Interesting Titan stuff at the upcoming DPS meeting Options

[ugordan]

This writeup by Bruce Moomaw was shamelessly copied from the Cassini-Huygens Yahoo group. I hope noone objects (John Sheff ?) posting it here as well because it contains some very interesting new bits of info.

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In addition to the really fascinating- looking new information that will be
released at the upcoming DPS meeting ( http://adams.dm.unipi.it/~dps06/ )
on Titan surface composition data from Cassini's VIMS, there are several
interesting- looking abstracts on its radar data:

(1) Karl Mitchell and Charles Wood have two talks at the "Titan Surface 2"
session on Thursday on the north polar lakes found on the T16 flyby,
suggesting that many (though not all) of them are inside cryovolcanic
calderas. "The concentration of dozens of possible caldera volcanoes in
this northern region of Titan suggests the existence of an extensive hot
spot region of heat loss. This differs from the other 8% of Titan so far
imaged by radar, where volcanic features are infrequent and relatively
isolated." And: "If volcanic and lacustrine environments are concurrent,
then geothermal systems rich in organic materials may provide suitable
conditions for the emergence of life."

(2) In the same session, Randoph Kirk reviews the T13 radar mapping of
Xanadu: "Morphologically, Xanadu is populated with ubiquitous, closely
spaced hills ~5 km across, which locally form chains and appear to be
dissected by numerous channels and low areas filled by radar-dark sediments.
Radarclinometry indicates typical hills are at least 500 m high, but the
results are asymmetric, strongly suggesting that the foreshortened bright
slopes are unresolved. If so, the hills are ~1000 m high with 30 degree
slopes. In either case Xanadu contrasts strongly with the rest of Titan,
where topographic features are rare and mostly <300 m high... We therefore
hypothesize that Xanadu was formed by an initial period of compressive
tectonism and cryovolcanism that triggered the erosion that sculpted the
rugged surface." Sounds less like Mars' Tharsis bulge than I previously
thought, and more like Venus' Ishtar Terra -- commonly thought to be a patch
of surface crust shoved together by a local convergence of underlying mantle
convection currents (like scum wrinkling up together above the drain on an
emptying bathtub. But that would still mean that it's higher-altitude now
than the rest of Titan's surface.

(3) According to Essam Marouf (in Wednesday's "Titan Atmosphere 4"
session), Cassini's radio occultations during its T14 flyby last May showed
clear specular radio reflections off its surface: "The echo appears
consistent with reflection from localized hydrocarbon liquid regions
embedded in mostly nonspecularly reflecting terrain." No description from
the abstract, though, of just what parts of Titan's surface were covered by
this study.

(4) Back at the "Titan Surface 2" sesssion, Jani Radebaugh summarizes the
conventional conclusions regarding Titan's huge networks of longitudinal
dunes, including the idea that they have heights of about 100 meters. But
in a "Titan Surface 3" poster the same day, Flora Paganelli presents an
alternative appraisal of Cassini's dune observations which is a real
eyebrow-raiser.

To wit: Before the T16 flyby, all of Cassini's dune-detecting radar flybys
had involved the craft flying over Titan's surface roughly parallel to the
dunes' long axes -- that is, with its SAR radar beam (which slants off to
one side of the craft) perpendicular to the dunes' long axes, so that it was
assumed that the "light" parallel streaks in the images were from that side
of each dune that tilted toward Cassini and thus reflected back a brighter
radar echo, while the "dark streaks" were the opposite sides of the dunes
that tilted away from Cassini and its radar beam. But during the T16 flyby,
for the first time it flew roughly perpendicular to the dunes' long axes --
and damned if the light and dark streaks didn't show up on the radar with
just as much clarity as during the previous dune observations. This raises
the serious possibility that the "dunes" aren't really dunes at all, with
surface slopes -- but instead "might be superposed streaks with none or
minimal topography, and that they are visible because of differential
erosion between the radar-bright rougher substrate and the radar dark of
fine-particle smooth surface deposits." In short, Titan still retains its
ability to keep totally surprising us.

(5) No less than three entirely new, and very promising, new techniques
have been developed to utilize Cassini's radar for Titan surface mapping in
ways it wasn't originally designed for -- all of them described in "Titan
Surface 3" posters. First, Richard West and Ralph Lorenz discuss the new
"High-SAR" technique in which the radar's scatterometer data is acquired and
processed in new ways to generate genuine and very useful SAR images at far
greater distances from Titan than in its standard SAR mode (albeit, of
course, at lower resolution). So far it's been used at distances ranging
from 11,000 to fully 37,000 km from Titan, with resulting resolutions
varying from 1.5 to 5 km. (The closest of these observations was a second
SAR inspection of Huygens' landing site.)

Second, Lauren Wye describes another way to utilize the radar's
scatterometer data for imaging at 15-km resolution over far bigger areas
than the High-SAR mode (and even obtaining some data on surface
characteristics that neither regular nor High SAR can achieve). Finally,
Bryan Stiles describes how very precise monitoring of Cassini's position and
attitude allow the center of its SAR swath to be used for radar altimetry,
albeit at lower resolution (50 km horizontal and 200 meters vertical) than
the nadir-pointing altimetry for which the system was originally designed.
Sine the latter type of altimetry can't be done at the same time that a
region is SAR-mapped, and since it's become crystal clear that altitude maps
of surface features are absolutely crucial to make any sense out of Titan,
this is very important indeed. But then, given the extraordinary complexity
and continuing mystery of the place, this is true of any new Titan study
technique at all.