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January 15, 2005

Update on Huygens - Titan - 1/15/05

More science analysis from John Strickland:

The E.S.A. science press conference was held at 5:00 am Eastern Time (1/15/05), and some annoying news was revealed. One of the two main data channels from the Huygens was not received on the Cassini spacecraft. This was caused by a fault in European software commanding the European receiving hardware installed on Cassini. Half of the predicted 700 images were lost, and data from a Doppler experiment that would have helped establish location and wind motion better was lost. A lot of the photos at altitude are redundant, but some of those taken close to the surface are not. After the probe actually hits the surface, images in only 1 direction can be taken, since the probe is no longer spinning. Radio-telescope data may help to locate the probes position to within about 1 km.

The probe came out of the haze layer at about 12-15 miles high, and immediately started to get spectacular images. A temperature profile was produced which clearly shows the troposphere as a distinct temperature layer. Methane abundance rose as the probe neared the surface. Only a few scientific measurements have been released so far. A major revelation seems to be the division of the surface into rough, hard light-colored terrain and smooth, dark-colored terrain. A wind was blowing about 22 miles an hour at altitude, which caused the probe to drift from over the light colored area that was below it when it emerged from the haze deck, and over a dark area further to the east.
The basic question you want to ask when first seeing such an alien terrain is "What are we actually looking at? When the probe was still about 8 miles high, it took a spectacular panorama (made of 10-15 smaller images), looking back (possibly west) at the "coast" or edge of the light colored terrain (covered with the dendritic (stream-like) pattern, and in the other direction, with a vivid series of tapering streamers or bands of white material converging apparently toward the east on top of the dark material. The edge of the light terrain appeared to be higher and rough, with dark shadowed cliffs, (but this may be a visual illusion - we need to wait for confirmation with more images from different altitudes.) It turns out that the second image released yesterday, with the tapering geometric markings, is part of that white on dark area with converging streamers. The dark area in the first image is apparently south of the dark area covered with the light bands.

The fact that the probe landed on very flat terrain with rocks that are whiter than the surface they rest on could indicate that the rocks are made of the same material as the light-colored terrain. If the rocks are water ice, the light colored terrain may also be water ice. Therefor, the tapering light-colored areas on the dark areas may be bands of the same rocks seen by the surface image. This means they are too heavy to be moved by the wind into the streamer-like patterns. Dr. Ingersoll (Principal Investigator for the Descent Imager - Spectro-radiometer) suggested that the dark area may be a wide flood channel and the rock bands may be gravel banks left behind by a ancient flood.

We can also possibly regard the light terrain as "bedrock" (made of ice?) and the dark terrain as a wide channel filled with alluvial material. (Last year they thought that the light areas were organic and the dark areas were ice. This is now thought to be wrong.) The probe showed that it landed on a surface with the consistency of mud or clay. Could the alluvial deposit be made of "sand" grains of ice mixed with the organic goop? The narrow dendritic channels on the light colored terrain may also be draining the organic goop, along with pieces of the "bedrock", but to where?. One problem with this argument is that none of those channels seemed to be draining towards the dark, flat, and presumably lower terrain.

The wide panorama was obviously taken at a much lower altitude than the earlier images, since the features on the light, rough terrain are very strongly foreshortened. However, in the panorama, a white band (of possible ethane fog droplets) can be seen right along the now distant edge of the light terrain. This does not show up in the higher image shown yesterday, and is presumably visible due to the low angle of sight along the distant surface. The panorama image also shows both terrain types as being more similar in brightness, indicating that most of the dark area may be covered with a very thin layer of the same fog.

We will have to wait for more of the science data to be released in order to verify any of these speculations. The images are not sharp enough to see all the details we need to see to tell all of what we are looking at. It also would have been far more interesting if the probe had landed on the "bedrock" area near one of the channels, but you cannot be lucky, like Opportunity, every time you land on a strange planet. Computer software will soon be able to integrate all of the descent imagery and produce an accurate 3-D model of the whole area, up to the resolution limits of the camera, similar to what was done for Endurance and Eagle Craters at the Opportunity site on Mars. All of the other data should eventually give us a much better picture of surface conditions at the landing site.


Posted by apsmith at January 15, 2005 11:48 PM



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