[X] My Assistant

[Guest_AlexBlackwell_*]

Since Emily posted in her LPSC notes:

"So, so much for Titan. All in all, there wasn't a lot that was new, either new data or new insight. I wish now that I'd skipped the latter part of the Titan session and gone to the rovers, but it was too late for that. The radar story will get more interesting, because after a long hiatus in the acquisition of radar data they are going to be getting a lot more radar passes beginning with the T13 flyby on April 30, so there is much to look forward to there."

I guess I'll go ahead and post the science highlights for the T13 flyby:

T13 - Science Highlights

Imaging Science Subsystem (ISS) – will observe particle properties, vertical distributions (~6 km/px. 0.6 Mbit/frame with 2x2 summing). ISS will also examine wind/cloud motions; (3-12 km/px, 3 images/timestep in CB1 filter to increase SNR), and search for and monitor lightning/aurora. (high-resolution imaging, 50-200 m/px, special targets, emission angles < 45 prefer IR-polarizer (phase 45-110)).

Cassini Plasma Spectrometer (CAPS) – will investigate large-scale and distant aspects of the Titan interaction by observing during entire period around an encounter from 10 to 25 RS.

Composite Infrared Spectrometer (CIRS) –will obtain information on trace constituents in Titan's stratosphere. Integrate on limb at two positions POINTING: Obtain information on CO, HCN, CH4. Integrate on disk at air mass 1.5-2.0. POINTING: -y to Titan, x away from sun.

Ultraviolet Imaging Spectrometer (UVIS) – will observe star Beta Ori as it becomes occulted by Titan’s atmosphere.

Visible and Infrared Mapping Spectrometer (VIMS) – will obtain new high resolution images that will help understand Titan's geology and the fate of CH4.

Magnetometer (MAG) – will investigate large-scale and distant aspects of the Titan interaction by observing during entire period around an encounter from 10 to 25 RS. (23TI (T13)) T13 is an equatorial wake flyby under plasma conditions near Saturnian local midnight with 1852 km altitude at CA. Thus it is very similar to T11 even according to local time.

Magnetospheric Imaging Instrument (MIMI) – will investigate micro-scale and near aspects of the Titan interaction by observing during about one hour period around an encounter. With -Y pointed toward Titan, when within 30 minutes of the targeted flyby, optimize secondary axis for co-rotation flow as close to the S/C -X, +/- Z plane as works with the other constraints on pointing. Also, measure Titan exosphere/magnetosphere interaction by imaging in ENA with INCA (when sun is not in INCA FOV).

Ion and Neutral Mass Spectrometer (INMS) – will obtain data regarding Titan’s atmospheric and ionospheric composition and thermal structure. INMS will also observe the magnetospheric/ionospheric interaction.

Radio and Plasma Wave Spectrometer (RPWS) – will perform observations in the immediate vicinity of Titan, including thermal plasma density and temperature measurements with the Langmuir probe, search for lightning and other radio emissions, characterization of plasma wave spectrum, search for evidence of pickup ions. Langmuir probe within 90 degrees of spacecraft ram at closest approach, co-rotational ram outside of +/- 15 minutes.

RADAR – will perform low and high resolution SAR (Synthetic Aperture RADAR) imagine of Titan’s surface. Additionally, RADAR will collect Altimetry, Radiometry, and Scatterometry Data.

[Guest_BruceMoomaw_*]

Marvelous new SAR images. Regarding the ambiguity as to whether the circular features we're seeing are craters or calderas, there was yet another LPSC abstract at http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1659.pdf . It's beginning, however, to look more and more ominously possible that Cassini's coverage of more and more of Titan's surface area may not enable us to understand much more about just what it is we're actually looking at -- for that we'll need higher resolution, which Cassini cannot provide.

(A pity that features on Titan aren't named after famous monsters of myth. In that case we could have "Dracula Facula".)

[ngunn]

Regarding the ambiguity as to whether the circular features we're seeing are craters or calderas, there was yet another LPSC abstract at [url=http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1659.pdf] .

Regarding the circular features: Impact craters and volcanic calderas are mentioned here, but are these the only possibilities? What sort of appearance would we expect from the remains of an ice/clathrate diapir that slowly made it all the way to the surface, rather like a terrestrial salt dome? (A kraken rather than a vampire?)

[volcanopele]

Regarding the circular features: Impact craters and volcanic calderas are mentioned here, but are these the only possibilities? What sort of appearance would we expect from the remains of an ice/clathrate diapir that slowly made it all the way to the surface, rather like a terrestrial salt dome? (A kraken rather than a vampire?)

hmm, kinda like those lenticulae on Europa. Not quite sure how those would look in RADAR.

The problem with identifying impact craters on Titan is that very few are prestine (if you can call Sinlap prestine, assuming that it doesn't have a central peak due to crustal thicknesss at the time of formation). With Venus, identifying craters was easy since nearly all of them were very classic impact craters, with only a few showing modification since their formation. This is part of the evidence that Venus' surface was catastrophically resurfaced, though you can get the same look other ways. On Earth, in SAR data you can identify vaguely crater-like features as craters because you can go to the site and identify rocks and structures that support that conclusion, a luxury we don't have (yet) on Titan. So the lack of prestine craters and ground truth does make it more difficult to firmly conclude whether a feature is a crater or not. This is especially difficult for ISS since we can only see albedo, a dark material doesn't have to fill the entire floor, making a circular dark spot, and as we found out at Shikoku, dark material doesn't need to fill it at all.

Could this abundance of channels be somehow related to the topography of Shikoku – but why should that be so much different from Adiri, which also contains mountain ridges/ hills/ elevated terrain?
Or are the channels derived from underground methane released after the formation of the impact crater in NE Shikoku. However they appear to run parallel to the crater rather than starting from it. Furthermore, they seem to be more branched than the rather primitive looking channel features E of Menvra (in the T3 SAR picture PIA07366 - Huygens Landing Site Similarities). So could they possibly be the result of rainfall? Interesting!

Good point. either there is a difference in climate patterns between this region and Adiri, or these channels are spring-fed, and only small or no springs are found in Adiri. I'll have to take another look at the T8 swath.

However, for people who are fond of channels – like me - I could imagine that the T16 SAR swath at July 22 (which should cover regions close to the – presumably much wetter – north pole) will probably be a dream come true.

Could also be one of our best chances to see a lake in RADAR data, though I would be surprised if some of the very smooth areas in T7, T8, and T13 turn out to be playas.

Oh speaking of which, Emily has posted on her blog a brief description of the Xanadu portion of the T13 swath. The RADAR team presented a giant printout of the swath at the OPAG meeting yesterday, where she got a look at it. She mentions the abundance of mountainous terrain, but without the apparent mountain chains seen in the T8 data. More like the Titan equivalent of the Tibetan plateau (but not THAT high up...). She also mentions an abundance within Xanadu of drainage channels. So I'm sure you'll be happy as a clam tracing out those channels, Thorsten. Hopefully cutouts of parts of the Xanadu portion will be released shortly.

In addition, Emily mentions Dennis Matson's full description of what happened on Monday with the downlink problems. I am just glad that I didn't hear about it until after data did finally start coming down.

[ngunn]

QUOTE(ngunn @ May 5 2006, 04:15 AM)

Regarding the circular features: Impact craters and volcanic calderas are mentioned here, but are these the only possibilities? What sort of appearance would we expect from the remains of an ice/clathrate diapir that slowly made it all the way to the surface, rather like a terrestrial salt dome? (A kraken rather than a vampire?)

hmm, kinda like those lenticulae on Europa. Not quite sure how those would look in RADAR.

A bit of follow-up on the above. I've just read this paper linked by Alex today in 'Venus Express':
http://www.blackwell-synergy.com/doi/abs/1...04.2006.47316.x

The Venus coronae sound like the sort of thing I was trying to suggest as a possibility for Titan. They are very varied but mainly circular-ish with different concentric arrangements of high and low topography. Apparently the rising diapir hypothesis can account for the various forms by varying such parameters as crustal thickness/layering and the stage the process has reached. Richard, you mentioned circular forms on Titan that might be diapirs also. Have you read about the Venusian coronae and do you think there could be a parallel?