[X] My Assistant

[volcanopele]

Titan's Enigmatic Infrared-Bright Spot Is Surface Make-Up
By Lori Stiles
October 06, 2005

http://uanews.org/cgi-bin/WebObjects/UANew...ArticleID=11813

A 300-mile-wide patch that outshines everything else on Titan at long infrared wavelengths appears not to be a mountain, a cloud or a geologically active hot spot, University of Arizona scientists and Cassini team members say.

"We must be looking at a difference in surface composition," said Jason W. Barnes, a postdoctoral researcher at UA's Lunar and Planetary Lab. "That's exciting because this is the first evidence that says not all of the bright areas on Titan are the same. Now we have to figure out what those differences are, what might have caused them."

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The paper, "A 5-Micron-Bright Spot on Titan: Evidence for Surface Diversity" is now published in Science:

http://www.sciencemag.org/cgi/content/abstract/310/5745/92

This article is about Hotei Arcus, an arc-shaped feature in southeastern Xanadu. This feature appears brighter than its surroundings in almost all wavelengths that see the surface, including ISS' 938-nm, but the feature appears exceptionally bright at 5-microns. Another feature with similar characteristics is Tui Regio. I've attached a few views from VIMS from Ta. A close-up of Tui Regio from ISS can be found here

[volcanopele]

Here is the attachment I promised. This graphic uses v1477475933 from the latest PDS release. This is a VIMS cube centered on Tui Regio in Southwestern Xanadu (no PDS release yet for Hotei Arcus). The first 7 images are slices of VIMS cubes are the labeled wavelength, from 0.933 microns out to 4.989 microns. Each of these is of course in a methane window. The next 5 are color composites with various wavelength combinations. Like Hotei, Tui is brighter than its surroundings at all wavelengths, but this albedo contrast is really significant at longer wavelengths as the rest of the surface darkens.

One thing I've noted looking at this cube is the various dark markings in the mid-latitudes of Titan and toward the south near the cloud field. However, the biggest surprise came with Kalseru Virga. This ~N-S stripe of bright material southwest of Tui Regio can be seen in ISS images, as well as in this VIMS cube, but it can only be seen at shorter wavelengths. At wavelengths longwards of 1.590 microns, this feature is not evident, however three dark markings, one near the northern part of Kalseru and two bounding the southern end, become more prominent. Very interesting!

Attached thumbnail(s)

 

[tfisher]

Also interesting is Eir Macula. It looks a different color than anything else around -- for instance in the 2.8/2.03/1.3 color composite, it is sort of a purple color, unlike anything else. This is because it is dark at 2.03 microns but bright at 2.8.

(Do I have it right, that Eir is the one that is bright at 2.8, not the patch slightly to its west that is still dark at 2.8 microns?)

Anyway, very cool stuff. I'm attaching a clip from the USGS feature name chart for reference. (I hope this works...)

[volcanopele]

Good catch! I didn't see that. Yeah, it does look like Eir Macula has strange spectral properties, dark at 2.03 microns and shorter and brighter at 2.8 microns and longer. Interesting. Can't wait to see the VIMS team come out with a paper about this

[Olvegg]

And what could be these white dots at 4.989 microns? Are they real or just artifacts? It seems like one of them appears at wavelength 2.799 (upper right), but not exactly in the same place.

[Guest_Richard Trigaux_*]

Eir Macula could be a lake, at least a dried up lake bed. Eventually it may drain some dissolved minerals from the surrounding "mountains" (I put quotes as these mountains could be only one hundred metres high) After these minerals are deposed on the bottom of the lake, where they even cover the usual dark matter in the hollows. Such local evaporites deposits are very common in Earth deserts, where we can often see white salt in the bottoms.

Eventually it may be the only actual lake found to date, and from there its unique colour without the usual dark matter.

[volcanopele]

And what could be these white dots at 4.989 microns? Are they real or just artifacts? It seems like one of them appears at wavelength 2.799 (upper right), but not exactly in the same place.

Those are just noise hits. The signal/noise ratio at 5 microns is pretty low, so bright pixels like those are not uncommon.