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APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 10:17 am
by 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.
[/b]
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 10:18 am
by RJN
Today's APOD was late in appearing due to (my own) human error. My apologies. - RJN
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 11:49 am
by BikerMike
Better late than never!
![Wink :wink:](./images/smilies/icon_wink.gif)
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 12:42 pm
by orin stepanek
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 1:02 pm
by 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!
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 1:10 pm
by 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
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 1:58 pm
by orin stepanek
owlice wrote: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.
![Shocked :shock:](./images/smilies/icon_eek.gif)
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 2:21 pm
by neufer
http://en.wikipedia.org/wiki/Namib_Desert wrote:
<<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.>>
http://en.wikipedia.org/wiki/Sossusvlei wrote:
<<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.>>
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 3:14 pm
by bystander
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 4:30 pm
by neufer
Titan's slow earthwise rotational period: 15.945 earth days
Does Titan have an anti-Hadley cell circulation during equinox?
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 5:22 pm
by 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.
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 6:28 pm
by neufer
biddie67 wrote: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.
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.
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 7:32 pm
by 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?
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Tue Aug 10, 2010 7:53 pm
by bystander
Bruce McCurdy wrote: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?
Release the Kraken Mare!
Posted: Tue Aug 10, 2010 9:31 pm
by neufer
http://en.wikipedia.org/wiki/Titan_%28moon%29 wrote:
<<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.>>
Re: APOD: The Sand Dunes of Titan (2010 Aug 10)
Posted: Wed Aug 11, 2010 3:10 pm
by hess
Anyone notice the clouds(water?) and their shadow in the lower right hand corner?