[X] My Assistant

[volcanopele]

The latest issue of Science has hit the web, and it contains an article by Lorenz et al. on the Great dune seas of Titan, as seen in T8 RADAR data:

http://www.sciencemag.org/cgi/content/abstract/312/5774/724

The article characterizes the longitundinal dunes seen in the equatorial dark regions and compares them to those seen in the Namib desert in southwestern Africa.

[Guest_paulanderson_*]

Good article here, also:

Titan's Seas Are Sand
http://uanews.org/cgi-bin/WebObjects/UANew...ArticleID=12614

[Guest_paulanderson_*]

Colossal Dunes Swathe Saturn's Giant Moon
http://www.newscientistspace.com/article/d...giant-moon.html

Saharan Sand Dunes Found on Saturn's Moon Titan
http://space.com/scienceastronomy/060504_sands_titan.html

Titan Dunes
http://www.nasa.gov/mission_pages/cassini/...s-20060505.html

[David]

Is there an estimate of what the average distance, crest to crest or trough to trough, of the dunes might be?

[volcanopele]

According to the article, the dunes are spaced about 1-2 km apart. A graph in the article shows that the crest to crest spacing is about 2-3 km in southwestern Belet.

[Thorsten]

So, longitudinal (seif) dunes on Titan are 100 – 150 m high and hundreds or thousands of km long with slopes of 6 – 10% and an average space from crest to crest of 2 – 3 km. Variable eastwards flowing surface winds of 0.5 km/s produce these dunes of 0.1 - 0.3 mm sized sand particles (slightly larger grain size than on Earth). Note that the image below shows a 5x vertical exaggeration.

For what its worth (probably it’s worth nothing at all), nomads of the Sahara desert – which have acquired an extensive vocabulary of sand dunes – call the crests of large longitudinal dunes Shnûf, while a large interspace between two dunes is called Aftût (a small one is called Gûwd) and a large longitudinal dune without crest is called Elb. Might be useful for future Titan explorers .

BTW, somebody wrote already an article about the sand dunes of Titan in the Wikipedia (Titan). Great work!

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[volcanopele]

I've moved the off-topic Huygens related discussion to a more appropriate thread:

http://www.unmannedspaceflight.com/index.php?showtopic=2704

[Guest_paulanderson_*]

I've moved the off-topic Huygens related discussion to a more appropriate thread:

http://www.unmannedspaceflight.com/index.php?showtopic=2704

Thanks. So does anyone else have input regarding these huge, wide-spread dunes? I thought there'd be more discussion about them? A remarkable find I think.

[helvick]

Thanks. So does anyone else have input regarding these huge, wide-spread dunes? I thought there'd be more discussion about them? A remarkable find I think.

Absolutely remarkable but the discussions here had gone into the dynamics of such dune formations at length over the past 12 months at least. When I saw these I immediately thought of the Namid desert - I've flown over it by day a good few times and much of it is covered by immense seif dune fields. Funny thing is that I just searched the web for "Namib desert longitudinal dunes" and got this link for a Cassini LPSC paper as the first hit. When you see the Namib from the air you really begin to understand the meaning of the words magnificent desolation.

[volcanopele]

A giant chunk of the T8 RADAR SAR swath has been released on the planetary photojournal: http://photojournal.jpl.nasa.gov/catalog/PIA08454 . This is the largest contingous chunk of SAR swath ever released, AFAIK. This portion covers the dark region known as Belet. This dark region is covered in longitundinal sand dunes with the occasional hilly splotch to divert the dunes. On the right side of the swath is the western portion of Adiri.

[David]

A giant chunk of the T8 RADAR SAR swath has been released on the planetary photojournal: http://photojournal.jpl.nasa.gov/catalog/PIA08454 . This is the largest contingous chunk of SAR swath ever released, AFAIK. This portion covers the dark region known as Belet. This dark region is covered in longitundinal sand dunes with the occasional hilly splotch to divert the dunes. On the right side of the swath is the western portion of Adiri.

It reminds me of a Zen rock garden, the sand neatly raked in symmetrical rows, every once in a while broken by an irregular rock that the rows have to divert around.

It seems that Titan has both "wet" and "dry" zones -- the former being where we have extensive channelling (and so presumably either upwelling or downpour of liquids) -- and the latter being the dunes and other terrain lacking channels.

I note on the extreme right of this swath what looks to me like extensive cratering -- extensive for Titan, that is. I believe I also see traces of cratering in the Dune Sea at the left end of the swath, lighter colored rings or arcs. But the dunes cut right through them, suggesting to me that the craters are pretty much covered over -- probably invisible from the surface -- and that the dune-formation processes have been active in the relatively recent past. For the most part the Dune Sea shows no cratering at all.

My question is whether we know enough, yet, about the distribution of the wet and dry zones to form a hypothesis about why they are where they are? Obviously, much of the equatorial region is "dry", and yet Huygens found extensive small-scale channeling going on even there.