Saturday, April 09, 2005

LPSC Notes Part 4

Even more...
  • Channels and Fan-like features Conclusions
    • SAR-bright channels, associated fan-like features, and flows suggest the presence of transported material w/ different radar properties than the surrounding materials
    • while surface roughness drives much of the reflected signal from terrestrial surfaces, Titan's observed volume backscattering implies that near-surface structure or compositional change could, to some extent, define surface features
    • Two possible explainations based on SAR and Radiometry data at these features
      • SAR-bright return is associated w/ a high component of volume backscattering possibly due to presence of low absorbing porous material (a mixture of low and high dielectic constant)
      • SAR-bright return results from a high component of volume backscattering derived from fluvially-transported and deposited hetereogenous materials (ice-rocks) of a size greater than the operational radar wavelength of 2.17 cm; here the SAR-bright linear features might be associated w/ fluvial (most likely hydrocarbon) channels and the fan-like features then be alluvial in nature
  • Impact craters from RADAR
    • crater identification hampered by volume scattering and other round features like calderas
    • 80-km wide crater in T3 swath
      • impact crater?
      • dark ejecta blanket - 150 km - impact melt?
      • parabolic bright deposit 260 km+
      • sharp rim crest
      • gullies on wall
      • flat floor, no central peak
      • two tone floor - aeolian?
      • strongly modified crater interior, but...
      • small scale features preserved outside crater in ejecta blanket - relatively young
      • relation to dark linear features in dark terrain?
      • nearby round features - old craters?
    • 440-km multi-ring basin
      • moat - crater lake?
      • wind streaks or wavecrests near south east rim
      • downslope fluvial features along eastern and south eastern rim
      • gullies in rim
      • hummocky central region

I guess that's it for these. I might post more next week. For now, I think that's enough ;)

LPSC Notes Part 3

I guess I wrote down more than I thought, so here is more:
  • RADAR Lakes/Dark Spot - Lorenz
    • sharp boundaries
    • typically 10-15 km across
    • cardoid or crescent shaped
    • emission is a bit stronger
    • crater lake at circus maximus?
    • Seasonal effects on distribution - more "lakes" in far north
  • VIMS topography
    • ridges found through shape-from-shading, a few hundred km - 10 km between ridges
    • possible H2O and NH3 features in bright regions
    • perhaps the bright regions are the theorized ammonia-water cryovolcanic eruptive material
  • Photometric studies with VIMS - Nelson
    • I/F values - bright 0.168, bright intermediate 0.138, low 0.07
    • tau may increase values by 20% or more
    • no evidence for large accumulation of flat lying liquids
    • older surface, slow erosion
  • VIMS Observations of Titan's surface - Rodriguez
    • Ta hires - 1.8 km/pixel - snail
    • 30 km diameter bright feature w/ two elongated wings extending west
    • 1 pixel much darker than surroundings at center of feature
    • cryovolcanism with caldera at center
    • E-W darker linear feature
    • Tectonic features or flow lines
    • similar to Ganymede's grooved terrain?
    • not pure water ice
      • 2.67 microns/2.75 microns > 1
      • other constituent absorbs at 2.67 microns
  • RADAR Mapping - E. Stofan
    • wavelength = 2.17 cm
      spatial resolution 400m-1km
    • swaths 120-450 km
    • incidence angles - Ta=<10-30 deg; T3=15-45 deg
    • volume scattering may be important due to ice, hydrocarbons, ammonia-ice mixtures, tholins
    • units
      • 8 basic units (2-3% of planet)
      • distinctions - radar brightness, planform shape, slope
      • boundaries on T3 obscured by apparent surficial deposits
      • sinuous features
      • Impact craters
        • 2 craters in T3
        • none w/ confidence in Ta
      • Homogenous Unit
        • dominant in Ta (50-60%)
        • less common, brighter in T3 (20%)
      • mottled unit - boundary gradational
      • bright mottled unit (T3) - Xanadu
      • Bright lobate unit
        • cryovolcanic flows
        • lobate
        • sheet-like and digitate
      • Bright lineated unit
        • fan shaped deposits
        • grooved
      • dark mottled unit - smooth, mobilized unit
      • hummocky unit - small, isolated hills, center of circus maximus, end of Ta
  • Cryovolcanism as seen by RADAR - Lopez
    • Ganesa Macula
      • channels 91 km in length
      • 23 km depression in middle
      • flow south and east from central pit that runs over edge
    • Large flow
      • 49N, 43W
      • 23,700 km2
      • 100-200 km in length
    • western caldera - 18 km across
    • eastern caldera
      • ~13 km
      • area 1235 km2
      • flow thickness - 200-300 m
    • ammonia-water flow viscocities similar to silicates - consistant with flow thickness
  • Channels and Fan-like features
    • between Ganesa and giant flow, resolution jumped from 500-1000 m/pixel
    • channels 1000 meters across
      • drainage not fully developed
      • low order, short lasting drainage present
      • depositional surface ha the same SAR bright return as the channels
      • channels could represent erosional surfaces leading to triangular fan deposits
    • Channels near Circus Maximus
      • rim 430 meters high
      • channels 500m-1km across extend for 100-180 km on a ENE sloping surface
      • fan features
      • accumulation surface
      • lineations/flow lines/cracks?
      • dendritic drainage at crater rim
      • presence of transported materials w/ different radar properties than surrounding surface

LPSC Notes Part Two

After some delay, here is the second half of my notes from LPSC:
  • Cassini RADAR
    • Radiometry
      • not an iceball
      • dielectric constant ~ 2.1
      • a lot going on
      • N-S gradient, 2.1 in north, 1.6 in south
      • organic material ~ 2-3
    • Scatterometry Ta inbound
      • multiple populations of terrain types
      • coorelate w/ optical albedo
      • optically dark -> radar dark -> warmer
      • optically bright -> radar bright -> cooler
    • High resolution radiometry
      • bland dark - higher brightness temperature
      • argues for importance of volume scattering role of organic contaminents
      • Xanadu - mottled
    • RADAR dark features in plains - smooth, localized
      • kitty head - 56W, 50N
      • west ponds in Ta - 124W, 37N
    • Ganesa Macula
      • cryovolcanic dome akin to pancake domes on Venus
      • degraded topography along margins
      • deltas connected to bright lines
      • rough center - pit
    • Cryovolcanic features - 43W, 49N, 40 km caldera
  • VIMS - Bob Brown
    • Phoebe
      • compositionally diverse
      • water everywhere (bound or free)
      • ferrous iron
      • 2.2 micron absorption - cyanides
      • 3.3 micron absorption - C-H organics
      • CO2 - complex inclusion in minerals - found in dark materials
      • a bit more ice at the poles
    • Titan
      • emission at 1500 km - atmosphere more extended than once thought
      • snail - geology from VIMS possible
  • CIRS
    • Detected species - CO, N2, CH4, C3H4, H2, C4H2, CO2, C2H2, C2H6, C2H4, CH3D
    • Stratosphere - 310 km - max temp
    • upwelling at southern latitudes w/ adiabatic cooling
    • circumpolar vortex in north - high winds in north
    • wind jets change with seasons
    • zonal variations in temperature weak
    • HCN seen at high northern latitudes
    • CO2 disappears as you move north
    • CO2 increases with depth
    • winter polar atmosphere isolated - akin to terrestrial ozone hole
    • strongest winds 160 m/s at 20-40N
    • summer pole 5K colder than equator in the stratosphere
    • CO stratospheric mole fraction 4.5 +/- 1.5 x 10-5
    • CH4 mole fraction in statosphere 1.6 +/- 0.5 x 10-2
  • UVIS
    • Instruments
        FarUV (110-190 nm)
      • EUV (55-110 nm, solar occultations as well
      • High speed photometer
      • HDAP (D/H ratio)
    • Tb Stellar Occultations
      • Lambda Sco + Spica
      • vertical profile of constituents
      • Lambda Sco - 36 South Latitude
      • CH4, N2, C2H2, C2H4, C2H6, HCN, C4H2
    • Tmin - 114 K near 615 km
    • Phoebe
      • H2O, CO2, frosts contribute to Phoebe' FUV spectrum
      • latitudinal variations
      • no emissions (not Chiron)
      • very dark <>
    • ion composition
      • No N+ near Titan
      • maybe it comes from icy satellites
      • O2 atmosphere over rings
      • H2/O2 loss rate ~10
  • Magnetometer
    • magnetospheric interaction with Enceladus similar to Io and Jupiter
    • Saturn's magnetic field is being bent around moon
    • either very dense atmosphere or higher production of ions
    • wave activity H2O+ - Alfven wing
    • 2 Re extent
    • no firm density number
  • Aerosol and Cloud Properties from DISR
    • 8 particles/cm3 rather uniform assumes 256 monomers/particle and 0.05 micron monomer size
    • HRI images with lamp on - backscatter off haze
    • optical depth @ 830 nm @ surface 1.5
    • optical depth @ 531 nm @ surface - 6
    • aerosols larger than thought
    • aerosols extend to the ground

Friday, April 08, 2005

New Titan Image: Titan Mosaic - East of Xanadu

CICLOPS has released this beautiful mosaic of the H region on Titan. In fact, this may be the best mosaic ever created from spacecraft images...okay, maybe I shouldn't go that far ;) Seriously, this is a mosaic of 18 narrow-angle footprints, each with resolutions between 1 and 2 km/pixel. Behind these frames are three larger scale images, one a full-disk wide-angle image taken at the same time as these images, and the other two from the distant encounter in early July 2004.

Lots of great features can be seen in this mosaic. Above center, a dark NE-trending diffuse dark streak can be seen. This feature appears to have some eolian control, and maybe strictly an eolian feature, however, my feeling is that we have something more going on. One possibility is that this is a crater penumbra, a dust streak derived from cratering material (or from material from a "failed" meteorite, a la Tunguska). Another possibility which I favor is that this is from a geyser. We know that methane outgasses from the interior based on the lack of surface liquid and the lack of Argon-36 combined with the presence of Argon-40. This maybe an outgassing site where the dark diffuse deposit is derived from material that was carried aloft by the methane. The orientation maybe an indication of altitude (i.e. below the boundary layer at 5 km).

Other interesting features include a series of fractures south of the H, the RADAR 80-km crater with its partially dark floor in near-IR, the VIMS "palimpset", and a jumbled terrain region south east of the crater. In addition, there appear to be "tendrils" leading to the southeast from the big island in the middle. These features have led to the suggestion that surface winds in this region may not be west-east everywhere, but maybe Northwest-southeast in this region.

New Titan Movie: Titan's Shifting Hazes

CICLOPS has released a movie of violet filter frames of Titan's north polar hazes. These hazes have been observed before but not at the temporal resolution to create a movie like this. Not sure what these motions tell us, I'm not an atmospheres person. But it is very cool nevertheless.

New Titan Image: Saturn through the Haze

This is very neat image showing Saturn over Titan's north polar hazes shortly after closest approach. This is also useful since we can examine the light gets diffused through the hazes by looking how Saturn's reflected light changes.

New Titan Image: Titan's High Hazes

This image from T4 show structure in Titan's stratospheric hazes. Structure is ususally most pronounced in the north polar regions. Cassini scientists continue to work on why this is the case and to understand the specific structures seen here.

Updated Saturn System Maps

Steve Albers has some great maps of the Saturn system satellites on his website that include images taken by Cassini over the last few months. Personally, I use my own Titan map, but his maps of Tethys, Enceladus, Rhea, and Iapetus are about as good as I've been able to find them. The Enceladus, Rhea, and Titan maps have been updated in the last week or so to include data from the last month of Cassini images. In addition to Saturnian system maps, his Io and Europa maps are very well done. So if you are looking for maps, that would be a good site to check out.

Thanks to alan over at the Unmanned Spaceflight forum for the heads up on the update.

Cassini Significant Events for 03/31/05 - 04/06/05

The Significant Events report for this week is out, though it doesn't seem to have shown up on the JPL website yet but it has gone out to certain mailing lists. The big event over the last week has been T4. This was the first encounter of Titan in which we were just on reaction wheels rather than thrusters (which require precious hydrazine) to control stability and pointing. Thrusters are usually needed when the spacecraft dips below 1100 km altitude (give or take 100 km) from Titan because of torques applied to the spacecraft by Titan's, which, while thin at that altitude, is still dynamically significant. Anyways, based on the telemetry acquired after the encounter, the reaction wheels appeared to work nominally and were sufficient for controlling the spacecraft with a flyby at 2400 km (I would hope so!!). Interesting that ISS was not mentioned in this part but other instruments were...

This release also confirms that the Tethys tweak, calling for a new targeted flyby of Tethys, has been officially approved. I guess it was only provisionally approved, or approved by a smaller working group last week. The Tethys tweak came out of a requirement to avoid the E-ring crossing on Rev15. A 1500-km Tethys targeted encounter shook out of this required change. IOW, the trajectory needed to be tweaked to avoid this crossing, and it only required a little extra delta V to produce this targeted flyby and a closer flyby of Hyperion a few days later (1000 to 500 km). Apparently, nearly a dozen science objectives from the Cassini AO will be accomplished by this tweak (not bad!).

DISR Update

There has been an update on the DISR website. Looks like they are holding their products for the Nature publication coming in the next month or so. This explains the lack of mosaics in the last couple of month. Not completely surprising, ISS did the same thing with their map, withholding it till their paper publication. But you can stop loading their page everyday, like me :D

New Hyperion Image: Hyperion's Face

CICLOPS has released this magnified view of Hyperion, taken in February. Hyperion is still only seen at low resolution though that will change on June 9 and September 25 as Cassini flys by this strange, tumbling moon. The June 9th encounter will be more distant but will provide better images than those taken by Voyager. The September 25th encounter will be the closest encounter Cassini will make of this small satellite, skirting it by 500 km (down from the original 1000 km close approach in the original tour plan, before the "Tethys Tweak" to avoid a dangerous E-ring crossing).

Thursday, April 07, 2005

Plethora of Raw images

Looks like there has been a data dump of raw images from the last week on the JPL Raw images page:

Wednesday, April 06, 2005

Press Release: Cassini Mission Status Report

JPL has put out a press release announcing the successful Titan flyby of last week. They report some recent issues have been occuring on the Composite Infrared Spectrometer (CIRS) related to jitter on one of the mirrors as well as issues with motors on MIMI and RPWS. However, overall JPL is reporting that excellent data was returned on this flyby.

New Titan Image: Titan's Mask

CICLOPS has released this contrast enhanced view of Titan taken last month showing the H region that has become a focus of investigation on this most recent flyby. This view was taken in the clear filter, so photons are reaching the detector from all wavelengths it is sensitive to, from UV to near-IR. Surface photons only make up a small contribution but it one of the three primary sources of brightness variation across the disk in this range, in addition to the hemispheric asymmetry in the haze brightness and the haze layering visible near the north pole.

Tuesday, April 05, 2005

New Titan Image: New Titan Territory

CICLOPS has released sharpened view (shock a sharpened view of Titan I didn't make) from last Thursday's flyby. This view shows the H-region on Titan, a feature first discovered by ground-based observers a few years before Cassini's arrival. Cassini, prior to this encounter, had observed the southern portion of this mosaic at moderate resolutions, but the H itself has not been viewed at higher resolutions that 60 km/pixel. This image, at 7 km/pixel, is but a taste of what's to come as this is one of the Wide-angle images taken during a medium resolution mapping that show these same features at even higher resolution (5x higher than this image). However, Cassini RADAR has SAR swaths that do cover this area. The Ta SAR swath covers the very northern portions of this image and while the T3 swath covered low to mid northern latitudes.

Some features in common can be seen in this image and in the T3 SAR swath. The dark spot with a patch of bright terrain just right of center is the 80-km wide crater seen by RADAR. though it appears that some of the details on the shape of the "ejecta blanket" may differ between the two instruments.

So I'll open this image up for discussion, though you may want to wait a day or two...

New Cassini Image: Rhea and Enceladus

CICLOPS has released this view of Rhea and Enceladus as they were seen in the same Narrow angle camera field of view on February 21, 2005. Rhea is in the background but because it is so much larger than Enceladus, it still appears bigger than Enceladus in this view.

Monday, April 04, 2005

LPSC Notes coming soon

I know I keep putting off posting the rest of my LPSC notes but to be honest, there isn't a whole lot to talk about that isn't already in the public domain, especially after the two excellent Planetary Society articles. I will try to post them tomorrow but I may get so busy that I won't have a chance.

More Titan Raw images

CICLOPS has released a number of raw images of their own, so you download these images without the "evil" of JPG image compression if you so choose.
Also dilo over at the Unmanned website has produced a mosaic of the raw images of the surface.