[X] My Assistant

[volcanopele]

Well, for those who really like RADAR SAR swaths, today is a good day for you. The T13 RADAR swath from April, THE ENTIRE SWATH, has been publically released on the Photojournal.

Titan (T13) Viewed by Cassini's Radar - April 30, 2006
http://photojournal.jpl.nasa.gov/catalog/PIA08552

PIA08604: Xanadu's Meandering Rivers
http://photojournal.jpl.nasa.gov/catalog/PIA08604

PIA08605: Titan's Geological Goldmine - Radar Movie
http://photojournal.jpl.nasa.gov/catalog/PIA08605

[elakdawalla]

Wow! Thanks for the heads up!

They're slightly vague about the scale, would you be able to tell more exactly -- is this at 128 pix/degree? That would be closest to the "smallest details in this image are about 400 meters across" -- or is it actually 400 m/pixel?

--Emily

[volcanopele]

The pixel scale is approximately 234 m/pixel.

[volcanopele]

A few comments on some of the amazing features seen in this swath (my favorite thus far) as well as a comment on the movie.

First, regarding the movie: in the movie, they highlight a few of the intriguing features seen in the swath, particularly the Xanadu east and west "coasts". While these may be the margins in RADAR, they are not the margins at IR wavelengths. The west margin basically matches, though the upper portion of the margin in the swath does not match. Part of the IR-bright Xanadu terrain appears dark. The eastern margin doesn't match AT ALL. The IR margin is actually beyond the eastern end of the swath. There are no IR traces of the RADAR margin on the eastern side. Again, the one constant of broad IR dark terrain (not the small patches, which can appear hilly, smooth, rough, etc. in RADAR) is that they are covered in longitudinal dunes.

Now on to the swath itself (for the rest of this discussion, note that RADAR illumination is from above). One thing I love about this swath is that it has "real" topography. Sure, the others did as well, but this one has honest to goodness plateaus, and other really cool geomorphology. In this first image, below, you see some plateaus just east of the river systems in western Xanadu. The most prominent plateaus is along the top of the swath on the right side of this cutout. What is neat is that you can see several streams starting out at the bottoms of canyons along the plateau margin. You can also see this at a smooth topped plateau to the southwest. Throughout this area, you can see plateaus with canyons along their margin, which suggest that methane can erode into the surface and these rivers can form in much the same way that river do on earth.



In this next cutout, we see a patch of hills at the eastern end of the RADAR swath. This isolated hills are located within an area of smooth, bright terrain in eastern Xanadu. Emanating from the hills are three radiating channels (though the ones to the west and south may be the same channel diverting around the patch of hills.



This swath also appears to have a number of apparent impact craters. The third image below shows a few of them, though it can't be ruled out that some or all of these are actually cryovolcanoes. This view also reveals the smallest impact crater revealed thus far at around 15 km across (the bottom left one). The bottom right crateriform is Guabonito. The top right has an apparent central peak, but the extension of smooth material from its southwestern margin has led to the suggestion that it might be a cryovolcano. the crateriform at top right may be a viscously relaxed crater where only its rim is still visible.

[Guest_AlexBlackwell_*]

A few comments on some of the amazing features seen in this swath (my favorite thus far) as well as a comment on the movie.

Thanks, Jason. Interesting.

[Malmer]

is there a composite with all radar swaths so far?

[Guest_paulanderson_*]

Cassini Reveals Titan's Xanadu Region To Be an Earth-like Land
http://saturn.jpl.nasa.gov/news/press-rele....cfm?newsID=675

[tty]

This swath also appears to have a number of apparent impact craters. The third image below shows a few of them, though it can't be ruled out that some or all of these are actually cryovolcanoes. This view also reveals the smallest impact crater revealed thus far at around 15 km across (the bottom left one). The bottom right crateriform is Guabonito. The top right has an apparent central peak, but the extension of smooth material from its southwestern margin has led to the suggestion that it might be a cryovolcano. the crateriform at top right may be a viscously relaxed crater where only its rim is still visible.

I don't see that that extension would invalidate an impact origin. We know from terran impact craters that a lot of heat remains in the ground for a long time after the impact. Geothermal effects last for millenia and in the Sudbury structure in Canada the crater seems to have been filled by a lava pool for quite some time. It seems quite reasonable that there might be a lot of secondary melting and flooding after a large Titanian impact. This might also explain that the Titanian impact structures are so subdued, large impacts may be self-destroying.

tty

[Big_Gazza]

Wow... Two complete SAR swaths within the space of a week or so... Life is good.

Not wanting to be thought of as an ingrate, I have to wonder why T13 was released so soon? T7 over Mezzoramia took a whole year to come out, and now T13 is out before the lid has been lifted on T8 over Belet/Adiri?

Maybe NASA is planning to thrice bless the faithful with T8 release soon? Please?

[The Messenger]

Wow... Two complete SAR swaths within the space of a week or so... Life is good.

Not wanting to be thought of as an ingrate, I have to wonder why T13 was released so soon? T7 over Mezzoramia took a whole year to come out, and now T13 is out before the lid has been lifted on T8 over Belet/Adiri?

Maybe NASA is planning to thrice bless the faithful with T8 release soon? Please?

It depends upon how much evidence of civilization they have to scrub out of the swaths before posting - part of the prime directive you know, not to antagonize the natives

Seriously, no complaints about how quickly the radar images are being released. I can understand why mission scientists would like more time to ponder what they are trying to interpret.

[Guest_AlexBlackwell_*]

Read Emily's interpretation.

[elakdawalla]

The pixel scale is approximately 234 m/pixel.

...which worked out to just about exactly 192 pixels/degree (i.e. 1.5 * 128), a number that made sense. Thanks, Jason. --Emily

[Guest_AlexBlackwell_*]

Lunine waxes poetic:

"Although Titan gets far less sunlight and is much smaller and colder than Earth, Xanadu is no longer just a mere bright spot, but a land where rivers flow down to a sunless sea," Lunine said.

[elakdawalla]

Indeed. Here's the source of the poetry, for those who've forgotten their Coleridge. I like the fact that this poem has already been the source of a lunar geologic term.

In Xanadu did Kubla Khan
A stately pleasure-dome decree :
Where Alph, the sacred river, ran
Through caverns measureless to man
Down to a sunless sea.

So twice five miles of fertile ground
With walls and towers were girdled round :
And there were gardens bright with sinuous rills,
Where blossomed many an incense-bearing tree ;
And here were forests ancient as the hills,
Enfolding sunny spots of greenery.

....

[Guest_AlexBlackwell_*]

Indeed. Here's the source of the poetry, for those who've forgotten their Coleridge.

The well-known phrase "down to a sunless sea" has been used, for example, as the title for a couple of books, including one of my favorites by David Poyer.

I like the fact that this poem has already been the source of a lunar geologic term.

Careful, Emily, some of the nutcases may think you're referring to "dome[s]" and "walls and towers."

Seriously, though, does anyone (Phil Stooke?) happen to know why "rille" was used for the lunar trenches/valleys even though "rill" is listed as an alternate spelling in Webster's? I suspect that is was because "rill" is also used to denote "a little brook or rivulet" but I'm just guessing. BTW, the word is of Germanic origin.

This post has been edited by AlexBlackwell: Jul 21 2006, 01:42 AM