Titan 'T28' Mosaic
May 22, 2007

Bright and dark terrains on Titan's trailing hemisphere are revealed by Cassini's Imaging Science Subsystem in this mosaic of images taken during the T28 flyby in April 2007.

The region shown in this image, centered on the northern part of Titan's trailing hemisphere (near 31.2 degrees North, 220.7 degrees West), had only been seen at very low resolution until February 2007, when Cassini flew over this area for the first time. This mosaic consists of images taken during one of a series of flybys in early 2007 designed to study this long unavailable part of Titan (5,150 kilometers, or 3,200 miles across).

Several intriguing surface features can be seen in this mosaic that warrant further study. Along the top of the mosaic is a series of dark lineaments, or linear features, that stand out against the blandness of the northern, mid-latitude terrain. These features were also observed by the RADAR instrument in December 2006 and represent an area of potential future co-analysis for the RADAR and camera teams. Another such region is the large bright area known as Adiri at bottom center, also imaged by RADAR in October 2005.

The mosaic shows a number of dark areas within Adiri that line up with small dune fields observed by RADAR. A portion of the dark terrain surrounding Adiri was also observed in 2005 by RADAR, and likewise was found to consist of large stretches of longitudinal dune fields --further supporting the correlation between equatorial dark regions and dune "seas."

To the east of Adiri is a dark spot surrounded by a ring of bright material, which may be associated with an impact crater similar to Sinlap, discovered earlier in the Cassini mission (see Titan Mosaic - East of Xanadu).

This mosaic consists of 29 separate frames using a total of 116 images. Each frame consists of three images, taken using a filter sensitive to near-infrared light centered at 938 nanometers, allowing for observations of Titan's surface and lower atmosphere, added together. An image taken using a filter sensitive to visible light centered at 619 nanometers was then subtracted from the product, effectively removing the lower atmosphere contribution to the brightness values in the image, increasing image contrast and improving the visibility of surface features. This process is also intended to reduce noise, but some camera artifacts still remain, such as a dark ring caused by dust in the camera system near the bottom right of each frame.

For a wide angle view taken during this Titan encounter, see Titan 'T28' View.

The images used for this mosaic were taken on April 11, 2007 from distances ranging from 106,000 to 180,000 kilometers (66,000 to 112,000 miles). This mosaic is in an orthographic projection with a pixel scale of 1.5 kilometers (0.9 miles) per pixel, although the size of resolvable features is likely several times larger, due to atmospheric scattering. An orthographic view is most like the view seen by a distant observer looking through a telescope.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Coasts and Drowned Mountains
May 23, 2007

On May 12, 2007, Cassini completed its 31st flyby of Saturn's moon Titan, which the team calls T30. The radar instrument obtained this image showing the coastline and numerous island groups of a portion of a large sea, consistent with the larger sea seen by the Cassini imaging instrument (See Seeing Farther North).

Like other bodies of liquid seen on Titan, this feature reveals channels, islands, bays, and other features typical of terrestrial coastlines, and the liquid, most likely a combination of methane and ethane, appears very dark to the radar instrument. What is striking about this portion of the sea compared to other liquid bodies on Titan is the relative absence of brighter regions within it, suggesting that the depth of the liquid here exceeds tens of meters (tens of yards). Of particular note is the presence of isolated islands, which follow the same direction as the peninsula to their lower right, suggesting that they may be part of a mountain ridgeline that has been flooded. This is analogous to, for example, Catalina Island off the coast of Southern California.

The image as shown is about 160 kilometers (100 miles) by 270 kilometers (170 miles) at 300-meter (980-foot) resolution. The image is centered near 70 degrees north latitude and 310 west longitude.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/home/index.cfm.

Credit: NASA/JPL

Source: NASA/JPL - Cassini

High Altitude Hints
June 1, 2007

The Cassini spacecraft catches a glimpse of features that reveal important clues about processes occurring in Titan's atmosphere.

The north polar stratosphere exhibits a banded appearance, as fast-moving clouds whirl around the giant moon. The moon's halo -- its detached, high-altitude global haze layer -- is faintly visible here as well.

Planet-sized Titan is 5,150 kilometers (3,200 miles) across. The image was taken with the Cassini spacecraft narrow-angle camera using a combination of spectral filters sensitive to wavelengths of polarized ultraviolet light. The image was obtained on May 15, 2007 at a distance of approximately 1.3 million kilometers (800,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 25 degrees. Image scale is 15 kilometers (10 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

1 June 2007

This composite was produced from images returned on 14 January 2005, by ESA's Huygens probe during its successful descent to land on Titan. It shows the boundary between the lighter-coloured uplifted terrain, marked with what appear to be drainage channels, and darker lower areas. These images were taken from an altitude of about 8 kilometres with a resolution of about 20 metres per pixel.

Credits: ESA/NASA/JPL/University of Arizona

Today, two and a half years after the historic landing of ESA’s Huygens probe on Titan, a new set of results on Saturn’s largest moon is ready to be presented. Titan, as seen through the eyes of Huygens still holds exciting surprises, scientists say.

On 14 January 2005, after a seven-year voyage on board the NASA/ESA/ASI Cassini spacecraft, ESA’s Huygens probe spent 2 hours and 28 minutes descending by parachute to land on Titan. It then sent transmissions from the surface for another seventy minutes before Cassini moved out of range.

On 8 December that year, a combined force of scientists published their preliminary findings in Nature. Now, after another year and a half of patient work, they are ready to add fresh details to their picture of Titan. This time, the papers are published in a special issue of the Planetary and Space Science magazine.

“The added value comes from computer modelling,” says Jonathan Lunine, Huygens Interdisciplinary Scientist from the Lunar and Planetary Laboratory, University of Arizona.

This composite of Huygens DISR images shows patterns of drainage, flow and erosion in the Huygens landing site region.

The top panel shows two types of drainage networks in the bright region about 5-10 kilometres north of the landing site. The lower-left panel is a high-resolution view of the erosional channels around the landing site. The lower right panel is a medium-resolution view of bright ridges standing above the dark plains carved by surface flows.

Credits: ESA/NASA/JPL/University of Arizona

By driving their computer models of Titan to match the data returned from the probe, planetary scientists can now visualise Titan as a working world. “Even though we have only four hours of data, it is so rich that after two years of work we have yet to retrieve all the information it contains,” says François Raulin, Huygens Interdisciplinary Scientist, at the Laboratoire de Physique et Chimie de l'Environnement, Paris.

The new details add greatly to the picture of Saturn’s largest moon. “Titan is a world very similar to the Earth in many respects,” says Jean-Pierre Lebreton, ESA Huygens Project Scientist.

Huygens found that the atmosphere was hazier than expected because of the presence of dust particles – called ‘aerosols’. Now, scientists are learning how to interpret their analysis of these aerosols, thanks to a special chamber that simulates Titan’s atmosphere.

When the probe dropped below 40 kilometres in altitude, the haze cleared and the cameras were able to take their first distinct images of the surface. They revealed an extraordinary landscape showing strong evidence that a liquid, possibly methane, has flowed on the surface, causing erosion. Now, images from Cassini are being coupled with the ‘ground truth’ from Huygens to investigate how conditions on Titan carved out this landscape.

This image of Titan’s surface, obtained by Huygens’ DISR imager, shows patterns of tectonic and fluid-flow activity. The tectonic patterns are indicated by blue lines; the drainage divide is indicated by the red line; flow directions are indicated by the green arrows. The Huygens landing site is marked by a white cross.

Credits: ESA/NASA/JPL/University of Arizona

As the probe descended, Titan’s winds carried it over the surface. A new model of the atmosphere, based on the winds, reveals that Titan’s atmosphere is a giant conveyor belt, circulating its gas from the south pole to the north pole and back again.

Also, the tentative detection of an extremely low frequency (ELF) radio wave has planetary scientists equally excited. If they confirm that it is a natural phenomenon, it will give them a way to probe into the moon’s subsurface, perhaps revealing an underground ocean.

The journey Huygens took to the surface is the subject of the most intense scrutiny, with many papers on the subject. When an anomaly onboard Cassini robbed scientists of data from the Doppler Wind Experiment (DWE), it was followed by a painstaking analysis of data collected by radio telescopes on Earth that were tracking Huygens. Engineers and scientists succeeded in recovering the movement of the probe, providing an accurate wind profile and helping them place some of the images and data from Huygens into their correct context.

Now corroborating evidence, resulting from a thorough analysis of many instruments and engineering sensors on Huygens, is adding unprecedented detail to the movement of the probe during its descent.

And there is still more science to come. “There are so many papers dealing with the results from Huygens that we could not prepare all of them in time for this issue. So a second special issue is already in preparation,” says Raulin.


Notes

This article is an introduction to the series of results to appear in a special issue of the Planetary and Space Science magazine dedicated to results from Huygens. It is based on the paper: 'A new image of Titan – preface to the PPS Special Issue: ‘Titan as seen from Huygens’’, by F. Raulin, M.C. Gazeau and J.P. Lebreton.

Cassini-Huygens is a joint mission between NASA, ESA and the Italian Space Agency (ASI).


For more information

Jean-Pierre Lebreton, ESA Huygens Project Scientist
Email: Jean.Pierre.Lebreton @ esa.int

Jonathan Lunine, Huygens Interdisciplinary Scientist, Lunar and Planetary Laboratory, University of Arizona, USA
Email: Jlunine @ lpl.arizona.edu

Ralph Raulin, Huygens Interdisciplinary Scientist, Laboratoire de Physique et Chimie de l'Environnement, Paris, France
Email: Raulin @ lisa.univ-paris12.fr

Source: ESA - Cassini-Huygens - News

1 June 2007

This image mosaic, covering an area of 120 by 160 kilometres, was obtained thanks to the images taken by Descent Imager and Spectral Radiometer (DISR) on board Huygens, and provides the complete coverage of Titan obtained by DISR. The coverage extends out well beyond the nearest dark dunes (indicated by the arrows) located about 30 kilometres north of the landing site and later imaged by Cassini’s radar.

Credits: ESA/NASA/JPL/University of Arizona

During its two and a half hour descent, the cameras on Huygens showed eager scientists on Earth spectacular regions of bright highlands with river drainages and canyons, bounded by dark plains on Titan. New information about the composition of the landing region is now ready for the public.

Since the mission, planetary scientists have been using the Radar System and the Visible and Infrared Mapping Spectrometer (VIMS), on board the orbiting Cassini spacecraft to investigate the composition of the region Huygens flew over.

Before Huygens, Titan’s surface was a total mystery. The reason was simple: it was covered by a very opaque haze. As the probe penetrated the layer of haze within the atmosphere, “Huygens revealed a previously invisible world,” says Jean-Pierre Lebreton, ESA’s Huygens Project Scientist.

Laurence Soderblom, US Geological Survey, has been trying to make sense out of what Huygens saw. Surprisingly, one of the things that proved unexpectedly difficult was locating the Huygens landing site on the images from Cassini. “When we looked at the SAR images (Synthetic Aperture Radar) and compared them to the VIMS data, we saw little correlation,” reveals Soderblom.

This image of the Huygens landing region is composed of a special mosaic of the best images obtained by the Huygens’ DISR instrument, overlaid on Cassini’s SAR radar images (top) and on a Cassini’s VIMS image of the area (bottom).

In the top image, the landing site is located at about 30 kilometres south of the nearest dunes, visible as stripes at the top of the image.

In the bottom image, the bright feature on the background could be explained as fine-grained, water-free dust deposits from the atmosphere. These may have been washed out by methane rivers and floods in some areas, exposing a water-ice rich substrate visible in blue in the image.

Credits: ESA/NASA/JPL/University of Arizona

The boundary between the bright highlands and dark plains that Huygens drifted over simply did not show up in the radar images. Finally, the clue came in the form of two isolated dark sands dunes about 30 kilometres north of the landing site visible in both SAR and Huygens’ images. They are probably composed of sugar-size hydrocarbon grains between 100 and 300 microns in diameter.

Most of Titan’s dunes are giants, each one stretching for up to 100 kilometres in length across the dark plains and separated by 10 kilometres. Most importantly, two dunes that showed up in both the radar and optical images gave the scientists the clue they needed to get to work. “We started to piece together a model of the way we think the surface behaves,” says Soderblom.

In this model, the area around the Huygens landing site is a huge plain of dirty water ice over which lie blankets of organic (carbon-bearing) deposits that make up the bright highlands and dark dunes. The bright layers are invisible to radar waves, so Cassini SAR images see through to the lower, dirty water ice layer that is rugged in some places and smooth in others.

This digital terrain model (DTM) was constructed thanks to pairs of stereo images obtained by Huygens’s DISR imaging instrument. The images present no vertical exaggeration, and provide perspective views of the surface (45° inclination).

The area shown here is roughly 3 by 5 kilometres wide. The colour-code is such that the difference in elevation between blue and red areas is about 250 metres.

Credits: ESA/NASA/JPL/University of Arizona/SOCET SET-BAE

The deposits form when solar ultraviolet radiation and charged particles react at high altitudes with Titan’s abundant methane to produce carbon- and hydrogen-bearing (hydrocarbon) molecules like ethane and acetylene, and more complex nitrogen-bearing molecules generally called tholins. These products drift down to the surface as aerosols much in the same way smog particles on Earth form and coat surfaces. On Titan however these deposits may accumulate to thicknesses of hundreds of metres deep.

The dunes are composed of sand-sized material that agglomerated, either during its descent or when reworked by geological processes on the surface. The ice and organic landforms are as different from one another as they are spectacular. To the north of Huygens’ landing site are the bright highlands, displaying channels in a very ramified pattern, branching four or five times as they climb into the hills.

Stereoscopic images from the Descent Imager/Spectral Radiometer (DISR) camera on Huygens have now been analysed and show that some of the ridges between the channels rise to 150 - 200 metres in height, with slopes of thirty degrees. “This is extremely rugged terrain,” says Soderblom. The shape suggests that they are drainage channels, cut by liquid methane falling as rain.

This digital terrain model (DTM), constructed thanks to pairs of stereo images obtained by Huygens’s DISR imaging instrument, provides a vertical view of a portion of Huygens’ landing region. A scale for the digital elevation is provided on the left panel: grid spacing is about 50 metres, and elevations are colour-sliced.

Credits: ESA/NASA/JPL/University of Arizona/SOCET SET-BAE

Close - by are stubby canyons with only a few branches. They have probably been formed by ‘spring sapping’, whereby methane flows through the subsurface before emerging as a spring near the base of a hill. The spring erodes the hillside, causing it to collapse and form a cliff face.

The third area is the flat dark plain. This is mostly water ice mixed with tholin grit. “Titan’s river channels, canyons, and flood plains rival the variety seen on Earth,” says Soderblom. The dark plains show markings that suggest the region occasionally experiences flash flooding, but not from the highland drainage channels. Instead large quantities of liquid methane appear to flow from east to west.

Planetary scientists can now begin to piece together the sequence of events that led to the formation of this exotic landscape. “Huygens and Cassini have taken giant steps forward in our understanding of Titan,” says Soderblom.

For more images of the surface of Titan click here.


Notes

This article is based on two papers that will appear in a special issue of the Planetary and Space Science magazine dedicated to Huygens results: ‘Correlation between Cassini VIMS spectra and Radar SRA images: implications for Titan’s surface composition and the character of the Huygens probe landing site’, and ‘Topography and geomorphology of the Huygens landing site on Titan’, by L. Soderblom et al.

Cassini-Huygens is a joint mission between NASA, ESA and the Italian Space Agency (ASI).


For more information

L. Soderblom, U.S. Geological Survey, Flagstaff, Arizona, USA
Email: Lsoderblom @ usgs.gov

Jean-Pierre Lebreton, ESA Huygens Project Scientist
Email : Jean.Pierre.Lebreton @ esa.int

Source: ESA - Cassini-Huygens - News

1 June 2007

Composite view of Titan built thanks to Cassini's images taken on 9 October and 25 October 2006.

Credits: NASA/JPL/University of Arizona


Huygens scored a first in 2005 by measuring the electrical conductivity of Titan’s atmosphere. The results hint at a new way to investigate the subsurface layers of Titan and could provide insight into whether or not Titan has a subsurface ocean.

The Permittivity, Waves and Altimetry (PWA) sensor on the Huygens Atmosphere Structure Instrument (HASI) detected an extremely low frequency (ELF) radio wave during the descent. It was oscillating very slowly for a radio wave, just 36 times a second, and increased slightly in frequency as the probe reached lower altitudes.

If the PWA team confirms that the signal is a natural phenomenon and not an artefact of the way the instrument worked, they will have discovered a powerful new way to probe not just the atmosphere of Titan but its subsurface as well.

The only other world on which ELF waves were detected before was Earth. They are reflected by both the surface of the Earth and its ionosphere, the rarefied region of the atmosphere where most particles are electrically charged. This turns the atmosphere into a giant ‘sound box’ where certain frequencies of ELF waves resonate and are reinforced, whilst other die away.

On Titan, however, the surface is a poor reflector because of its low conductivity and so these waves penetrate the interior. “The wave could have been reflected by the liquid-ice boundary of a subsurface ocean of water and ammonia predicted by theoretical models,” says Fernando Simões, CETP/IPSL-CNRS, France, and a member of the PWA team.

The Permittivity, Waves and Altimetry (PWA) sensor on the Huygens Atmosphere Structure Instrument (HASI) detected an extremely low frequency (ELF) radio wave during the descent. It was oscillating very slowly for a radio wave, just 36 times a second, and increased slightly in frequency as the probe reached lower altitudes.

This sketch illustrates how the radio wave, (if the PWA team confirms that the signal is a natural phenomenon and not an artefact of the way the instrument worked) could provide a powerful new way to probe not just the atmosphere of Titan but its subsurface as well. In fact, the wave could have been reflected by a liquid-ice boundary of a subsurface ocean of water and ammonia predicted by theoretical models.

Credits: ESA/Obs. De Paris Meudon/CETP-IPSLa

If Simões is right, successful modelling of how ELF waves resonate on Titan could lend support to the ocean’s existence and tell scientists about the depth at which it sits. Understanding the resonance however, is difficult.

Above about 100 kilometres altitude on Earth, the ionosphere provides the upper reflecting layer of the resonating cavity. At Titan, PWA revealed that things are more complicated. Apart from the ionosphere, at a much higher altitude of about 1200 kilometres, Huygens found a layer of ionized particles consisting of electrons, at 63 kilometres. “This does not match any previous prediction for Titan,” says Simões. To some extent, it splits Titan’s atmosphere into two resonating chambers.

With so much at stake, the PWA team are checking to make sure the detection is real and not an artefact generated by the spacecraft. They have already ruled out electrical interference from the instrument itself.

Two small arms, one on either side of Huygens, create an antenna and the team’s next goal is to investigate whether the arms could have oscillated during the descent. Simões and colleagues are building a special chamber to hold a replica of the instrument at the low temperature of Titan’s atmosphere, between 100-200 degrees Kelvin (about -173 to -73 °C), in order to check whether the antenna resonates at 36 hertz. If it does, it probably means that the signal is an artefact. If it does not, confidence in the signal’s reality will increase and the investigation of the atmosphere and subsurface can begin.

This graph plots the density of electrons in Titan’s atmosphere versus altitude, as obtained from the HASI instrument on board Huygens. The density of electrons is related to the electrical conductivity in the atmosphere.

Credits: ESA/Obs. De Paris Meudon/CETP-IPSL

But perhaps the biggest mystery is what generated the ELF wave in the first place. On Earth, they are initiated by lightning strikes that make electrons in the atmosphere oscillate, releasing the ELF waves.

The PWA was designed to search for ELF waves on Titan while a microphone on Huygens kept an ear out for thunder – a sure sign of lightning. Cassini has also been watching for lightning using its cameras.

However, Huygens suggests that there is no lightning, or very little. “If there is lightning on Titan, it is significantly less than the amount of lightning that Earth experiences,” says Simões. So what generated Titan’s ELF? No one is quite sure yet. “It might be generated by an interaction with Saturn’s magnetosphere or related to Titan’s intrinsic fields,” suggests Simões. “Titan is proving to be an intriguing environment.”

One thing is certain: there is plenty to investigate. “The measurement of atmospheric electricity is something really new and exciting,” says Jean-Pierre Lebreton, ESA Huygens Project Scientist. “We could send similar instruments to study atmospheric electricity on other celestial bodies, in particular Venus, Mars, and the giant planets,” adds Simões.

The PWA team expect to release more definitive results when their investigation is complete.


Notes

This article is based on two papers that will appear in a special issue of the Planetary and Space Science magazine dedicated to Huygens results: ‘Electron conductivity and density profiles derived from the Mutual Impendence Probe measurements performed during the descent of Huygens through the atmosphere of Titan’, by M. Hamelin et al., and ‘A new numerical model for the simulation of ELF wave propagation and the computation of eigenmodes in the atmosphere of Titan: did Huygens observe any Schumann Resonance?’, by F. Simões et al.

Cassini-Huygens is a joint mission between NASA, ESA and the Italian Space Agency (ASI).


For more information

Fernando Simões, CETP/IPSL-CNRS, France
Email: Fernando.Simoes @ cetp.ipsl.fr

Michel Hamelin, CETP/IPSL-CNRS, France
Email: Michel.Hamelin @ cetp.ipsl.fr

Jean-Pierre Lebreton, ESA Huygens Project Scientist
Email: Jean.Pierre.Lebreton @ esa.int

Source: ESA - Cassini-Huygens - News

1 June 2007

This natural colour image shows Titan's upper atmosphere - an active place where methane molecules are being broken apart by solar ultraviolet light and the byproducts combine to form compounds like ethane and acetylene.

Lower down in the atmosphere, the haze turns into a globe-enshrouding smog of complex organic molecules. This thick, orange-coloured haze absorbs visible sunlight, allowing only perhaps 10 percent of the light to reach the surface.

This image was taken with the NASA/ESA/ASI Cassini spacecraft wide-angle camera using red, green and blue spectral filters, which were combined to create this natural colour view.

The images were obtained at a distance of approximately 9500 kilometres from Titan on 31 March 2005. The image scale is approximately 400 metres per pixel.

Credits: NASA/JPL/Space Science Institute

Planetary scientists are a step closer to understanding the composition of the dust in Titan’s atmosphere. A decade-long programme of laboratory studies, aiming to reproduce Titan’s unique dust, or ‘aerosol’ population in specially constructed reactors, has proved invaluable.

Aerosols are small, solid particles that float in the air. On Earth, they are often the result of pollutants in the atmosphere. On Titan, they occur naturally and are abundant in the atmosphere, masking its surface.

To analyse these particles, Huygens heated the samples to 600 °C, in order to vaporize them into volatile fragments. This technique, known as pyrolysis, was performed by the Aerosol Collector and Pyrolyzer (ACP) experiment. The resultant gases were then passed on to the Gas Chromatograph Mass Spectrometer (GCMS) for analysis.

The GCMS results effectively give scientists a list of chemical components from which they can derive the chemical composition of these particles. Scientists then have to work out what their precise chemical makeup is and determine how they formed. In anticipation ten years ago, a team of French scientists started making their own laboratory analogues, called ‘tholins’, for comparison.

Tholin formation in Titan's upper atmosphere.

Credits: Southwest Research Institute

Tholins are complex nitrogen-rich substances that form in the laboratory when ultraviolet radiation or electrons react with simpler molecules such as methane and ethane in a surrounding atmosphere of nitrogen. On Titan, the methane and nitrogen-rich atmosphere makes their formation easy and they drift to the surface where they continue to react with other atoms and molecules.

Faced with creating such alien molecules, the French team designed a special reaction chamber to simulate Titan’s atmosphere and produce the tholins for study. “We can generate over 200 chemical species,” says Patrice Coll, a team member at Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), Paris, “We do not yet know the detailed pathways that build the chemicals, but we believe that are very similar to those on Titan.”

The aerosols govern what you can see on Titan. They create Titan’s hazy conditions, revealed by Huygens, and give the moon its dull orange glow. If you could stand on the surface of Titan and magically tune your eyes to infrared light, the haze and the clouds would seem to disappear and Saturn would loom large in the night sky. This is because the aerosols are largely invisible at infrared wavelengths. Change your eyes to ultraviolet, however, and you would be plunged into darkness because, at these wavelengths, the tholins behaves like a thick fog that absorbs all ultraviolet radiation falling on it.

The team’s work has already solved one mystery in the data from Huygens by showing that the aerosols must contain ammonia-like structures, even if there was little or no ammonia in the atmosphere from which the particle was built. The team reached this conclusion by analysing the products of the pyrolysis and the ratio of carbon isotopes in their laboratory tholins.

Carbon, in common with many elements, can exist in a number of different isotopes. Isotopes contain different numbers of electrically neutral particles in the atomic nucleus and thus have different weights. An atom’s weight influences how easily it reacts with other atoms. Usually light isotopes react faster and build up into molecules faster than their heavier cousins. Mai-Julie Nguyen, a team member at LISA, analyzed the carbon isotopic ratio in the laboratory tholins and, surprisingly, did not find them to be enriched in the lighter isotope of carbon, in spite of their chemical complexity.

The team then used these new results to interpret the ACP - GCMS data from Huygens. They discovered that the material collected by ACP in Titan’s atmosphere releases ammonia when heated to 600 °C. This gives essential information on the elemental and molecular composition of Titan’s aerosols.

The task of analysing the data from GCMS continues. “This latest paper shows that to correctly interpret these results, we must have clear information about the complexity of the aerosols,” says Francois Raulin, Huygens Interdisciplinary Scientist, at Laboratoire de Physique et Chimie de l'Environnement, Paris.


Notes

This article is based on two papers that will appear in a special issue of the Planetary and Space Science magazine dedicated to Huygens results: ‘Carbon isotopic enrichment in Titan’s tholins? Implications for Titan’s aerosols’, by M. Nguyen et al., and ‘A technique to determine the mean molecular mass of a planetary atmosphere using pressure and temperature measurements made by an entry probe: demonstrating using Huygens data’, by P. Withers.

Cassini-Huygens is a joint mission between NASA, ESA and the Italian Space Agency (ASI).


For more information

Mai-Julie Nguyen, LISA, Paris, France
Email: Nguyen @ lisa-paris12.fr

Paul Withers, Center for Space Physics, Boston Univ. (USA) and The Open University (UK)
Email: Withers @ bu.edu

Jean-Pierre Lebreton, ESA Huygens Project Scientist
Email: Jean.Pierre.Lebreton @ esa.int

Source: ESA - Cassini-Huygens - News

1 June 2007

Artist's impression of the descent and landing sequence followed by ESA''s Huygens probe to Titan.

Credits: NASA

Scientists now know exactly how Huygens made its way to the surface of Titan. The trajectory reconstruction is the culmination of two years of effort and is particularly valuable for a correct interpretation of the observations from all six scientific investigations on board.

It is the culmination of eight years of preparatory work and two years of data analysis by the Huygens Descent Trajectory Working Group.

In any space mission, it is the science data that attracts the most attention. Yet without a precise reconstruction of the path taken by Huygens to reach the surface of Titan, scientists would struggle to put this data into context.

Huygens had an internal clock that time-stamped every measurement that the probe took. “It is crucial to be able to correlate any data measurement to the altitude and speed the spacecraft had at the time of measurement. This is the ultimate goal of the trajectory reconstruction effort,” says Bobby Kazeminejad, co-chair of the Huygens Descent Trajectory Working Group, now working at the German Space Operations Centre (DLR).

The entry point of the Huygens probe in Titan’s atmosphere, and its landing spot on Titan, are respectively indicated by a triangle and a cross on this surface map of Titan. This was assembled from images taken by the Imaging Science Susbsystem (ISS) instrument on board Cassini using a near-infrared filter.

The map reveals complex patterns of bright and dark material on the surface.

Credits: NASA/JPL

Reconstruction of the trajectory was split into three phases. The first phase consisted of the supersonic entry of the probe from an altitude of about 1250 kilometres above Titan’s upper atmosphere down to an altitude of about 100 kilometres. During this time, the heat shield slowed the probe from 22 times down to 1.5 times the speed of sound.

The second phase was the descent phase under the parachute, which overlapped the first phase by starting at an altitude of 145 kilometres and lasted until Huygens landed on Titan’s surface. As soon as the parachute opened, the influence of the wind could clearly be seen. The team split the probe’s movement into two components: vertical and horizontal. The vertical movement was dominated by Titan's gravity, pulling the probe downwards against the resistance of the parachute system. The horizontal movement was determined by the wind blowing it sideways.

This image is a Mercator projection of the surface mosaic composed by the images that Huygens’s Descent Imager and Spectral Radiometer (DISR) took during the descent onto Titan.

The colour coding is such that the left and the right sides of the colour bar correspond to bright and dark areas of the surface, respectively.

Credits: ESA/NASA/JPL/University of Arizona

The team combined temperature and pressure measurements from the Huygens Atmosphere Structure Instrument (HASI) with other measurements from the Surface Science Package (SSP), the Gas Chromatograph and Mass Spectrometer (GCMS), Descent Imager/Spectral Radiometer (DISR) and the Doppler Wind Experiment (DWE) to arrive at their trajectory.

The final phase was the merging of the two reconstructions, using the 145 – 100 - kilometre overlap.

The full results of this effort by Kazeminejad and his colleagues are reported in the special issue of Planetary and Space Science, devoted to the Huygens mission. In the same issue David Atkinson, chair of the Huygens Descent Trajectory Working Group, University of Idaho, explains the organization and structure of the team.

This sketch shows the trajectory that Huygens followed during its descent onto Titan, starting from 40 kilometres altitude. The numbers on the trajectory line indicate the altitude expressed in kilometres, while the dots indicate the position of Huygens every full kilometre of altitude.

Credits: ESA/NASA/JPL/University of Arizona

In addition Erich Karkoschka, University of Arizona, and colleagues report that DISR shows the probe drifted two degrees north of east, while dropping from 145 to 50 kilometres. Between altitudes of 30 and 20 kilometres, it turned five degrees south before resuming its eastward motion. At 6.5 kilometres altitude, it reversed to a west-northwest direction before turning back to a southeast drift at 0.7 kilometres.

Apart from making Huygens drift, the wind also caused the probe to tilt. By analysing the signal strength of the radio link between Huygens and Cassini, a team led by Yvonne Dzierma, Universität Bonn, estimate the probe’s spin, tilt and coning motion during the descent.

Ralph Lorenz, Johns Hopkins University Applied Physics Lab, Maryland, and his colleagues show that the SSP detected similar motions, and revealed a turbulent atmospheric layer between 20 and 30 kilometres. By comparing the motions in this layer with those recorded on terrestrial balloons, Lorenz and his colleagues suggest that the turbulence may have been associated with clouds.

This sketch shows the trajectory that Huygens followed during its descent onto Titan, starting from 2 kilometres altitude. The dots indicate the position of Huygens every 100 metres of altitude.

Credits: ESA/NASA/JPL/University of Arizona

Another report by Lorenz indicates that the density and temperature structure of the atmosphere can be corroborated using data from the engineering sensors on Huygens.

Finally Paul Withers, Boston University, explains that it is possible to determine the mean molecular mass of an atmosphere using pressure and temperature measurements. Traditionally, the mean molecular mass of an atmosphere is determined using a mass spectrometer, such as GCMS. Withers’ new technique will provide a powerful crosscheck on this and future missions.

The success of this effort is particularly significant because the combination of Titan’s dense and cold atmosphere, together with the operational challenges posed by the satellite’s enormous distance from Earth, makes the Huygens trajectory reconstruction unique. “We realised that we could not always apply the standard techniques on Titan; we had to bring in new methods and ideas and start from scratch,” says Kazeminejad.

The final test was whether the defined reconstruction methodology and its implementation could actually provide an accurate landing site location. This was checked against other estimates, such as those from DISR images and the radar measurements from the Cassini orbiter.

All methods showed a remarkably strong agreement as to where Huygens landed. This increases the project’s confidence in that they know exactly how their probe behaved. “Everything converges to the same location,” says Kazeminejad, “All the years of work have paid off.”


Notes

This article is based on five papers to appear in a special issue of the Planetary and Space Science magazine dedicated to Huygens results:

‘DISR imaging and the geometry of the descent of the Huygens probe within Titan’s atmopshere’, by E. Karkoschka et al.,
‘Huygens probe descent dynamics inferred fron Channel B signal level measurements’, by Y. Dzierma, M. Bird et al.,
’Descent motions of the Huygens probe as measured by the Surface Science Package (SSP): turbulent evidence for a cloud layer’, by R. Lorenz et al.,
’Huygens’entry and descent through Titan’s atmosphere – methodology and results of the rajectory reconstruction’, by B. Kazeminejad et al., and
‘The Huygens probe descent trajectory working group: organizational framework, methods and goals’, by D. Atkinson et al.

Cassini-Huygens is a joint mission between NASA, ESA and the Italian Space Agency (ASI).


For more information

Erich Karkoschka, Lunar and Planetary Lab, Univ.Arizona
Email: Erich @ pirl.lpl.Arizona.EDU

Yvonne Dzierma, Geophysikalisches Institut, Univ, Kiel
Email: Ydzierma @ geophysik.uni-kiel.de

Ralph D. Lorenz, John Hopkins Univ. Applied Physics Lab., MD, USA
Email: Ralph.Lorenz @ jhuapl.edu

Bobby Kazeminejad, DLR
Email: Bobby.Kazeminejad @ dlr.de

David Atkinson, Dept. of electrical engineering, Univ.Idaho, USA
Email: Atkinson @ ece.uidaho.edu

Jean-Pierre Lebreton, ESA Huygens Project Scientist
Email: Jean.Pierre.Lebreton @ esa.int

Source: ESA - Cassini-Huygens - News

1 June 2007

Artist's impression of winds on Titan and the Huygens probe.

Credits: Craig Attebery

A simulation of the winds encountered by Huygens has lead planetary scientists to believe that it’s entire atmosphere is circulating around on a conveyor belt. This huge system of moving gas transports warm air from the southern hemisphere to Titan’s north pole and back again.

As on any body with an atmosphere, the direction and speed of the wind encountered at a single point can be related to the general atmospheric circulation. So by reproducing the winds encountered by Huygens during its parachute descent to the surface, planetary scientists have been able to improve their ideas about Titan.

Scenario of the Huygens descent onto Titan on 14 January 2005.

Credits: ESA

At first, all they had to go on with was the way in which Earth’s atmosphere behaved. “Some of the early computer models were actually based on Earth’s circulation,” says Jean-Pierre Lebreton, ESA Huygens Project Scientist. To this they added temperature measurements of Titan’s atmosphere taken by NASA’s Voyager spacecraft and the bulk properties of Titan such as the mass of the world, its rate of rotation, the amount of heating from the Sun and the tides experienced by the gravitational pull of Saturn.

Now, they have the wind profile for the entire descent through the atmosphere to add into the mix – and it is making a world of a difference. “Our knowledge of the low-level atmospheric circulation was virtually absent prior to the Huygens mission,” says Tetsuya Tokano, Institut für Geophysik und Meteorologie, University of Köln, Germany, who has been spearheading the new effort at modelling the atmospheric circulation on Titan.

The Huygens probe descending onto Titan on 14 January 2005 with the first of its three parachutes open. During the descent, the probe encountered winds of different speed.

Credits: Jon Williams/NASA/JPL

Huygens encountered its maximum wind speed about ten minutes after beginning its descent. The speed was roughly 120 metres per second (or 432 kilometres per hour) and was measured at an altitude of about 120 kilometres. As the probe dropped below 60 kilometres, the wind speed dropped too. During the final seven kilometres of the descent, Huygens encountered wind speeds of just a few metres per second, allowing it to drop in an almost straight line. At the surface of Titan, there was nothing but a gentle breeze of just 0.3 metres per second.

These panels are the result of a simulation run with a Global Circulation Model and based on data gathered by Huygens. The panels provide an instantaneous global map of temperature (first three rows) and surface pressure (last row) for the time of the probe’s descent onto Titan.

The temperature maps were simulated for different altitudes: 4.5 kilometres, 300 metres, and ground, respectively. The pressure is simulated for the ground level. The left column shows the results taking into account Saturn’s tidal force, the right column the results without Saturn’s tide

Credits: T. Tokano/University of Köln

During its descent, Huygens found that the winds were flowing in the direction of Titan's rotation, from west to east. The winds reversed direction twice. The first reversal was at six kilometres and the second occurred just 700 metres above the ground. These points have turned out to be vital in understanding the general circulation of Titan’s atmosphere.

Tokano’s model suggests the upper reversal is caused by temperature differences between the north and south. The lower reversal happens at the boundary between the upper and lower portion of a huge circulating pocket of air, known as a Hadley cell. This extraordinarily large ‘cell’ of rotating atmosphere circulates from the south pole to the north pole and back again and is the principal way in which Titan’s atmosphere distributes its warmth.

These panels are the result of a simulation run with a Global Circulation Model and based on data gathered by Huygens. They show a vertical cross-section of temperatures in the meridional lower atmosphere (at different altitudes) of Titan, during day time. ‘Ls’ (on the image) is the solar longitude describing the season. The temperatures are expressed in Kelvin (0 K= - 273.15 °C)

Credits: T. Tokano/University of Köln

On Titan, the southern hemisphere is currently facing the Sun, making it southern summer on the moon. Warm southern ‘air’ rises and flows towards the colder northern hemisphere, forcing colder air from the north down towards the south. This cooler air is less buoyant and hence flows at lower altitudes.

“At the time of the landing of Huygens, the model suggests that Titan must have been warmer at 10 degrees south than it was at the equator,” says Tokano. Southern summer on Titan will last until 2010, when Saturn’s orbit, which governs the moon’s motion, will tilt the northern hemisphere towards the Sun. Such a large Hadley cell is only possible on a slowly rotating world, such as Titan where one day equals 16 Earth days.

These panels are the result of a simulation run with a Global Circulation Model and based on data gathered by Huygens. They show a vertical cross-section of zonal wind speed in the meridional lower atmosphere (at different altitudes) of Titan, during day time. ‘Ls’ (on the image) is the solar longitude describing the season.

Credits: T. Tokano/University of Köln

So, even though Titan may superficially look Earth-like, by feeding the details of the winds encountered by Huygens into a computer model of the moon’s atmospheric circulation, planetary scientists have shown that first impressions can sometimes be deceptive. The wind systems on Titan are unlike those on the Earth, even though they are governed by the same physical principles.

This is good news, for it provides a whole new climatological system for planetary scientists to study.

Notes

This article is based on two papers to appear in a special issue of the Planetary and Space Science magazine dedicated to Huygens results: ’Near-surface winds at the Huygens site on Titan: interpretation by means of a general circulation model’, by T. Tokano, and ‘Titan atmosphere profiles from Huygens engineering (Temperature and acceleration) sensors’, by R. D. Lorenz.

Cassini-Huygens is a joint mission between NASA, ESA and the Italian Space Agency (ASI).


For more information

Tetsuya Tokano, Institut fuer Geophysik und Metorolgie, Univ. of Köln, Germany
Email: Tokano @ geo.uni-koeln.de

Ralph D. Lorenz, John Hopkins Univ. Applied Physics Lab., MD, USA
Email: Ralph.Lorenz @ jhuapl.edu

Jean-Pierre Lebreton, ESA Huygens Project Scientist
Email: Jean.Pierre.Lebreton @ esa.int

Source: ESA - Cassini-Huygens - News

Bright to Dark
June 8, 2007

This Cassini spacecraft view shows the interesting north-south asymmetry in Titan's atmosphere, which is thought to be a seasonal effect.

North on Titan (5,150 kilometers, or 3,200 miles across) is up and rotated 30 degrees to the right.

The image was taken using a spectral filter sensitive to wavelengths of infrared light centered at 889 nanometers. The view was acquired with the Cassini spacecraft narrow-angle camera on May 4, 2007 at a distance of approximately 3 million kilometers (1.9 million miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 54 degrees. Image scale is 18 kilometers (11 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Titan's Cocoon
June 18, 2007

Sunlight scatters through Titan's atmosphere, illuminating high hazes and bathing the entire moon in a soft glow.

This high phase angle view of Titan was acquired from 21 degrees below the smoggy moon's equator. The thin, detached haze layer that extends all the way around Titan is faintly visible.

North on Titan (5,150 kilometers, or 3,200 miles across) is up.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on May 12, 2007 at a distance of approximately 305,000 kilometers (190,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 146 degrees. Image scale is 18 kilometers (11 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Weather Without Water
June 20, 2007

Bright mid-latitude clouds near the bottom of this view hint at the ongoing cycling of methane on Titan. These cloud streaks are near the same latitude as similar clouds observed above different longitudes on Titan.

The view is centered on Titan's trailing hemisphere, over the 1,700 kilometer (1,050 mile) wide bright region known as Adiri.

North on Titan (5,150 kilometers, or 3,200 miles across) is up and rotated 15 degrees to the right.

This view was created by combining multiple images taken using a combination of spectral filters sensitive to wavelengths of infrared light centered at 939 and 742 nanometers

The images were taken with the Cassini spacecraft wide-angle camera on May 13, 2007 at a distance of approximately 104,000 kilometers (65,000 miles) from Titan. Image scale is 12 kilometers (8 miles) per pixel. Due to scattering of light by Titan's hazy atmosphere, the sizes of surface features that can be resolved are a few times larger than the actual pixel scale.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Strange New World
June 22, 2007

Peering through Titan's thick haze, the Cassini spacecraft glimpses boundaries between bright and dark terrain on the moon's trailing hemisphere. The bright terrain at bottom is in northwestern Adiri.

North on Titan (5,150 kilometers, or 3,200 miles across) is up and rotated about 15 degrees to the right.

This view was created by combining multiple images taken using a combination of spectral filters sensitive to wavelengths of infrared light centered at 938 and 619 nanometers. Some processing artifacts remain in the finished image, including the two small, dark circles below and right of center.

The images were taken with the Cassini spacecraft narrow-angle camera on May 13, 2007 at a distance of approximately 237,000 kilometers (147,000 miles) from Titan. Image scale is 3 kilometers (2 miles) per pixel. Due to scattering of light by Titan's hazy atmosphere, the sizes of surface features that can be resolved are a few times larger than the actual pixel scale.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

In Shangri-la
June 27, 2007

This view of Titan's surface highlights northwestern Shangri-la -- a large, equatorial dark region revealed by radar observations to be covered in longitudinal dune fields. The bright, circular feature right of center is a potential impact crater -- few of which have been spotted on Titan thus far.

North on Titan (5,150 kilometers, or 3,200 miles across) is up and rotated about 15 degrees to the right. This view was created by combining multiple images taken using a combination of spectral filters sensitive to wavelengths of infrared light centered at 938 and 619 nanometers.

The images were taken with the Cassini spacecraft narrow-angle camera on May 13, 2007 at a distance of approximately 125,000 kilometers (77,000 miles) from Titan. Image scale is 1 kilometer (0.6 miles) per pixel. Due to scattering of light by Titan's hazy atmosphere, the sizes of surface features that can be resolved are a few times larger than the actual pixel scale.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Titan (T28) Viewed by Cassini's Radar  April 10, 200
July 27, 2007

Cassini's radar instrument obtained its second in a series of four north polar swaths of Titan on April 10, 2007. This image exposes more of the transition between the mid-latitudes and the polar area, and extends coverage of the lakes region previously described in Titan (T25) Viewed by Cassini's Radar - Feb. 22, 2007.

This swath begins at 20 degrees south, 37 degrees west, continuing approximately north-northeast. Although it appears to be straight in this image, its path on Titan curves gently toward the east until it reaches 80 degrees north at 300 degrees west, then it turns south and ends at 51 degrees north, 213 degrees west. The swath width varies from about 200 kilometers (120 miles) at its center to about 500 kilometers (310 miles) at the ends, and is more than 6,700 kilometers (4,100 miles) long.

Beginning at the left end of the image as shown, we see the dark sinuous features previously interpreted to be dunes, interspersed with bright features that appear to be higher. In some cases the dunes seem to bend around the bright features, and in others they may be climbing up onto them; both behaviors are commonly seen in dune fields on Earth. About one-third of the way through the swath, the dunes become rare and then disappear, to be replaced by more linear features. Some of these have rounded and brighter ends, similar to lava flows on Earth (in synthetic aperture radar images, rougher features appear as bright). Just past the midway point, we find relatively flat and featureless terrain with some structures that also resemble flow fronts, followed by a complex area of semi-circular to irregular depressions that may have formed by collapse. These give way to the lakes at the northernmost portion. Here T28 overlaps with the T25 synthetic aperture radar swath (see Titan (T25) Viewed by Cassini's Radar - Feb. 22, 2007), offering stereo coverage that will be used to determine feature heights.

The lakes, which are thought to be filled with a combination of methane and ethane, have complex shorelines that often include channels. Some of these channels have well-developed tributary systems and drain many thousands of square kilometers of the surrounding terrain. As shown in the mosaic (see Exploring the Wetlands of Titan), these lakes are likely connected, and may form part of a larger sea. Brighter areas within the lakes may represent the lake bottom ¿ at the radar's 2-centimeter wavelength, it is possible that the liquid is transparent for many tens of meters (tens of yards) to the radar, allowing a reflection to be returned from the lake bottom.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/home/index.cfm.

Credit: NASA/JPL

Source: NASA/JPL - Cassini

In Shangri-la
June 31, 2007

Within the windswept wastes of Titan's equatorial dune desert lies the 1,700-km (1,050-mi) wide bright region called Adiri, seen here at center. The intrepid Huygens probe landed off the northeastern edge of Adiri in January 2005.

This view looks toward the anti-Saturn side of Titan (5,150 kilometers, or 3,200 miles across) -- the side that always faces away from Saturn as the moon orbits. North on Titan is up and rotated 26 degrees to the right.

The image was taken using a spectral filter sensitive to wavelengths of infrared light centered at 939 nanometers. The view was acquired with the Cassini spacecraft wide-angle camera on June 14, 2007 at a distance of approximately 157,000 kilometers (98,000 miles) from Titan. Image scale is 9 kilometers (6 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

Titan (T30) Viewed by Cassini's Radar -- May 12, 2007
August 13, 2007

This north polar image of Titan was acquired by Cassini's radar instrument on May 12, 2007.

Stretching from 69 degrees north, 329 degrees west to 33 degrees north, 227 degrees west, this swath gently curves from west-to-east at the left end to north-to-south at the right. It is more than 2,700 kilometers (1,678 miles) long and varies from 200 to 500 kilometers (124 to 310 miles) in width, covering the southern extreme of a large dark area previously imaged by the Imaging Science Subsystem (see Exploring the Wetlands of Titan). The thin white stripe at immediate left is an artifact related to the instrument's multi-beam operation; throughout the swath there are some near-vertical stripes that are also artifacts.

As displayed here, the extreme left end of the image shows the west margin of a dark area interpreted to be a lake of liquid methane and probably ethane, with obvious shore-like features, such as bays, inlets and islands. Radar images show smooth areas as dark, and this lake is among the darkest areas seen so far on Titan. The eastern margin of the lake is similarly complex, and some of the shoreline features seem related to ridges and lower topography on the shore, as if the liquid in the lake has filled lower-lying areas between ridges. Some of these channels drain into the lake, while others go into a slightly brighter, more uniform area that may be connected to the lake just off the lower edge of the image (for more details on this area, see Coasts and Drowned Mountains). Farther to the right, moving southward, a complex region of ridges and channels transitions to more subdued landforms with circular or lobate features, some of which have raised rims. The terrain toward the right of the image is rougher, with topographic depressions that resemble dried lakebeds, lacking the dark material seen in the lakes farther north. Toward the right end of the image, farthest from the north pole, a series of long, low depressions is seen against a relatively dark background.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov/home/index.cfm.

Credit: NASA/JPL

Source: NASA/JPL - Cassini

Ring of Twilight
August 16, 2007

This celestial circle of light is produced by the glow of sunlight scattered through the periphery of Titan's atmosphere as the Sun is occulted by Titan. It is the sum of all the sunsets and sunrises taking place on Titan at once.

The intriguing structure of Titan's north polar "hood" can be seen at upper left. A thin, detached, high-altitude global haze layer encircles the moon.

North on Titan (5,150 kilometers, 3,200 miles across) is up and rotated 23 degrees to the left.

The image was taken in visible blue light with the Cassini spacecraft wide-angle camera on June 29, 2007. The view was obtained at a distance of approximately 210,000 kilometers (131,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 167 degrees. Image scale is 12 kilometers (8 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

28 August 2007

This image is an artist’s impression of the descent and landing sequence followed by ESA's Huygens probe that landed on Titan.

Turbulence plays an important role in Earth’s weather system, and can be more than an inconvenience - hundreds of injuries have occurred on commercial flights due to turbulence.

All bodies, planets and moons, are subject to the same principles of physics. So by working together, researchers looking at Earth and those looking at our planetary neighbours can test their models of common processes on both bodies and gain new insights into both.

Investigation of turbulence on Earth has helped identify a turbulent cloud layer in Titan’s atmosphere from Huygens data.

Credits: NASA

Ever spilled your drink on an airline due to turbulence? Researchers on both sides of the Atlantic are finding new ways to understand the phenomenon - both on Earth and on Titan.

Turbulence plays an important role in Earth’s weather system, and can be more than an inconvenience - hundreds of injuries have occurred on commercial flights due to turbulence. It is studied both in Earth's atmosphere and in that of Saturn's moon, Titan, aided by data from ESA’s Huygens probe. The study of one is helping the other.

Giles Harrison, atmospheric physicist at the University of Reading in the UK, devised an inexpensive way to measure the effects of turbulence using weather balloons. The instrument package contains a magnetic field sensor which measures fluctuations in Earth’s magnetic field due to turbulence. As Earth's magnetic field is very stable, the measurements of magnetic changes taken with the weather balloon showed the effects of turbulence on the sensor, since the balloon itself was moving very violently.



All bodies, planets and moons, are subject to the same principles of physics. So by working together, researchers looking at Earth and those looking at our planetary neighbours can really test their models of the processes taking place and gain new insights into both.

Planetary scientist Ralph Lorenz, at the Johns Hopkins University Applied Physics Laboratory in the USA, found Harrison's results key to making sense of data from Huygens, which descended by parachute through Titan's atmosphere in January 2005.

The Surface Science Package (SSP) on board Huygens included a set of tilt sensors which measured motions of the probe during its descent. These tilt sensors act much like a drink in a glass, using a small slug of liquid to measure the tilt angle.

As the probe plummeted under the parachute through Titan’s atmosphere, there was a lot of buffeting, even though the air itself was fairly still. Knowing the signature of cloud-induced turbulence in Harrison's balloon data from Earth inspired Lorenz to look for a similar effect in the Huygens data using the tilt sensor.

“Huygens’ tilt history was just this long, squiggly, complex mess, but seeing the fingerprint of cloud turbulence in Harrison's work showed me what to look for,” said Lorenz.



Armed with that information, Lorenz found that a 20-minute period of Huygens' 2.5-hour descent, around an altitude of 20 km, was affected by this kind of in-cloud turbulence. Having experimented with instrumentation on small models, even frisbees, to understand the dynamics of aerospace vehicles like the probe, Lorenz was familiar with the sensors used by Harrison.

Lorenz’s analysis helped identify a turbulent cloud layer in Titan’s atmosphere - a significant result for the investigation of Titan’s meteorology. In the process, he also found a way to improve Harrison's magnetic sensor arrangement on the weather balloon, simply by changing its orientation.

Mark Leese, Project Manager for the SSP on Huygens at The Open University said “We knew Huygens had a bumpy ride down to Titan’s surface. Now we can separate out twenty minutes of air turbulence – probably due to a cloud layer - from other effects such as cross winds or air buffeting due to the irregular shape of the probe.”


Notes :

Lorenz's analysis ‘Descent motions of the Huygens probe as measured by the Surface Science Package (SSP): turbulent evidence for a cloud layer’, by R. Lorenz, J. Zarnecki, M. Towner, M. Leese, A. Ball, B. Hathi, A. Hagermann and N. Ghafoor, in the online version of the Planetary and Space Science journal. It is expected to appear in print in November this year.

The original work by Harrison and Hogan was published last year in the Journal of Atmospheric and Oceanic Technology, in a paper titled ‘In Situ Atmospheric Turbulence Measurement Using the Terrestrial Magnetic Field— A Compass for a Radiosonde’ by R. Harrison and R. Hogan.

An exchange of ideas between Lorenz and Harrison appears in the August 2007 issue of the Journal of Oceanic and Atmospheric Technology.

Harrison's work is supported by the Paul Instrument Fund of the Royal Society, Lorenz is supported by NASA's Cassini Project. The Science and Technology Facilities Council funds UK participation in the Cassini Huygens mission, in particular, the research at The Open University.

Weather balloons carry packages known as radiosondes, which take (sounding) measurements of air temperature, moisture and wind direction used for weather forecasting. The balloons are filled with helium or hydrogen gas and the measurements are sent back to the surface by radio. When the balloon bursts, usually at 15 to 20 km altitude, the instruments fall to earth by parachute.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.

The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington DC. JPL designed and assembled the Cassini orbiter.

Development of the Huygens probe was managed by ESA’s European Space Technology and Research Centre (ESTEC). ASI managed the development of the high-gain antenna and the other instruments that were part of its contribution.


For more information :

Ralph Lorenz, John Hopkins University Applied Physics Laboratory, USA
Email : Ralph.Lorenz @ jhuapl.edu

Giles Harrison, Department of Metrology, University of Reading, UK
Email : R.G.Harrison @ reading.ac.uk

Jean-Pierre Lebreton, ESA Huygens Project scientist
Email : Jean-Pierre.Lebreton @ esa.int

Source: ESA - News

Titan's Hazes
October 1, 2007

Titan's detached, high-altitude haze layer encircles its smoggy globe in this ultraviolet view, which also features the moon's north polar hood. The northern hemisphere is currently in its Winter season.

Titan is 5,150 kilometers (3,200 miles) across.

The image was taken with the Cassini spacecraft narrow-angle camera on Sept. 2, 2007 using a spectral filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers. The view was obtained at a distance of approximately 1.3 million kilometers (816,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 20 degrees. Image scale is 8 kilometers (5 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Source: NASA/JPL - Cassini

The University of Chicago press release is reproduced below:

By Steve Koppes
News Office


If space travelers ever visit Saturn’s largest moon, they will find a tropical world where temperatures plunge to minus 274 degrees Fahrenheit, methane rains from the sky and dunes of ice or tar cover the planet’s most arid regions. These conditions reflect a cold mirror image of Earth’s tropical and subtropical climates, according to scientists at the University.

“You have all these things that are analogous to Earth. At the same time, it’s foreign and unfamiliar,” said Ray Pierrehumbert, the Louis Block Professor in Geophysical Sciences and the College.

Titan, one of Saturn’s 60 moons, is the only moon in the solar system with a dense atmosphere. Pierrehumbert and Jonathan Mitchell, a recent Ph.D. graduate in Astronomy & Astrophysics, have been comparing observations of Titan collected by the Cassini space probe and the Hubble Space Telescope with their own computer simulations of the moon’s atmosphere.


This image depicts Saturn’s moon Titan as seen by the
visual and infrared mapping spectrometer after closest
approach on a July 22, 2006 flyby. The clouds, shown
here in light orange and spreading out along the 40-
degree-south latitude line, are of the type seen before
and reported in the journal Science.
(Image courtesy of NASA/JPL/University of Arizona)

Their study of the dynamics behind Titan’s methane clouds have appeared in the Proceedings of the National Academy of Sciences. Their continuing research on Titan’s climate focuses on the moon’s deserts.

“One of the things that attracts me about Titan is that it has a lot of the same circulation features as Earth, but done with completely different substances that work at different temperatures,” Pierrehumbert said. On Earth, for example, water forms liquid and is relatively active as a vapor in the atmosphere. But on Titan, water is a rock. “It’s not more volatile on Titan than sand is on Earth.”

Methane, natural gas, assumes an Earth-like role of water on Titan. It exists in enough abundance to condense into rain and form puddles on the surface within the range of temperatures that occur on Titan.


The poster at left shows a composite view
from the descent imager/spectral radiometer
taken while the European Space Agency’s
Huygens probe was setting on Titan’s surface,
juxtaposed with a similarly scaled picture
taken on the Moon’s surface. Objects near
the center of the picture are roughly the
size of a man’s foot. Objects at the horizon
are a fraction of a man’s height.
(Image courtesy of ESA/NASA/JPL/
University of Arizona)

“The ironic thing on Titan is that although it’s much colder than Earth, it actually acts like a super-hot Earth rather than a snowball Earth, because at Titan temperatures, methane is more volatile than water vapor is at Earth temperatures,” Pierrehumbert said. Pierrehumbert and Mitchell go so far as to call Titan’s climate “tropical,” even though it sounds odd for a moon that orbits Saturn more than nine times farther from the sun than Earth. Along with the behavior of methane, Titan’s slow rotation rate also contributes to its tropical nature. Earth’s tropical weather systems extend only to plus or minus 30 degrees of latitude from the equator. But on Titan, which rotates only once every 16 days, “the tropical weather system extends to the entire planet,” Pierrehumbert said.

Titan’s tropical nature means that scientists can explain the behavior of its clouds using theories they have relied upon to understand Earth’s tropics, Mitchell noted. Titan’s atmosphere produces an updraft where surface winds converge. This updraft lifts evaporated methane up to cooler temperatures and lower pressures, where much of it condenses and forms clouds.

“This is a well-known feature on Earth called an ITCZ, the inter-tropical convergence zone,” Mitchell said. Earth’s oceans help confine the ITCZ to the lowest latitudes. But in some scenarios for oceanless Titan, the ITCZ in Mitchell’s computer simulations wanders in latitude almost from one pole to the other. Titan’s clouds also should follow the ITCZ.

Titan’s orange atmospheric haze complicates efforts to observe the moon’s clouds. “This haze shrouds the entire surface,” Mitchell said. “It pretty much blocks all visible light from reaching us from the surface or from the lower atmosphere.”

Nevertheless, infrared observations via two narrow frequency bands have recently revealed that clouds are currently confined to the moon’s southern hemisphere, which is just now emerging from its summer season.

“There should be a very large seasonality in these cloud features,” Mitchell said. “Cassini and other instruments might be able to tell us about that in the next seven to 10 years or so, as the seasons progress.”

Mitchell and Pierrehumbert’s next paper will describe how oscillations in Titan’s atmospheric circulation dry out the moon’s midsection. Over the course of a year, Mitchell explained, “this oscillation in the atmosphere tends to transport moisture, or evaporated methane, out of the low latitudes and then deposit it at mid- and high-latitude in the form of rainfall. This is interesting, because recent Cassini observations of the surface suggest that the low latitudes are very dry.”

Cassini images show dunes of ice or tar covering these low-latitude regions that correspond to the tropics on Earth. When ultraviolet light from the sun interacts with methane high in Titan’s atmosphere, it creates byproducts such as ethane and hydrogen. These byproducts become linked to chains of hydrocarbon molecules that create Titan’s orange haze. When these molecules coalesce into large particles, they settle out as a tar-like rain.

“Titan is like a big petrochemical plant,” Pierrehumbert said. “Although this is all happening at a much lower temperature than in a petroleum refinery, the basic processes going on there are very closely allied to what people do when they make fuel.”

Source: University of Chicago press release

October 11, 2007
(Source: Jet Propulsion Laboratory)

Newly assembled radar images from the Cassini spacecraft provide the best view of the hydrocarbon lakes and seas on the north pole of Saturn's moon Titan, while a new radar image reveals that Titan's south polar region also has lakes.


Titan's North Polar Region
+ View Movie (QuickTime, 8.0 MB)

The southern region images were beamed back after an Oct. 2 flyby in which a prime goal was the hunt for lakes at the south pole.

A new mosaic image, created by stitching together radar images from seven Titan flybys over the last year and a half, shows a north pole pitted with giant lakes and seas, at least one of them larger than Lake Superior.

Approximately 60 percent of Titan's north polar region above 60 degrees latitude has been mapped by Cassini's radar instrument. About 14 percent of the mapped region is covered by what scientists interpret as liquid hydrocarbon lakes.

"This is our version of mapping Alaska, the northern parts of Canada, Greenland, Scandinavia and Northern Russia," said Rosaly Lopes, Cassini radar scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It's like mapping these regions of Earth for the first time."


Radar Sees Lakes in Titan's Southern Hemisphere

Lakes and seas are very common at the high northern latitudes of Titan, which is in winter now. Scientists say it rains methane and ethane there, filling the lakes and seas. These liquids also carve meandering rivers and channels on the moon's surface. Now Cassini is moving into unknown territory, the south pole of Titan. "We wanted to see if there are more lakes present there and, sure enough, there they are, three little lakes smiling back at us. Titan is indeed the land of lakes and seas," said Lopes. "It will be interesting to see the differences between the north and south polar regions."

It is now summer at Titan's south pole. A season on Titan lasts nearly 7.5 years, one quarter of a Saturn year, which is 29.5 years long. Monitoring seasonal change helps scientists understand the processes at work there.

Scientists are making progress in understanding how the lakes may have formed. On Earth, lakes fill low spots or are created when the local topography intersects a groundwater table. Lopes and her colleagues think that the depressions containing the lakes on Titan may have formed by volcanism or by a type of erosion (called karstic) of the surface, leaving a depression where liquids can accumulate. Karstic lakes are common on Earth. For example in parts of Minnesota and central Florida there are hundreds of such lakes.

"The lakes we are observing on Titan appear to be in varying states of fullness, suggesting their involvement in a complex hydrologic system akin to Earth's water cycle. This makes Titan unique among the extra-terrestrial bodies in our solar system," said Alex Hayes, a graduate student who studies Cassini radar data at the California Institute of Technology in Pasadena.

"The lakes we have seen so far vary in size from the smallest observable, approximately 1 square kilometer (0.4 square miles), to greater than 100,000 square kilometers (40,000 square miles), which is slightly larger than the Great Lakes in the Midwestern U.S.," Hayes said. "Of the roughly 400 observed lakes, 70 percent of their area is taken up by large "seas" greater than 26,000 square kilometers (10,000 square miles)."

Future radar flybys will image closer to the southern pole and are expected to show more lakes.

For images and more information visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.

Contacts:
Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez@jpl.nasa.gov


NEWS RELEASE: 2007-117

Source: NASA/JPL - Cassini - News Release

Titan's North Polar Region
October 11, 2007

+ View Related Movie (8.0 MB, QuickTime)

This Cassini false-color mosaic shows all synthetic-aperture radar images to date of Titan's north polar region. Approximately 60 percent of Titan's north polar region, above 60 degrees north latitude, is now mapped with radar. About 14 percent of the mapped region is covered by what is interpreted as liquid hydrocarbon lakes.

Features appearing darkest to the radar, which are thought to be liquid, are shown in blue and black, and the radar-bright areas likely to be solid surface are tinted brown. The terrain in the top center of this mosaic is imaged at lower resolution than the remainder of the image.

Most of the many lakes and seas seen so far are contained in this image, including the largest known body of liquid on Titan. These seas are most likely filled with liquid ethane, methane and dissolved nitrogen.

Many bays, islands and presumed tributary networks are associated with the seas. The large feature in the upper right center of this image is at least 100,000 square kilometers (40,000 square miles) in area, greater in extent than Lake Superior (82,000 square kilometers or 32,000 square miles), one of Earth's largest lakes. This Titan feature covers a greater fraction of the surface, at least 0.12 percent, than the Black Sea, Earth's largest terrestrial inland sea, at 0.085 percent. Larger seas may exist, as it is probable that some of these bodies are connected, either in areas unmapped by radar or under the surface (See Exploring the Wetlands of Titan).

Of the 400 observed lakes and seas, 70 percent of their area is taken up by large "seas" greater than 26,000 square kilometers (10,000 square miles).

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/home/index.cfm.

Credit: NASA/JPL/USGS

Source: