Sunday, March 20, 2005

LPSC Initial Notes

I got back from the Lunar and Planetary Sciences Conference in Houston yesterday. I took quite a few notes but it may take a while for the lot of them to be posted here. So expect some notes to be posted each day this week. However, here are a few key highlights I thought I should post now:
  • Both the Magnetometer and MIMI observed an atmosphere at Enceladus, but UVIS did not (another instrument that won't be revealed here just also detected gases in the Enceladus region). MIMI and the Magnetometer detected an interaction between Saturn's magnetosphere and Enceladus consistent with a "dense" atmosphere 2 Enceladean radii in extent. The magnetometer observations might also be consistent with a higher production of ions in Enceladus' environment. UVIS did not detect an atmosphere at Enceladus, putting an upper limit on any atmosphere of 2-3 x 10^8 atom/cm^3 in density. Also, no oxygen emission was seen at Enceladus by UVIS.
  • The CIRS and UVIS presentations on Iapetus suggested another possible formation mechanism for the dark terrain. Rather than dark material being deposited on the surface, the two teams suggested that the lack of water ice could be due to the removal of bright ice material from Cassini Regio, leaving behind the dark, carbonacous, fluffy material. Interestingly, Phoebe, which according to some theories is the source of the Iapetus' dark material, is more similar to Iapetus' bright terrain in composition than the dark terrain. For ISS, the north polar bright terrain was seen to be lower in altitude in MOLA-like DEM maps than the dark terrain though the map still needed the proper tri-axial ellipsoid solution.
  • Peter Lanagan presented a formation model for the cryolava flow seen near the "runway" feature seen in Huygens DISR images.
  • Enceladus' density is the highest of the inner icy satellites, third of the Saturnian satellites with only Titan and Phoebe having greater densities. The density of Enceladus is 1.6 g/cm^3.
  • The near surface winds detected by Huygens were very weak, on the order of 1-2 m/s and in fact, DISR images indicate that Huygens moved roughly eastward until around 3 km altitude when Huygens swung northward and in fact a little westward. Thus, at the lowest scale height, zonal winds are weaker than rotation. Given this information, the poles are warmer during summer in a narrow zone near the surface. This is not surprising given the level of storm activity near the poles during summer.
  • RADAR radiometry detected a gradient in dielectric constant from north (~2.1) to south (~1.6) indicating an increase in organic material from north to south. RADAR scatterometry demonstrated that optically dark (radar dark) materials were warmer than optically bright (radar bright) materials. This pattern breaks down though in the "French Coast" region of Southwest Xanadu, which is optically bright but warmer in radar scatterometry. In RADAR SAR, the team is interpreting the "cat scratches" as longitudinal dunes, long dune forms that are parallel to the prevailing wind direction. These are often seen in the Sahara desert and in the Simpson desert in Australia on Earth. Given their prevalence on dark material, it is quite possible that dark material are not bodies of liquid, but seas of sand. Finally, the RADAR team is interpreting many of the round features seen in Ta as cryovolcanic features such as lava domes or calderas. In RADAR altimetry, much more relief was detected, including a 200 meter drop over 2 km and 400 more meter downward slope over another 300 km.
  • GCMS detected Argon-40, Ethane (C2H6), Ethanedinitrile (C2N2), Acetylene (C2H2), and Carbon Dioxide on Titan's surface.


Anonymous Gsnorgathon said...

Jason - thanks so much for writing all this up! I'm looking forward very much to your later installments.

That bit about Enceladus's density is a bit of a shocker to me. Was this widely expected? Most figures I've seen elsewhere are in the range of 1 - 1.3 g/cm^3.

3/21/2005 04:44:00 PM  
Blogger Jason said...

The higher density at Enceladus is largely a surprise given its apparent high water ice content if you go by the surface spectra alone. Again, this lends credience to the idea that the pure water ice surface is a coating emplaced by geysers, its atmosphere, and/or the E-ring.

3/21/2005 05:06:00 PM  

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