Has Huygens landed next to a stream?

[andersa]

Yes, I see the general shimmer too, but I should clarify that what I'm specifically looking at is the difference in shimmering behaviours of two particular rocks. I can't do as Fridger and send a drawing, but if we take the top-left of these 256?—508 pixel frames as co-ord 0,0, then watch the behaviour of these rocks: they are at co-ords 215, 219 and 217, 245 (i.e., just below the first one). The top rock is flat, muted and darker than the bottom one which looks comparatively white, yet it seems to flicker so much more the white rock which it remarkably steady in all this shimering. Why?

I think this is due to the image compression done onboard Huygens. I have seen no description of the algorithm used (it's not JPEG), but the image is composed of a mosaic of 16x16-pixel squares (they appear as 32x32 in the animated GIF because it has been scaled up from the triplets distributed by the DISR team). Within each square, the sharpness of the image appears to be related to the amount of contrast.

The top rock is found in a pretty "dull" square with little contrast, and if you step through the animation you may see that the quality of the entire square changes significantly. For example, it's rather blurred in frame 66, but sharper in frame 67 (frames are numbered 0-98 by xanim), and the appearance of that rock changes with that.

Such a distinct change could be triggered by any slight shift in overall brightness, or movement of the camera. I think it's little use speculating further without a detailed description of the imaging system, including the compression scheme used.

The white rock below (and the two smaller ones just to the left) are found in a different square, and therefore aren't affected by the same changes. Since that rock is so bright, perhaps it yields sufficient contrast in its square to keep it sharp in the compression process.

The mountain could look smooth due to haze in the distance. I think the upper-right dog-ear is not the same as the lower-left, which is where the flashlight is*. The flashlight fades over time, which is why the white disappears. So, I still think it's a mountain in the background. Current thinking by ESA is that Huygens landed on a flat part within the ridge mountains of the 8km high panorama. I also think that these ridge mountains might turn out to be the Titanian counterpart to Evil Dr. Ganymedes's Ganymedian ridges...

I'll buy the flashlight explanation. However, the upper-right dog-ear is present also in other Huygens images, taken during descent, such as triplet 526. In particular, triplet 202 suggests this is a camera artefact.
http://www.lpl.arizona.edu/%7Ekholso/im ... et.526.jpg
http://www.lpl.arizona.edu/%7Ekholso/im ... et.202.jpg

There may still be a mountain, but as there is no detail, we can't tell whether it's visible from Huygens. It's just a fuzzy horizon to me. Are there any other clues as to what direction Huygens is looking in?

* If you look at the web page showing pictures of the DISR, you'll see they show the flashlight to the right of the cameras. Thus, I think the Huygens pictures are currently mirrored. Oops.

Has there been any attempt at correlating the images taken by Huygens from higher altitude with those taken earlier by Cassini from space (in infrared, I think)? I'd like to think the DISR team can tell left from right in their own imaging system design...

[Spaceman Spiff]

Well, I have to say that the likeliness of a stream flowing has diminished, and with today's release from ESA, this:

Heat generated by Huygens warmed the soil beneath the probe and both the GCMS and SSP detected bursts of methane gas boiled out of surface material, reinforcing methane's principal role in Titan's geology and atmospheric meteorology -- forming clouds and precipitation that erodes and abrades the surface."
(Source:http://www.esa.int/SPECIALS/Cassini-Huygens/SEMHB881Y3E_0.html)

means that there could have been a lot of shimmering due to rising methane gas in front of the camera.

But it does look like Huygens sits next to a dried-out streambed after all then.

Spiff.

[t00fri]

Most of what was communicated today in the press conference makes a lot of sense to me.

It appears that the landscape is indeed basically wet, but not continuously. It's more like in certain desert regions on Earth: mostly dry, but occasionally, torrential rains are falling that temporarily transform the desert into a new kind of florishing landscape with rivers flowers and all that.

In case of Titan, the flowers are clearly missing

But after methane rains the landscape becomes indeed wet with flowing rivers and lakes of methane. Since at -170 degrees centigrade, methane is evaporating fairly rapidly, there will probably be quite a "damp" climate after strong methane rains, until the rivers and lakes will be dry again.

It seems beyond doubt that methane rains and erosion form a substantial element that significantly contributes to shaping Titan's landscape. The crucial role of methane is also confirmed by this intense layer of methane in the atmosphere around 18-20 km altitude. So a methan circuit through weather evolution is most plausible.

Bye Fridger

[chris]

It seems that the surface temperatures and pressures on Titan mean that methane evaporates quite easily--methane phase diagram here:

http://www.astro.upenn.edu/~trilling/te ... 5/ch4.html)

I wonder if this could lead to a cycle in which methane rain falls and fills up low areas as the temperature drops in Titan's 8 Earth-day night, and then evaporates during the day. This might explain why Cassini has not yet observed the specular reflections that you'd expect to see from bodies of liquid--as far as I know, Cassini's close approaches to Titan both occurred from a phase angle of near zero degrees (deliberately, in order get the clearest possible view of the surface through the atmosphere.)

--Chris

[andersa]

I wonder if this could lead to a cycle in which methane rain falls and fills up low areas as the temperature drops in Titan's 8 Earth-day night, and then evaporates during the day.

Would all the methane evaporate completely, or just the smaller lakes (assuming there are larger depressions retaining substantial bodies, if not oceans, of liquid methane throughout the day, in spite of massive evaporation)? That sounds like quite a lot of vapor and liquid being transported up and down every 16 days.

This might explain why Cassini has not yet observed the specular reflections that you'd expect to see from bodies of liquid--as far as I know, Cassini's close approaches to Titan both occurred from a phase angle of near zero degrees (deliberately, in order get the clearest possible view of the surface through the atmosphere.)

I recall that Cassini has had to employ infrared imaging to see through the haze. Would the specular effects be just as visible in that part of the spectrum (I suppose the Sun is equally more distinct as seen from the surface in infrared rather than other wavelengths)?

Depending on how fast the methane evaporates, Cassini would probably have to look near the morning terminator, from the night side towards the Sun.

I thought Cassini would be able to obtain elevation data from Titan using radar. There were some radar measurements shown on the JPL website after the first flyby in October, but they didn't seem to provide much insight. Will we see better results from Cassini later, or will it take another mission to work out the topography of Titan in general, not just the area where Huygens landed?