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TOPIC: Titan


L

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RE: Titan map
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This global infrared map of Titan was composed with data taken during the last two Titan flybys, on Dec. 26, 2005, and Jan. 15, 2006.

Cassini's visual and infrared mapping spectrometer map was constructed from false-colour images taken at wavelengths of 1.6 microns shown in blue, 2.01 microns in green, and 5 microns in red. All three images are of reflected sunlight.
The viewing geometry of the December flyby is roughly on the opposite hemisphere of the flyby in January.


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Titan has two bright regions, the large one known as Tui Reggio, located at approximately 25 degrees south latitude and 130 degrees west longitude, and the other as Hotei Arcus, at 20 degrees south latitude and 80 degrees west longitude. These regions are thought to be surface deposits, probably of volcanic origin, and may be water and/or carbon dioxide frozen from the volcanic vapour.
The western margins of Tui Reggio have a complex flow-like structure consistent with eruptive phenomena. The reddish feature at the south pole is Titan's south polar cloud system, which was very bright during the December flyby.
The globe of Titan exhibits two major types of terrain, one is very bright, and a darker one seems to be concentrated near the equator.
The impact crater Sinlap is visible at approximately latitude 13 degrees north and longitude 16 degrees west. The unresolved regions between longitudes of 30 degrees and 150 degrees east will be filled in during subsequent flybys.

Other Titan maps

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This mosaic was taken on Dec. 26, 2005.
North is at the top.



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These three mosaics were composed with data from Cassini's visual and infrared mapping spectrometer taken during the last three Titan flybys, on Oct. 28, 2005 (top image), Dec. 26, 2005 (middle image), and Jan. 15, 2006 (bottom image).

These false-colour images were constructed from images taken at the following wavelengths: 1.6 microns (blue), 2.01 (green), and 5 microns (red).


Credit: NASA/JPL/University of Arizona

The viewing geometry of the December flyby is roughly on Titan's opposite hemisphere from the flybys in October and January. There are several important features to note in the images. The first is that the south polar cloud system (on left) was very bright during the December flyby, while during the October and January flybys, it is barely visible, indicating that the atmosphere over Titan's south pole is very dynamic.

In the December (middle) mosaic, a north polar hood (right) that is bright at 5 microns is visible. Its composition is unknown. The north polar hood is barely seen in the October (top image) and January (bottom image) data. Visible in the October and December images just south of the equator is Tui Reggio, a region nicknamed the "chevron." This region is very bright at 5 microns and is among the brightest features on Titan at that wavelength.
Tui Reggio is thought to be a surface deposit, probably of volcanic origin, and may be water and/or carbon dioxide frozen from the vapour. The December flyby data show that the western margins of Tui Reggio have a complex flow-like character consistent with eruptive phenomena.

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Using recent Cassini, Huygens and Earth-based observations, scientists have been able to create a computer model which explains the formation of several types of ethane and methane clouds on Titan.

Clouds have been observed recently on Titan, Saturn’s largest moon, through the thick haze, using near-infrared spectroscopy and images of the South Pole and temperate regions near 40° South. Recent observations from Earth-based telescopes and the NASA/ESA/ASI Cassini spacecraft are now providing an insight into cloud climatology.
A European team, led by Pascal Rannou of the Service d’Aeronomie, IPSL Universite de Versailles-St-Quentin, France, has developed a general circulation model which couples dynamics, haze and cloud physics to study Titan climate and enables us to understand how the major cloud features which are observed, are produced.
This climate model also allows scientists to predict the cloud distribution for the complete Titan year (30 terrestrial years), and especially in the next years of Cassini observations.
The Voyager missions of the early 1980s gave the first indications of condensate clouds on Titan. Because of the cold temperatures in the moon’s atmosphere (tropopause), it was assumed that most of the organic chemicals formed in the upper atmosphere by photochemistry would condense into clouds while sinking. Methane would also condense at high altitudes, it was believed, having been transported from the surface.
Since then, several one-dimensional models of Titan’s atmosphere including sophisticated microphysics models were created to predict the formation of drops of ethane and methane. Similarly, the methane cycle had been studied separately in a circulation model, but without cloud microphysics.
These studies generally found that methane clouds could be triggered when air parcels cooled while moving upward or from equator to pole. However, these models hardly captured the fine details of the methane and ethane cloud cycles.
What Rannou’s team has done is to combine a cloud microphysical model into a general circulation model. The team can now identify and explain the formation of several types of ethane and methane clouds, including the south polar and sporadic clouds in the temperate regions, especially at 40° S in the summer hemisphere.
The scientists found that the predicted physical properties of the clouds in their model matched well with recent observations. Methane clouds that have been observed to date appear in locations where ascending air motions are predicted in their model.
The observed south polar cloud appears at the top of a particular ‘Hadley cell’, or mass of vertically circulating air, exactly where predicted at the south pole at an altitude of around 20-30 kilometres.
The recurrent large zonal (longitudinal direction) clouds at 40° S and the linear and discrete clouds that appear in the lower latitudes are also correlated with the ascending part of similar circulation cell in the troposphere, whereas smaller clouds at low latitudes, similar to the linear and discrete clouds already observed by Cassini are rather produced by mixing processes.

"Clouds in our circulation model are necessarily simplified relative to the real clouds, however the main cloud features predicted find a counterpart in reality. Consistently, our model produces clouds at places where clouds are actually observed, but it also predicts clouds that have not, or not yet, been observed" - Pascal Rannou.

Titan’s cloud pattern appears to be similar to that of the main cloud patterns on Earth and Mars. The puzzling clouds at 40° S are produced by the ascending branch of a Hadley cell, exactly like tropical clouds are in the Intertropical Convergence Zone (ITCZ), as on Earth and Mars.
Polar clouds - produced by 'polar cells' - are similar to those produced at mid-latitudes on Earth. On other hand, clouds only appear at some longitudes. This is a specific feature of Titan clouds, and may be due to a Saturn tidal effect. The dynamical origin of cloud distribution on Titan is easy to test.
Cloudiness prediction for the coming years will be compared to observations made by Cassini and ground-based telescopes. Specific events will definitely prove the role of the circulation on the cloud distribution.

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This image of Titan was taken by the Cassini spacecraft on January 15, 2006 when it was approximately 25,495 kilometres away. The image was taken using the CB3 and CL2 filters.


Image Credit: NASA/JPL/Space Science Institute

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The Cassini spacecraft took this image of Titan on January 15, 2006, when it was approximately 16,953 kilometres away. The image was taken using the CL1 and MT1 filters.



The Cassini spacecraft took this image of Titan on January 16, 2006, when it was approximately 26,172 kilometres away. The image was taken using the CL1 and CB3 filters.

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Titan T10
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This image of Titan was taken on the T10 flyby on January 13, 2006, by the Cassini spacecraft when it as approximately 1,257,518 kilometres away. The image was taken using the IRP0 and CB3 filters.


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Titan Halo
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Images taken by the Cassini space probe using blue, green and red spectral filters were used combined to create this enhanced-colour view.
The images in this view were taken by the Cassini narrow-angle camera on May 5, 2005, at a distance of approximately 1.4 million kilometres from Titan and at a sun-Titan-spacecraft, or phase, angle of 137 degrees.
Image scale is 8 kilometres per pixel.



The colour images were combined with an ultraviolet view that show up a high-altitude, detached layer of haze. The ultraviolet part of the composite image was given a blue hue to match the bluish colour of the upper atmospheric haze seen in visible light.
Small particles that populate high hazes in Titan's atmosphere scatter short wavelengths more efficiently than longer visible or infrared wavelengths, so the best possible observations of the detached layer are made in ultraviolet light.

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Titan Dec 26 flyby
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This image was taken on December 26, 2005 and received on Earth December 27, 2005. Titan was approximately 13,355 kilometres away, and the image was taken using the CB3 and CL2 filters.



This image was taken on December 26, 2005 and received on Earth December 27, 2005. Titan was approximately 15,438 kilometres away, and the image was taken using the CL1 and IR1 filters.



This image was taken on December 26, 2005 and received on Earth December 27, 2005. Titan was approximately 29,360 kilometres away, and the image was taken using the CB3 and CL2 filters.

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This image was taken on December 26, 2005 and received on Earth December 27, 2005 Titan was approximately 58,156 kilometres away, and the image was taken using the CB3 and CL2 filters.

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This image was taken on December 26, 2005 and received on Earth December 27, 2005. Titan was approximately 109,931 kilometres away, and the image was taken using the CL1 and CB3 filters.

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Huygens probe
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On 14 January 2005, ESA's Huygens probe revealed an extraordinary world, resembling Earth in many respects, especially in meteorology, geomorphology and fluvial activity.

audio interview (mp3)

Unique results from the Aerosol Collector and Pyrolyser (ACP) and the Gas Chromatograph Mass Spectrometer (GCMS) have given scientists their first in situ chemical data on Titan's atmosphere, including aerosols, chemical composition and isotopes.



Two of Titan's key unknowns are the origin of the molecular nitrogen and methane in the atmosphere, and the mechanisms by which methane is maintained in the face of rapid destruction by photochemistry (chemical processes that are accompanied by or catalysed by the emission or absorption of visible or ultraviolet light).

The GCMS measured chemical composition and isotope abundances from 140 km altitude to the surface and confirmed the primary constituents were nitrogen and methane, and that the haze in the atmosphere is primarily methane.

From isotopic ratio measurements, the Huygens scientists obtained two key findings. The carbon isotope ratio (12C/13C) measured in methane suggests a continuous or periodic replenishment of methane in the atmosphere, but no evidence was found of active biological systems.

The nitrogen isotope ratio (14N/15N) suggests to the scientists that the early atmosphere of Titan was five times denser than it is now, and hence lost nitrogen to space.

Argon 36 was detected for the first time, but not xenon or krypton. However, the argon was found in low abundance, which is especially interesting because of the huge, nitrogen-dominated atmosphere and because about 50% of the mass of Titan is water ice, known to be a potentially efficient carrier of noble gases.

This low abundance implies the atmosphere was condensed or captured as ammonia, instead of nitrogen. The non-detection of the other noble gases, a surprising finding, will also fuel theories of the origin and evolution of Titan's atmosphere.


Shows the total measured mass spectrum on the Titan surface with the signature of several compounds.
Credits: ESA/NASA/GSFC/ASI/GCMS Team


The composition of surface vapours obtained by GCMS after landing shows that Huygens landed on a surface wet with methane, which evaporated as the cold soil was heated by the warmer probe. The surface was also rich in organic compounds not seen in the atmosphere, for example cyanogen and ethane, indicating a complex chemistry on Titan's surface as well as in the atmosphere.

Argon 40 was also detected at the surface and its presence indicates that Titan has experienced in the past, and is most likely still experiencing today, internal geological activity.
Titan's aerosols play an important role in determining atmospheric thermal structure, affecting the processes of radiative heating and cooling. They can help to create warm and cold layers that in turn contribute to circulation patterns and determine the strengths of winds.


Shows the increase of Nitrogen and Methane during the Probe descent and the rapid and important increase in Methane at the surface.
Credits: ESA/NASA/GSFC/ASI/GCMS Team


The ACP obtained direct measurements of the chemical make-up of these aerosol particles. From an analysis of the products obtained by pyrolysis (chemical decomposition of organic materials by heating) of aerosols at 600°C, ammonia and hydrogen cyanide were the first molecules identified.

This is of prime importance because ammonia is not present as a gas in the atmosphere, hence the aerosols must include the results of chemical reactions that may have produced complex organic molecules. They are not simply condensates.

Aerosol particles may also act as condensation nuclei for cloud formation, and are the end-products of a complex organic chemistry which is important in astrobiology. Indeed, Titan offers the possibility to observe chemical pathways involving molecules that may have been the building blocks of life on Earth.

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