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RE: Titan
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The Cassini spacecraft carried the European Space Agency's Huygens probe to Saturn and released it in December 2004. The probe landed on Titan Jan. 14, 2005, acquiring a set of images using the descent imager/spectral radiometer camera as it parachuted to the surface.



As Cassini continued to orbit Saturn, its imaging science subsystem and visual and infrared mapping spectrometer mapped the region where the Huygens probe landed. On Friday, Oct. 28, 2005, Cassini's radar instrument provided the highest resolution orbital data yet of this area.


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The two images shown here tell the story. On the left, in colour, is a composite of the imaging camera and infrared data (red areas are brighter and blue darker, as seen in infrared). On the right is the synthetic aperture radar image. The Huygens descent images are shown inset on the left image and outlined in yellow on the right. The magenta cross in both images shows the best estimate of the actual Huygens landing site. This is a preliminary result, based on the best information available at the present time.

In the left image, the brighter areas seen by the Huygens camera correspond to the large area depicted in red and yellow. On closer inspection, bright features within the Huygens mosaic seem to correspond to smaller features in the map composed of data from the visual and infrared spectrometer and imaging camera. On the right, the correspondence is less clear. In radar images bright features are usually rougher, so one would not necessarily expect an obvious connection.

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Titan clouds
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University of Arizona scientists say that the peculiar clouds at middle latitudes in Titan's southern hemisphere may form in the same way as distinct bands of clouds form at Earth's equator.

"Titan's weather is very different from Earth's. If you walked past Titan's minus-40-degree-latitude line, you might be showered with liquid natural gas. If you decided to visit Titan's south pole, you might encounter a storm the size of a hurricane which also consists of methane, more commonly known as natural gas. Otherwise, don't expect clouds on Titan." - UA associate professor Caitlin Griffith.

Titan's weather forecast has remained the same for years, and that baffles scientists. They don't understand why clouds a thousand miles long stretch over the temperate latitude.

"Imagine how curious it would be if beyond Earth's poles, clouds existed only at the latitude that crosses New Zealand, Argentina and Chile. Furthermore, Henry Roe (of the California Institute of Technology) and his colleagues find that most of these peculiar clouds bunch up at zero degrees and 90 degrees longitude, analogous to Earth longitudes southwest and southeast of the Cape of Good Hope" - Caitlin Griffith.


These false colour images show evidence of changing weather patterns in the skies over Titan's southern hemisphere. Cassini's visual and infrared mapping spectrometer took the images during two recent flybys. In the first image (left), taken Oct. 26, 2004, Titan's skies are cloud-free except for a patch of clouds over the south pole near the bottom of the image. In contrast the image at right, taken Dec. 13, 2004, shows extensive patches of clouds formed over temperate latitudes.
(Photo: University of Arizona/JPL/NASA)



The highly localised nature of the clouds suggests that they have something to do with Titan's surface. Scientists think ice volcanoes must be venting methane -- the gas that condenses as clouds -- into Titan's hazy, mostly nitrogen atmosphere. Otherwise, the moon's atmospheric methane would have vanished billions of years ago because methane is destroyed by ultraviolet sunlight.

Griffith, Paulo Penteado and Robert Kursinski of UA's Lunar and Planetary Lab studied the origin of the clouds by analyzing cloud height and thickness using images from Cassini's visual and infrared mapping spectrometer (VIMS). This instrument is among a suite of instruments on the Cassini spacecraft orbiting Saturn. It measures light at 256 different wavelengths. Griffith is a member of the UA-based VIMS team, headed by Robert Brown of UA's Lunar and Planetary Lab. Griffith and her colleagues analysed images that gave them a 3-D view of the cloud and a six-frame movie that shows how it evolved over three hours.

"The structure of the clouds turns out to be complicated. We detected not one region, but many regions of cloud formation. Each long cloud consists of a number of vigorous storms where clouds rise to 40 kilometres altitude in a couple of hours and dissipate in the next half hour. The rate of cloud ascent and dissipation suggests that we are witnessing the formation of convective clouds, likely similar to thunderstorms, that disappear through rainfall.
Over the next several hours we see the clouds form long tails, indicating that strong westerly winds stretch out the clouds and carry the particles downwind a thousand kilometres. This detailed look into the structure of these clouds reveals that the clouds evolve from a number of small active cloud formation centres lined up like an uneven string of beads long 40 degrees south latitude. These localized storms cause a healthy rain, and very long clouds, once the wind has stretched them out
" -Caitlin Griffith.

Griffith argues that it's improbable that many ice volcanoes, all aligned at 40 degrees south latitude, and are forming these clouds. In addition, the scientists estimate that the cloud activity at zero degrees longitude, if volcanic, does not appear to spew out enough methane to create the mid-latitude cloud band. Smaller clouds actually lie upwind of the main cloud at zero degrees longitude, they note. The team also conclude that the clouds aren't obviously caused by Saturn's tidal pull on Titan's atmosphere. They also don't find evidence that mountains and lakes might cause mountain clouds or marine clouds.

"We believe that it's no coincidence that Titan's south polar cap of smog extends from the pole to 40 degrees south latitude -- exactly where the methane cloud band appears" - Caitlin Griffith.
The researchers suggest that global circulation may cause the air to rise at this latitude on Titan, much as clouds form in a band around the Earth's equator and rain on the Caribbean islands.
"Such rising air would cut off air from the south polar region from mixing with the rest of the moon's atmosphere, causing smog to build up and form a cap over the pole" - Caitlin Griffith.

Theoretical modelling supports the UA team's conclusion. Pascal Ranou and his group in Paris studied Titan's circulation with an elaborate and complicated general circulation model. His model predicts that solar heating naturally creates rising air on Titan at 40 degrees south latitude.

The next mystery is why Titan's southern mid-latitude clouds are bunched at zero degrees longitude. There's no evidence yet that volcanoes, mountain ranges or Saturn's tides are involved.
"What's causing the bunching is unclear, and likely involves unknown features on Titan's still largely unexplored surface" - Caitlin Griffith.

Griffith, Kursinki and Penteado are publishing an article on their research in the Oct. 21 issue of Science.

source

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Posts: 131433
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RE: Titan
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Fluids have flowed and cut these deeply-incised channels into the icy surface of Titan as seen in this Synthetic Aperture Radar image. The channels are roughly 1 kilometre across and perhaps 200 meters deep; some can be traced as far as 200 kilometres. Many of them have angular segments suggesting they may follow faults in Titan's crust.


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Taken together with the two other radar passes (October 2004 and February 2005), these very high resolution images have identified at least two distinct types of drainage and channel formation on Titan. The style shown in this image consists of long valleys following angular patterns without many tributaries, suggesting that fluids flow over great distances. By contrast, the previous images show channels that form a denser network that might indicate rainfall.
The area is located at about 55 degrees south latitude, 7.5 degrees west longitude and extends over 300 kilometres right to left.

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A portion from a radar swath centred on 66 degrees South, 356 West in central Mezzoramia. This portion shows a possible shoreline in the central part of the dark albedo feature known as Mezzoramia.
On the left, the terrain that is suggestive of erosion by liquids, with alcoves and scarps. At right, the surface is quite dark suggesting that the area is much smoother than any other place so far looked on Titan by Cassini RADAR. Many of the bright features that bound this terrain are similar to shoreline terrain on Earth.

This portion is 330 km wide and 175 km tall.


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This portion is near the very end of the SAR swath data that was recovered. The second half was lost.


This Cassini Synthetic Aperture Radar image of Titan was taken on Sept. 7, 2005, at a distance of 2,000 kilometres from Titan.
This portion is from south central Tsegihi near 48 degrees South, 14 degrees West. This view extends 240 kilometres from left to right. At the top is a deeply incised channel flowing from a region of bright, rough terrain down to darker, smoother material.


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Near the bottom of the image is a branching network of channels. These properties are suggestive of rainfall run-off channels rather than river networks.

The channels are deeply incised, suggesting either that the liquid efficiently erodes the bedrock, or these channels have been active for a good percentage of geologic time.

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Fensal-Aztlan
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This mosaic of the Fensal-Aztlan (formerly known as the "H") region on Titan, taken during last week's Titan flyby, is just 4 frames within a larger, 20-frame mosaic to be released later.


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Fensal is the northern branch of the "H". Fensal has some subtle brightness variations and has quite a few bright spots, or "islands", dotting the region, ranging in size from 5 to 40 kilometres across. Their distribution appears to be more scattered than similar sized bright spots in Shangri-la, west of Xanadu.
These landforms currently are thought to be water ice upland areas, surrounded by shallower terrain that is filled-in with dark particulate material from the atmosphere. A few larger islands are also seen, like Bazaruto Facula (near right, containing a dark crater), and several islands in western Fensal. When viewed in images of Shangri-La (on the other side of Titan), island-like landforms of this size tend to occur in clusters with apparent preferred orientations.

The spots are clustered into several "archipelagos" and aligned in a similar fashion, usually east-west. The spots in Fensal don't seem to have a preferred orientation. A few larger bright spots can be seen in Fensal, including Bazaruto Facula on its eastern end.

Aztlan, the southern branch of the H plus the dark region surrounding Elba Facula to the east (not in this particular crop), has far fewer smaller islands, but does have several large islands, including Sotra Facula, a 240 by 120 km sized bright feature just right of centre in the lower left frame, and Coats Facula, a smaller island to the east of Sotra.

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Titan Flyby7
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Bad news about Titan flyby number 7.
There appears to have been a software glitch with one of the solid-state recorders. Apparently, a bit was switched earlier this week telling the recorder not to accept any commands to record data.
So it appears that no data was recorded after 12 minutes prior to closest approach, causing the loss of nearly all the RADAR SAR data (and the second altimetry pass), and all the ISS, UVIS, and VIMS data from after closest approach. Another problem, during playback yesterday, may have caused the loss of the COMBINED mosaic (and the RADAR data that was recorded).


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RE: methane monsoon
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Brief but powerful monsoons of liquid methane may lash parts of Saturn's giant moon Titan every few hundred years; suggest new calculations based on observations with the Cassini spacecraft. Astronomers also think they have observed thunderstorms growing and raining down on the moon.

Methane makes up about 5% of the Titanís thick atmosphere and is thought to rain down to the surface and then evaporates back into clouds in a cycle similar to the water-cycle on Earth.

Observations with both the Cassini spacecraft in orbit around Saturn and the Huygens probe sent down to Titan in January 2005 seem to bear this out. They show dark, river-like channels carved into higher, lighter terrain and a round feature resembling a lake near the South Pole.
But so far scientists have not been able to prove that liquid methane flows through these features today.

"Everything looks pretty fresh on Titan. It's akin to seeing riverbeds that don't have water in them, and knowing there was rain in the last season." - Jonathan Lunine, planetary scientist at the University of Arizona in Tucson, US.

Now, University of Arizona colleague Ralph Lorenz says Titan may well experience short, periodic downpours like those in deserts in the south-west US Ė though much more intense. Lorenz presented the "methane monsoon" theory Ė named after an Arthur C Clarke novel in which astronauts get blown away by a methane storm Ė on Thursday at a planetary sciences meeting in Cambridge, UK.

The evidence comes from imaging radar data from the Cassini spacecraft. These reveal canyon-like features that end in triangular slopes that appear to be littered with cobbles a few centimetres wide.
That may indicate flash flooding, says colleague Jason Barnes. He says most sediment transport in rivers on Earth occurs during the "peak discharge" of such events.

"So if you a river jumps to ten times its normal level, like the Colorado River through the Grand Canyon, most sediment is transported during the three days of the flood".

The radar also shows sinuous shapes resembling rivers that only branch off in a few places. The curviness, size, and number of branching resemble channels in Earth's deserts that are carved in heavy bursts of rainfall that quickly seep into the porous soil.

"The shapes of river channels on Titan resemble those we see in the desert southwest. Where I live in Tucson, you see river channels and there's water in them for two or three days a year and it's dry the rest of the time" - Ralph Lorenz.

It may be raining somewhere on Titan at any given time, but that centuries may pass between rainstorms in a particular region. Sunlight drives the rain-evaporation cycle, and models of Titan's haze, reflectivity, and temperature suggest the Sun can only produce an average of about a centimetre or two of rain per year over all of Titan.

"That doesn't say whether it's a millimetre every month, a centimetre every year, or several metres every thousand years" - Ralph Lorenz.

But if the methane in Titan's atmosphere were concentrated into a single liquid layer, it would cover the entire moon in a blanket 10 metres thick.

"The air is holding a lot of methane" - Jason Barnes.

So if it rains less often, it dumps more liquid Ė perhaps as much as a metre - at a time.
Whether or not these episodic methane monsoons occur, Cassini scientists believe they have now seen evidence for methane rain on the moon.
Using the spacecraft's visual infrared mapping spectrometer (VIMS), they have studied the evolution in height and thickness of long clouds that tend to cluster around the moon's mid-southern latitudes.
The team observed "vigorous centres" in the clouds as they rose from a height of 23 kilometres to 44 km at speeds of several tens of metres per second. Then, the cloud tops dissipated or fell 10 kilometres over the next 30 minutes.
This suggests the clouds "evolve convectively and dissipate through rain" - Caitlin Griffith, University of Arizona.

All of the recent Titan observations, including the detection of a limited amount of liquid methane just under the surface where Huygens landed, point to "an active hydrological cycle. It's more similar to Earth than you might think"- Jason Barnes.

The research was presented at a meeting of the American Astronomical Society's Division of Planetary Sciences in Cambridge, UK

Source

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Posts: 131433
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RE: Titan
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This is one of the first images returned from Cassini during the eight Titan flyby.
The image was taken on Sept. 6, 2005 and received on Earth Sept. 8, 2005.



The camera was pointing toward Titan that was approximately 184,213 kilometres away. The image was taken using the CB3 and CL2 filters.


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RE: Titan September flyby
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This image was taken on September 06, 2005 and received on Earth September 08, 2005. TITAN was approximately 205,002 kilometres away. The image was taken using the CL1 and CB3 filters.

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Shiwanni Virgae (at top) and central Tsegihi

This image was taken on September 06, 2005 and received on Earth September 08, 2005. TITAN was approximately 198,075 kilometres away. The image was taken using the CL1 and CB3 filters.

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Bazaruto Facula (with an 80-km crater at its center) at upper right. Quivira at bottom.

This image was taken on September 06, 2005 and received on Earth September 08, 2005. TITAN was approximately 196,345 kilometres away. The image was taken using the CL1 and CB3 filters.

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Strait between Fensal and Aztlan, Sotra Facula (just right of center), and western Aztlan

This image was taken on September 06, 2005 and received on Earth September 08, 2005. TITAN was approximately 191,850 kilometres away. The image was taken using the CL1 and CB3 filters.

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Islands in central Fensal

This image was taken on September 06, 2005 and received on Earth September 08, 2005. TITAN was approximately 189,432 kilometres away. The image was taken using the CL1 and CB3 filters.

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Omacatl Macula (just left of center) and the northern boundary of Fensal (Elpis Macula at upper right)

-- Edited by Blobrana at 01:33, 2005-09-11

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RE: Titan flyby
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This map of Titan's surface illustrates the regions that will be imaged by Cassini during the spacecraft's close flyby of Titan on Sept. 7, 2005. At closest approach, the spacecraft is expected to pass approximately 1,075 kilometres above the moon's surface.
This is Cassini's eighth flyby of Titan out of 45 flybys planned in the four-year tour.


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The coloured lines delineate the regions that will be imaged at differing resolutions.
Zooming-in closer to Titan than during its previous pass two weeks earlier, Cassini camera coverage again focuses on the region known informally as "the H". Some of the narrow-angle camera images Cassini takes during this close flyby will be composited into high-resolution mosaics.

This encounter also should provide an excellent view of Bazaruto Facula and its central 80-kilometer-wide crater.

The map shows only brightness variations on Titan's surface (the illumination is such that there are no shadows and no shading due to topographic variations). Previous observations indicate that due to Titan's thick, hazy atmosphere, the sizes of surface features that can be resolved are a few to five times larger than the actual pixel scale labelled on the map.

The images for this global map were obtained using a narrow band filter centred at 938 nanometres - a near-infrared wavelength at which light can penetrate Titan's atmosphere to reach the surface and return through the atmosphere to be detected by the camera.
The images have been processed to enhance surface details.

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