APOD: Dark Sand Cascades on Mars (2010 Jan 19)

[APOD Robot]

Dark Sand Cascades on Mars

Explanation: They might look like trees on Mars, but they're not. Groups of dark brown streaks have been photographed by the Mars Reconnaissance Orbiter on melting pinkish sand dunes covered with light frost. The above image was taken in 2008 April near the North Pole of Mars. At that time, dark sand on the interior of Martian sand dunes became more and more visible as the spring Sun melted the lighter carbon dioxide ice. When occurring near the top of a dune, dark sand may cascade down the dune leaving dark surface streaks -- streaks that might appear at first to be trees standing in front of the lighter regions, but cast no shadows. Objects about 25 centimeters across are resolved on this image spanning about one kilometer. Close ups of some parts of this image show billowing plumes indicating that the sand slides were occurring even when the image was being taken.

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[geckzilla]

It should also be noted that the image is in false color. That is, the surface of Mars does not look like this to the human eye. False color was used to bring out details.

What do RED, BG, and IR mean?
These are shorthand titles for the different types of CCDs HiRISE has. The HiRISE camera has three different color filtered CCDs: red ("RED"), blue-green ("BG"), and near-infrared ("IR"). The wavelengths of these filters are as follows: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers

What are the BG and IR EDRs, and How are They Different from RED?
There are ten RED CCDs, two BG CCDs, and two IR CCDs. Combining the images taken by the three different color filters allows us to create "false" color images. The BG and IR CCDs are aligned with the center two RED CCDs, providing a two-CCD-wide color swath. This means that the images captured in the BG and IR products are aligned with the images captured in the RED4 and RED5 CCDs.

What does “false color” Mean?
"False" color means that the color you see in HiRISE images is not the "true" color human eyes would see on Mars. This is because the HiRISE camera views Mars in a different part of the spectrum than human eyes do. Nevertheless, false color imagery is extremely valuable because it illuminates the distinction between different materials and textures.

[metta]

Whow! They sure look like plants to me? If not plants what are they? Thank-you very much for all the daily images. As a senior and as a new student to Astronomy I really enjoy the images very much!

[gravi]

Hi everyone o/
So, they look horizontal lines to me, not vertical ones to be like trees
And about colors, imagine how much amazing scenarios we miss without using the colors filters

[JohnD]

Hey, whoopee! You were as intrigued by that picture as I was!
http://asterisk.apod.com/vie ... 11&t=17958

Thank you for your explanation. You emphasis the false colour - could it be that false or emphasised contrast makes the illusion that the streaks stand up away from the slopes they run down? It is part of sketching technique that drawing a bold, dark stroke makes it appear nearer than a less bold one, improving the '3D' or modelling effect of the drawing.

John

[planetquinn]

If you flip the image 180 degrees it is easier to grasp. The streams then appear to be flowing down instead of up.

[Yeudas]

I don't think that the black sand is the one that felt in cascade.
If you look to this picture of dust evil trails, you can see that actually the black sand appears when the pink and clear sand is removed:

http://apod.nasa.gov/apod/ap091021.html

So the upper level of clear sand should be the one that flowed when ice melted.
How is explained the fact that only a thin layer of light sand covers everywhere the darker level?
Is it a phenomena of oxidization?

[neufer]

Potential Haitian Landslides

Cape Reinga & Te Paki sand dunes

[neufer]

I don't think that the black sand is the one that felt in cascade.
If you look to this picture of dust evil trails, you can see that actually the black sand appears when the pink and clear sand is removed:

http://apod.nasa.gov/apod/ap091021.html

So the upper level of clear sand should be the one that flowed when ice melted.
How is explained the fact that only a thin layer of light sand covers everywhere the darker level?
Is it a phenomena of oxidization?

I would guess that after dust storms the light sand (light in both color & weight)
is the last to "rain out" and physically deposit on an iron heavy hematite surface.

Warm gaseous explosions redeposit the dark hematite onto the surface

<<Hematite is the mineral form of iron(III) oxide (Fe₂O₃), one of several iron oxides. Hematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. It is mined as the main ore of iron. While the forms of hematite vary, they all have a rust-red streak. Hematite is harder than pure iron, but much more brittle.

Huge deposits of hematite are found in banded iron formations. Grey hematite is typically found in places where there has been standing water or mineral hot springs, such as those in Yellowstone National Park in the United States. The mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water, however, usually as the result of volcanic activity. Clay-sized hematite crystals can also occur as a secondary mineral formed by weathering processes in soil, and along with other iron oxides or oxyhydroxides such as goethite, is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils.

The spectral signature of hematite was seen on the planet Mars by the infrared spectrometer on the NASA Mars Global Surveyor ("MGS") and 2001 Mars Odyssey spacecraft in orbit around Mars. The mineral was seen in abundance at two sites on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the second site Aram Chaos near the Valles Marineris. Several other sites also showed hematite, e.g., Aureum Chaos. Because terrestrial hematite is typically a mineral formed in aqueous environments, or by aqueous alteration, this detection was scientifically interesting enough that the second of the two Mars Exploration Rovers was targeted to a site in the Terra Meridiani region designated Meridiani Planum. In-situ investigations by the Opportunity rover showed a significant amount of hematite, much of it in the form of small spherules that were informally named "blueberries" by the science team. Analysis indicates that these spherules are apparently concretions formed from a water solution.>>

<<Heavy mineral sands are a class of ore deposit which is an important source of zirconium, titanium, thorium, tungsten, rare earth elements, the industrial minerals diamond, sapphire, garnet, and occasionally precious metals or gemstones. Heavy mineral sands are placer deposits formed most usually in beach environments by concentration due to the specific gravity of the mineral grains. It is equally likely that some concentrations of heavy minerals exist within streambeds, but most are of a low grade and are relatively small. Specific trap sites for heavy mineral sand placer deposits are in beaches on the leeward side of headlands, as this forms a low-energy zone which traps sediments carried along by the longshore drift. Also, sand bars developed at the mouths of rivers which feed the placer deposits are rich trap sites where the winnowing action of the waves are most efficient, because heavy minerals, if they are going to be too heavy to be moved, will deposit at an isthmus in preference to drifting too far down the beach.>>

[drollere]

visually, probably the ugliest image ever posted on APOD.

[neufer]

visually, probably the ugliest image ever posted on APOD.

But not the most disturbing:
http://antwrp.gsfc.nasa.gov/apod/ap080722.html

[DonAVP]

Reminds me of the fences you see at beaches that keep the sand from blowing away.

I would like to see what this looks like in natural light without any enhancements. It might be kind of boring but would help in understanding the phenoma better.

[neufer]

Reminds me of the fences you see at beaches that keep the sand from blowing away.

• 

<<A sand fence is a structure similar to a Snow fence used to force drifting of sand to occur in a desired place. Sand fences are employed in desert and erosion control and for example to minimize the amount of sand drift on roadways..



The drifting and settling of sand behind and in front of a such a fence occurs because the wind speed on both the downwind and windward side is less than that on the far windward side, allowing light materials such as sand to settle there. This creates a pile both in front of and behind the sand fence causing more sand to drop out. Conveniently the sand does not drop on the barrier itself, otherwise it would soon be buried and rendered useless. Once sand is deposited, it begins to form a self replicating dune.>>

[JohnD]

Right about the fence.
The terrestrial dunes have cascades spaced irregularly along the crest - the Martian ones are extremely regular.

John

[emc]

Earthlings knaw at my gut… I am so sick of their whining and mediocre intelligence. Besides, Earth obscures my view of the Sun. I must destroy it with my super cosmic planet annihilator soon or I shall go mad!

[13 Rabbit]

If you flip the image 180 degrees it is easier to grasp. The streams then appear to be flowing down instead of up.

Way to go! I frequently flip the images. I guess it made for a more exciting photo when viewed up-side down.

[DavidLeodis]

Fascinating image. I think it's . That "Objects about 25 centimeters across are resolved" is amazing (well it is to me!) as that is only about 10 inches.

[Yeudas]

Thank you Neufer for your interesting answer!
Quite puzzling to me too is the fact that the dark sand - outside the cascades - appears in isolated spots, and that those spots seem to be connected to frozen areas. Shouldn't they appear in warmer melting places?

[NoelC]

Cool photo.

One thing always bothers me about Mars... The atmosphere is supposed to be 1% as dense as ours.

How does it suspend so much grit that it has built up huge dunes? Doesn't smell right.

-Noel

[emc]

Sure Mars doesn’t smell right… I mean, it’s full of hostile aliens bent on our annihilation... right? It’s not just the sand dune mystery… Come on, wake up and smell the coffee… Marvin is just a comical diversion! They want our planet… for crying out loud! They’ve seen our TV broadcasts of Baywatch etc. Don’t you get it? Martians cannot be trusted. They hide from our interplanetary probes and telescopes just waiting for the opportunity to strike. Have you not seen Mars Attacks? Those guys in Hollywood… now they know what’s going on… eeek tikkk takk tok! And that’s all she wrote!