APOD: The Sand Dunes of Titan (2010 Aug 10)

[APOD Robot]

The Sand Dunes of Titan

Explanation: Why do some sand dunes on Titan appear backwards? Central Titan, it turns out, is covered by sand, some of which appears strange. Images from the Cassini spacecraft currently orbiting Saturn have uncovered long rows of huge sand dunes near Titan's equator that rise as high as 300 meters. Shadows indicate that most dune shapes are created by wind blowing from the west. The problem is, the typical wind at Titan's equator blows from the east. One recent hypothesis that might solve this grainy conundrum posits that the only winds strong enough to move sand and create dunes occur during rare equinoxes and blow strongly from the west. The above images show a radar swath of Titan's equatorial sand dunes at the top, while similar sand dunes that formed in Namibia on Earth at the bottom. Why central Titan is even covered by so much sand is still being investigated.

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[RJN]

Today's APOD was late in appearing due to (my own) human error. My apologies. - RJN

[BikerMike]

Better late than never!

[orin stepanek]

A litttle something from today's APOD! http://www.youtube.com/watch?v=f_ybMvQZBMI

[owlice]

Orin, wasn't that something?!! And as it starts to go over, the brake lights come on...! A natural reaction, I suppose, though a fruitless one in this case!

[mexhunter]

Usually I see it at 11:01 pm (local time in Mexico), so for me is almost always yesterday's APOD.
As Terminator said: "No Problemo".
Regards
Cesar

[orin stepanek]

Orin, wasn't that something?!! And as it starts to go over, the brake lights come on...! A natural reaction, I suppose, though a fruitless one in this case!

I saw one go over on a TV show one time! It was very similar to this one; but in a different location. I think it was on one of the shows that show police chases. It would be pretty scary to see one go over while driving.

[neufer]

The crests of the Namib dunes are aligned in a marked NW-SE orientation. The dunes cause the southerly winds to be deflected significantly to the right into a southwesterly wind.

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<<Having endured arid or semi-arid conditions for at least 55 million years, the Namib Desert is considered to be the oldest desert in the world. The name "Namib" is of Nama origin and means vast. The Namib's aridity is caused by the descent of dry air of the Hadley Cell, cooled by the cold Benguela current along the coast. It has less than 10 mm of rain annually and is almost completely barren. A huge group of sand dunes, which at more than 300 meters high are among the tallest sand dunes in the world. The complexity and regularity of dune patterns in its dune sea have attracted the attention of geologists for decades. They still remain poorly understood.>>

<<Sossusvlei is a clay pan in the central Namib Desert, lying within the Namib-Naukluft National Park, Namibia. Fed by the Tsauchab River, it is known for the high, red sand dunes which surround it forming a major sand sea. Vegetation, such as the camelthorn tree, is watered by infrequent floods of the Tsauchab River, which slowly soak into the underlying clay.>>

Sossusvlei dry

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Sossusvlei partially flooded

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[bystander]

Communications: Blowing in the Wind

[neufer]

Communications: Blowing in the Wind

Titan's slow earthwise rotational period: 15.945 earth days
Does Titan have an anti-Hadley cell circulation during equinox?

[size=175][color=#00BF00]Hadley cell Equatorial Easterlies on Earth[/color][/size]

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[biddie67]

I have been known to complain some that I can't see much of the night time sky because of all the trees here. BUT after seeing pictures of the Namib Desert sure makes me appreciate those trees - I'll have to go outside tonight and hug a few of them!!

Having been in Belize on the coast, I can appreciate the steadiness of the Trade Winds coming off the ocean. On the rare occasions that it stops blowing, the insects swarm out of the jungle and one must stay inside, imprisoned behind sturdy screens. But there wasn't any obvious evidence that the wind changed directions and started blowing from the west.
With Titon revolving so slowly, it's hard to see how the winds could change direction and strength enough to create the strange sand dune patterns even with the extra (minor?) heat input from an equinox.

[neufer]

With Titon revolving so slowly, it's hard to see how the winds could change direction and strength enough to create the strange sand dune patterns even with the extra (minor?) heat input from an equinox.

The Intertropical Convergence Zone (ITCZ)

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I'm just guessing here but:

On Earth the equatorial center of the Hadley circulation's easterly winds is the Intertropical Convergence Zone (ITCZ) which tracks the sun north & south over the year.

However, during the equinox time period it is not unusual for the ITCZ to BIFURCATE into a DOUBLE ITCZ (one on either side of the equator). This might allow for westerly winds over the equator during equinox time period and it might also emulate what happens on Titan.

[Bruce McCurdy]

In the Namibia half of the APOD the white splotches are clearly clouds, as they have analog shadows on the ground (the dark splotches). Are the white splotches on the Titan half of the APOD also clouds in its atmosphere? Or some sort of surface feature?

[bystander]

In the Namibia half of the APOD the white splotches are clearly clouds, as they have analog shadows on the ground (the dark splotches). Are the white splotches on the Titan half of the APOD also clouds in its atmosphere? Or some sort of surface feature?

The bright features (top) are not clouds but topographic features.

[neufer]

Composite map of Titan's surface.

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<<The surface of Titan has been described as "complex, fluid-processed, [and] geologically young". The Cassini spacecraft has used radar altimetry and synthetic aperture radar (SAR) imaging to map portions of Titan during its close fly-bys of the moon. The first images revealed a diverse geology, with both rough and smooth areas. There are features that seem volcanic in origin, which probably disgorge water mixed with ammonia. There are also streaky features, some of them hundreds of kilometers in length, that appear to be caused by windblown particles. Examination has also shown the surface to be relatively smooth; the few objects that seem to be impact craters appeared to have been filled in, perhaps by raining hydrocarbons or volcanoes. Radar altimetry suggests height variation is low, typically no more than 150 meters. Occasional elevation changes of 500 meters have been discovered and Titan has mountains that sometimes reach several hundred meters to more than 1 kilometer in height. Titan's surface is marked by broad regions of bright and dark terrain. These include Xanadu, a large, reflective equatorial area about the size of Australia. The convoluted region is filled with hills and cut by valleys and chasms. It is criss-crossed in places by dark lineaments—sinuous topographical features resembling ridges or crevices. These may represent tectonic activity, which would indicate that Xanadu is geologically young. Alternatively, the lineaments may be liquid-formed channels, suggesting old terrain that has been cut through by stream systems.>>

[hess]

Anyone notice the clouds(water?) and their shadow in the lower right hand corner?