian seasons the mass of the atmosphere should vary by ~30% as CO2 is exchanged with the polar caps. LM therefore showed that this atmospheric freeze-out should be expressed in pressure readings taken anywhere on the planet. When the Viking landers touched down in 1976, it had been ten years since LM’s publication. As the pressure data came in, the telltale signature of the Martian global CO2 cycle showed up clear as day.

As more advanced spacecraft have explored Mars, our understanding of the polar caps has improved, yet new data continue to reveal complex and sometimes baffling processes. We now know that underneath the seasonal CO2 caps are massive layered deposits of water ice (enough water to flood the planet 10 meters deep), which are probably vestiges of a warmer, wetter Mars. Only the south pole harbors a permanent CO2 deposit, and until recently it was thought to be a minuscule mass in comparison with the seasonal deposits. However, data from the SHARAD radar system on the Mars Reconnaissance Orbiter (MRO) revealed in 2011 that this dry ice deposit extends up to a kilometer deep, and may be enough to double the present Martian atmosphere.

How did this massive CO2 deposit get there? Does its presence imply the atmosphere of Mars is collapsing over multi-year time scales? To the contrary, some researchers think the CO2 deposit is unstable, and may be returning to the atmosphere. They cite evidence from high resolution images taken several Mars years apart, which show the growth of "Swiss cheese" pits in the CO2 ice. Yet other observations and models suggest the cap is in a state of tenuous, but stable equilibrium. A key to settling this debate lies in the balance of energy sources and sinks in the polar regions. Chief among these are solar and infrared radiation, which compete over the energy stored as latent heat in solid CO2. In the polar winter, as on Earth, the sun is below the horizon throughout the day. Under these conditions, the infrared emission to space has little competition, and carbon dioxide condenses out of the atmosphere at a rapid rate. While the basics of this condensation process are understood, the darkness of polar night has veiled important details. Where and when does CO2 condensation occur? How rapidly is the atmosphere depleted? Does it snow?

As a resident polar scientist on the Mars Climate Sounder (MCS) science team, I led a series of two studies to investigate the possibility of CO2 snowfall and its consequences for the Martian climate. We focused on the south pole, where viewing conditions are more favorable, and the perennial CO2 cap is located. MCS has the advantage of being able to "see in the dark" with its infrared detectors, and also has its own actuators to allow scanning between the surface and atmosphere. In the first study, published in 2012 in the Journal of Geophysical Research, we used MCS infrared measurements to show that CO2 snow clouds were in fact prevalent in regions of active polar cap growth. More than that, these clouds and snow particles were blanketing the surface by blocking infrared radiation, which strongly affects the polar energy balance. For this reason, CO2 snow clouds are important drivers of the Martian climate.

In the second study, just out in the journal Icarus, we looked at the CO2 clouds in more detail in order to estimate the rate of snowfall. Theoretical models had predicted a range from near zero, up to about 40% of the seasonal caps might be made of snow, rather than frost. We used two independent methods to test the theory. First, by retrieving vertical profiles of temperature, pressure, and CO2 ice particle concentration from the MCS data, we used models to calculate the energy budget at every level in the atmosphere and on the surface. Balancing the rate of energy loss with that released by the latent heat of CO2 deposition gives a range of 3–20% of precipitation occurring as snowfall. The second approach involved the gravitational settling of snow particles. By looking at differences in the infrared brightness of the cloud in MCS's different wavelength channels we were able to constrain the particle sizes (10 – 100 μm), which can then be fed into a model for their rate of descent through the atmosphere. This approach gave a snowfall contribution of 7–15%. With good agreement between the two approaches, we can be confident in our results. These new observations help us understand the process and the role of CO2 snowfall in forming the seasonal ice caps of Mars, and will help Mars climate scientists improve their models.

Skiing or snowboarding on Mars could be attempted on either the CO2 part of the ice cap, or the water ice part. Evidence suggests the water ice part of the cap is very ancient, and is therefore probably very dense; ice skating would be a better fit. On the fresh seasonal CO2 cap, with up to 20% made of fluffy snow, skiing might be possible. At about 1/3 the surface gravity of Earth, it would take longer to achieve a given speed on a slope, although air resistance would be negligible. "Getting air" would be much easier in the reduced gravity, so I would recommend installing a half-pipe for some insane aerials. A significant unknown is how skis or boards would perform on dry ice. Unlike on terrestrial snow, which is slippery because it typically has a thin melt layer surrounding the grains, carbon dioxide is truly "dry ice." When heated (by friction, for instance), it will sublimate straight to the gas phase. If the friction beneath a ski is too great, this could generate a layer of air, causing a total loss of control. Finally, because the CO2 snowfall occurs almost exclusively in the polar night, you had better bring your night-vision goggles.>>

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by geckzilla » Tue Jun 18, 2013 3:00 pm

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.

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by neufer » Tue Jun 18, 2013 12:13 pm

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?

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by JL-Virginia » Tue Jun 18, 2013 11:43 am

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)

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by Beyond » Tue Jun 18, 2013 1:36 am

A deluge of sliding sublimation. 8-)

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by Boomer12k » Tue Jun 18, 2013 1:29 am

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"..... :)

:---[===] *

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by Anthony Barreiro » Mon Jun 17, 2013 8:36 pm

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.

Image

Image

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by JohnD » Mon Jun 17, 2013 5:50 pm

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

Re: Downhill to the left?

by Chris Peterson » Mon Jun 17, 2013 5:40 pm

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.

Re: Downhill to the left?

by Anthony Barreiro » Mon Jun 17, 2013 5:31 pm

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?

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by bystander » Mon Jun 17, 2013 3:02 pm

Yoduh wrote:
Click to play embedded YouTube video.
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

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by geckzilla » Mon Jun 17, 2013 2:59 pm

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.

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by Chris Peterson » Mon Jun 17, 2013 1:40 pm

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.

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by rstevenson » Mon Jun 17, 2013 1:32 pm

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

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by Spear Farmer » Mon Jun 17, 2013 1:26 pm

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.

Downhill to the left?

by BobStein-VisiBone » Mon Jun 17, 2013 12:38 pm

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.

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by Yoduh » Mon Jun 17, 2013 12:29 pm

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
Click to play embedded YouTube 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.

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by mugs » Mon Jun 17, 2013 12:00 pm

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

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by JL-Virginia » Mon Jun 17, 2013 11:39 am

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.

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by orin stepanek » Mon Jun 17, 2013 11:38 am

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by madtom1999 » Mon Jun 17, 2013 7:40 am

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.

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by neufer » Mon Jun 17, 2013 6:10 am

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by Boomer12k » Mon Jun 17, 2013 5:18 am

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

Interesting picture, and concept....
:---[===] *

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by Ann » Mon Jun 17, 2013 4:46 am

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

Ann

Re: APOD: Dry Ice Sled Streaks on Mars (2013 Jun 17)

by Beyond » Mon Jun 17, 2013 4:17 am

Future adventurers...Mars best friend :?: :lol2:

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