[X] My Assistant

[Guest_AlexBlackwell_*]

Although the mission description document for the upcoming (February 27, 2006) T11 flyby hasn't been released to the public yet, here are the science highlights:

Imaging Science Subsystem (ISS) – will perform a global-scale mosaic of the sub-Saturnian hemisphere: covering the equatorial region from Fensal/Quivira/Aztlan to Aaru, and Tsegihi in the south. ISS also has a mosaic that ranges from the regional scale to high resolution and includes the southern part of Aztlan, the eastern part of Shiwanni Virgae, and Elba Facula. The closer mosaic will have pixel scales ~600-350 m.

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 airmass 1.5-2.0. POINTING: -y to Titan, x away from sun.

Ultraviolet Imaging Spectrometer (UVIS) – will perform a global spectral map to study aerosol scattering and hydrocarbon absorption and distribution. This will also be UVIS’ first solar occultation. With the solar occultation UVIS can observe the extreme ultraviolet (EUV) spectrum below 110 nm and can sample opacity from nitrogen and methane and possibly some other hydrocarbons.

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 take advantage of this encounter being upstream of the Titan/magnetospheric interaction. The spacecraft will fly through Titan’s middle ionosphere. Together with the T8 and T6 flybys, T11 will allow MAG to reconstruct the upstream equatorial ionospheric pile-up region.

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 study the interaction of the magnetosphere with Titan at intermediate distances for evidence of ion pickup, radio emissions, density profiles, and the general wave environment.

Radio Science (RSS) – will perform two Gravity Science Enhancement (GSE) passes occurring after the flyby in order to answer the question of whether Titan possesses an internal ocean. The GSE passes are crucial to de-correlate Titan's GM from the distance at closest approach.

[David]

Here's a hopelessly obvious question, but one I've not seen the answer to. Most of the "dark stuff" (whatever it is) on Titan is concentrated in a connected, not-too-wide band that goes almost all the way around the equator. and some tens of degrees north and south of it; there are some blotches further south, and of course we can't see all of the northern hemisphere, but there's nothing in the part we can see north of the band.

Have there been suggestions for this peculiar distribution? Or isn't it worth commenting on?

[JRehling]

Here's a hopelessly obvious question, but one I've not seen the answer to. Most of the "dark stuff" (whatever it is) on Titan is concentrated in a connected, not-too-wide band that goes almost all the way around the equator. and some tens of degrees north and south of it; there are some blotches further south, and of course we can't see all of the northern hemisphere, but there's nothing in the part we can see north of the band.

Have there been suggestions for this peculiar distribution? Or isn't it worth commenting on?

The equatorial "stuff" is bounded by linear borders suggesting a tectonic origin: something like the Valles Marineris on Mars, but going more or less all the way around. Note that VM is pretty much parallel and near the equator of Mars. And Venus also has a roughly equatorial band of tectonic activity. Note that an oblate geoid could focus tectonic activity on the equator, while dissipation of angular momentum can move the axis of rotation so as to put the equator where an existing band of varied mass concentration lay!

So it seems, one way or another, Titan, which probably expanded as it froze, ended up faulting around what was or what became the equator and the decrease in altitude on that band provided a basin into which dark sediment eventually settled.

Since ISS shows Titan in monochrome (and VIMS hasn't shown the high latitudes all that well, and has had other limitations), we can't be sure that the equatorial dark stuff and the southern dark stuff are the *same* dark stuff. I suspect that the southern dark stuff is either seasonal wet areas that is only dark *now* (and might dry up next season) and/or areas that have accumulated sediment from frequent (seasonal?) past or ongoing wet seasons that filled "local" basins with the same kind of stuff that filled the equatorial tectonic basin(s).

This is somewhat speculative, but then we don't have all the data we'd like. Yet.

[The Messenger]

The equatorial "stuff" is bounded by linear borders suggesting a tectonic origin: something like the Valles Marineris on Mars, but going more or less all the way around. Note that VM is pretty much parallel and near the equator of Mars. And Venus also has a roughly equatorial band of tectonic activity. Note that an oblate geoid could focus tectonic activity on the equator, while dissipation of angular momentum can move the axis of rotation so as to put the equator where an existing band of varied mass concentration lay!

So it seems, one way or another, Titan, which probably expanded as it froze, ended up faulting around what was or what became the equator and the decrease in altitude on that band provided a basin into which dark sediment eventually settled.

This is somewhat speculative, but then we don't have all the data we'd like. Yet.

Fascinating. The most obvious question is: Why isn't the Earth tectonically belly-banded?