Titan's topography, strange.... Options

[dvandorn]

I will point out that, on the Moon, the highland uplands correspond to the less dense (and therefore lower gravitational potential) areas of the lunar gravisphere, while the mare lowlands correspond to the more dense (and therefore higher gravitational potential) areas -- the mass concentrations, or mascons.

In the case of the Moon, the lighter material (mostly anorthositic melt) rose to the top of the crust. Denser mare lavas extruded later occupied the lower reaches, especially within the confines of large impact basins.

Just because a piece of the crust is pushed up, or is on top of the general mean level of the crust, doesn't necessarily mean (as it usually does on Earth) that there is a massive pile of dense rock forming the mountains or the uplands, with deep "roots" into the crust. As in the case of our Moon, sometimes the uplands and mountain ranges are higher because they are less dense and rose to the surface of a molten crust.

In the case of Titan, maybe the entire crust was once molten (i.e., in the liquid phases of its constituents) and the mountains and other highlands are just places where the lighter materials floated to the top? Denser materials may have since occupied the lowlands, creating what appears to be low-density windows in the crust where the lighter materials haven't been sunk under more dense stuff that was either extruded from below or rained down from above?

-the other Doug

[titanicrivers]

Sorry to change the subject a bit but it’s Sunday and time for a “Hot Cross Bun”! Titan’s T83 possible volcanic or diapiric construct is heavily ‘denoised’ and contrasted and 3D’d (Todd Wildrick’s T3D- 2d to 3d image converter). I haven’t yet seen detailed topography for this portion of T83 so the vertical profile of the image below may be exaggerated or even reversed.

[dilo]

titanicrivers, I have impression that depth in this stereogram is solely related to local luminosity... did you used real topography info or is T3D program simply using a pseudo elevation map based on the albedo image processed by you?

[titanicrivers]

... did you used real topography info or is T3D program simply using a pseudo elevation map based on the albedo image processed by you?

Keen observation dilo. I did not have stereographic images, just the T83 SAR image that was denoised and contrasted. The T3D program produces its own stereo image from your original and one can manipulate the images to reverse height/depth cues and adjust the degree of depth/height. I tend to use it on images where reasonable assumptions can be made as to the nature of the topography and I choose conservative values. The effect is more for its 'artistic' rather than 'accurate' view of the image. I think it did an fine job on that T39 river emptying into Mezzoramia Basin.

[TheAnt]

Actually, Ant, the lower than expected local gravity over these mountains implies that there is less mass beneath them than would be expected on a terrestrial world. This is surprising and unexpected.
Hmm. "Surprising and unexpected" may be a serviceable blanket description of Titan all by itself. Fascinatingly different in almost every possible respect.

You are right, I did speculate a bit with the fact that ice is somewhat less dense than water. But also have to admit that I am grasping at straws here trying to comprehend this aspect of Titan. It is a fascinating world indeed.

And dvandorn found one example to erode my line of thinking even further. That the highlands might be piles of material on a rather rigid crust. I go with that idea for the time being, now that water ice will indeed be very hard in the temperature range we got on Titan.

[titanicrivers]

Another interesting Titan-Earth comparison involves the T83 swath. Is there diapirism on Titan analagous to the laccoliiths (diapirs) on earth in Utah (Henry mountains).

[stevesliva]

That aerial view of the Henrys makes them look more rugged than they actually are. Long shadows.

I also wonder whether the "diaper" on titan is actually a massif... any topography info on that scale? Could just be a low-relief area of fractured terrain.

[titanicrivers]

You have excellent points there stevesilva but I don’t have good answers. I do show below Titan and the Henry’s to scale and Its apparent Titan’s constructs are much larger. I haven’t seen topographic data that would begin to answer your concerns about Titan’s “wrinkles”. My assumption is that there is some elevation and erosion involved in their formation.

[stevesliva]

I was wondering about the scale, too. In your image... hot crossed bun upper left?

Yes, with the huge scale of relatively chaotic terrain-- it doesn't make me think of mountain ranges on earth, at least not those in the I do think that Titan has crazy faulting from diapirism, I just don't want to say it has a peak or ridge or range. I envision it being flatter and more chaotic.

[titanicrivers]

I was wondering about the scale, too. In your image... hot crossed bun upper left?

Yup! The scale marker is from this image on NASA's Photojournal page http://photojournal.jpl.nasa.gov/catalog/PIA16165

[Dysgraphyk]

fresh paper from Mr Lorenz and Neish :
Elevation distribution of Titan’s craters suggests extensive wetlands
C.D. Neish,
R.D. Lorenz
Icarus, Volume 228, 15 January 2014, Pages 27–34


Global study of crater impact show that with the exception of Xanadu (white ellipse on the image), impact craters on Titan occur much more often in highlands (shades of red and orange) than lowlands (shades of blue and green). This new study proposes that craters that formed in wetlands or beneath bodies of liquid were erased almost as soon as they were formed.




comment on science mag news section :

The relatively smooth face of Titan is nothing like the pockmarked surface of our moon. The scars of impact craters are noticeably absent from Titan’s polar regions, for example. And the craters that are present on Titan appear to be much shallower than expected, based on their diameter. Titan has a thick atmosphere, which protects the orb against the impacts of small objects (they’re pulverized as they blaze through the atmosphere) and supports weather and erosion that can help hide or erase craters that do form. As of mid-2001, researchers had tallied 61 definite or potential craters on the entire surface of Titan, most of them 20 kilometers across or wider, says Catherine Neish, a planetary scientist at Florida Institute of Technology in Melbourne. Of that number, 11 have been dubbed “certain” craters, and the remainder are considered either “near certain” or “probable.”

To explain the clear patches, previous studies have suggested various crater-erasing scenarios. For instance, some scientists have proposed that large amounts of sediment carried by streams of liquid methane and ethane from highland areas could have masked lowland craters. But that scenario doesn’t explain the presence of several craters in Xanadu, a broad area near Titan’s equator that is far from any hills.

Similarly, some researchers have proposed that windblown sand may have smothered craters. But that explanation doesn’t wash, Neish says, because most of Titan’s sand dunes are found in highland areas, and there’s no evidence of sand in the crater-free polar regions. Widespread cryovolcanism—the eruption of water, liquid methane, or other volatile substances rather than molten rock—doesn’t explain why craters appear in some lowland areas but not others. Neither does the languid rain of hydrocarbon particles produced by photochemical reactions in Titan’s hazy skies. Those particles pile up at an estimated rate of 6 meters every 1 billion years, not nearly fast enough to obscure a 1-kilometer-or-more-deep crater in the 4.56 billion years since our solar system formed.

But previous studies haven’t considered a scenario in which objects slamming into Titan land in a surface layer of liquid, such as a shallow sea, or in porous, soggy sediments—such as those in the region where the Huygens probe landed in 2005. In such areas, layers of mushy material could be hundreds of meters thick or more, Neish says. Both shallow seas and soggy wetlands—areas where flowing fluids would naturally collect—would be found more often in lowland areas, she notes. Impacts in an ocean, as on Earth, wouldn’t leave a noticeable scar. And an impact that occurred in a wetland would quickly be erased. Almost immediately, the soggy material around the crater walls would slump in to fill the hole. Impacts at wet or soggy sites also typically don’t create a crater with rim that stands high above the surrounding terrain—another reason the cosmic pockmark could be more quickly erased.

Titan’s topographical data bolster this notion, Neish and her colleague Ralph Lorenz of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, contend in the 15 January 2014 issue of Icarus. On average, Titan’s craters are located at higher-than-average elevations. Specifically, half of Titan’s craters lie on terrain 100 meters or more higher than Titan’s average elevation.

The presence of lowland craters in Titan’s Xanadu lowlands—some of the oldest terrain on the satellite—can likely be explained by the age of the impacts, Neish and Lorenz contend. If the craters were blasted before Titan’s atmosphere formed, they appeared when the surface was dry and craters would have remained relatively intact. The weather and other processes that tend to erase large craters wouldn’t have had enough time to hide these pockmarks.

particulary interessting is figure 3 :
showing the trend of distribution of crater shifted to high level terrains.

[titanicrivers]

fresh paper from Mr Lorenz and Neish :
Elevation distribution of Titan’s craters suggests extensive wetlands
C.D. Neish,
R.D. Lorenz
Icarus, Volume 228, 15 January 2014, Pages 27–34

A paste from the above posted quote ... "As of mid-2001, researchers had tallied 61 definite or potential craters on the entire surface of Titan"
I would think that should read "mid-2011" don't you think ??? We were a long way from identifying crater characteristics on Titan in 2001 !

[Dysgraphyk]

A paste from the above posted quote ... "As of mid-2001, researchers had tallied 61 definite or potential craters on the entire surface of Titan"
I would think that should read "mid-2011" don't you think ??? We were a long way from identifying crater characteristics on Titan in 2001 !

For sure, you're right 2011 is probably the right date
Science magazine journalists can make mistake too...


The complete comment in Science is here :
http://news.sciencemag.org/space/2013/11/s...ooth-complexion

[brellis]

Could the age of a crater on Titan be estimated?

[ngunn]

It's a simple and a very fair question so I'll attempt a simple answer. We could get there by either one of two routes. If we knew the rate of impacts of various sizes through time we could date the surface even if only a minority of craters survive. If we knew the timescale of erosion and deposition on Titan (probably different in different areas) we could date the suface and the surviving craters. We know neither. So no.