Visions of the Cosmos

Planetary Science

The Solar System

Titan

Unmasking the mystery of Titan - the smog enshrouded enigma

The story of Titan goes back over three hundred years when it was discovered by a young genius from the Netherlands named Christiaan Huygens 14 April 1629 – 8 July 1695.   At the early age of 26 he discovered Titan on 25 March 1655 when he observed a  tiny point of light that changed its position relative to Saturn approximately every sixteen days before coming back to its original place. He realised that he had discovered a large satellite of the ringed planet.  In doing so he also observed that its time of orbit around Saturn was just under 16 (Earth) days.  Ever since that early discovery Titan has remained a fascinating mystery.

An excellent biography of Huygens, entitled Titan, by C.D.Andriesse translated into English by Sally Miedema was published in 2003 by the University of Utrecht.  The ISBN number is 90 3933 462 5.

 

Portrait by Caspar Netscher in Haags Historisch Museum Dutch stamp Commemorative Stamp.  Huygens was born 14 April 1629 and died on 8 July 1695  Grenada Stamp of 2000. actually Huygens discovered Titan and studied the Rings of Saturn

The Cassini-Huygens Mission to the Saturn System

The Mission is named after two great scientists of the 17th century -  Cassini who was born in Italy as Giovanni Domenico Cassini. He is often known by his French name Jean-Domininique Cassini and Christiaan Huygens who was born in Den Haag in the Netherlands.

After years of hard work and planning, a mission was undertaken to study Saturn and Titan as well as the other moons.  It was the most ambitious international voyage of space discovery ever undertaken with contributions from scientists, engineers and technicians and many other workers from all the countries of the European Space Agency, the Italian Space Agency, from the many departments of the American NASA and from Canada and Poland..  To see this co-operation between so many nations was both heartening and inspiring.

Title Page Proceedings of Cassini-Huygens Conference
held at ESTEC Noordwyk Netherlands 13-17 April 2004
ESA Publications   Courtesy European Space Agency

In April 2004, An International Conference was held in the Netherlands to celebrate both the mission and the 375th anniversary of the birth of Huygens. On Page 224 of the Proceedings Tobias Owen of the University of Hawaii sums up the feelings of the people involved in the project:
‘It was particularly satisfying to participate in an international activity whose goal was to produce a device at the cutting edge of technology that was not designed to kill anyone, but instead to give new knowledge to the world. “These spacecraft are our cathedrals,” Hal Marsursky said, and I think his perspective was exactly right’.
On the Wednesday afternoon the delegates to the conference had the pleasure of a conducted tour round the Leiden Museum where many of the instruments built by Huygens could be seen.  Leiden is the oldest University in the Netherlands and is still at the forefront of  work  in the astronomical sciences.  They also visited one of the houses in which Huygens had lived.

The conference was essentially divided into two sections.  The first part was devoted to the life and work of the great scientist and was held on the 375th anniversary of his birth.  The second part was devoted to the Cassini-Huygens Mission with considerable emphasis on the investigation of Titan.  The proceedings of the international conference have now been published and interested parties should contact

ESA Publications Division, C/O ESTEC, PO Box 299,  2200 AG Noordwyk, The Netherlands. Phone 00 31 71 565 3400

The mission was years in the planning which was started in the early 1980s.  It was not until 1997 that it began its epic journey to Saturn - ' Lord of the Rings' and Titan, its mysterious moon

Illustration Cassini-Huygens on its way to Saturn and Titan On 15 October 1997 the Spaceship left its Launch-pad in Cape Canaverel and thundered into the night on its epic journey which took it past Venus, Earth and Jupiter to the giant planet Saturn, and its smog enshrouded moon Titan
From Earth to the Saturn System 15 October 1997 – 1 July 2004 Diagram acknowledgement NASA/ESA.

Gravity Assists Fly-bys.  The VVEJGA Trajectory Diagram Pparc - CCLRC

 From Earth to the Saturn System 15 October 1997.   Illustrations Acknowledgement NASA/ESA

Diagram of the Trajectory Courtesy NASA/JPL/Caltech.

  

Cassini's  trajectory was designed to get a 5650 kilogram (about 12,450 pounds, or a small school bus!) spacecraft to the Saturn system in about six years and nine months. The Cassini spacecraft was initially aimed toward Venus rather than Saturn. After examining literally thousands of different possible paths, the mission designers came up with an outstanding trajectory, consisting of two Venus flybys, a flyby of Earth and one of Jupiter. Only after these four "gravity assists" was the spacecraft finally able to reach Saturn. It had "stolen" speed from the planets by using their gravitational fields.

 

When the Voyager spacecraft flew by Jupiter, it gained 16 kilometers per second of speed at a cost of slowing down Jupiter by 30 centimetres every trillion years!

 

 

The Cassini mission was launched on 15 October 1997 using the Titan IV/Centaur, with an Upgraded Solid Rocket Motor (SRMU).  The  first Venus fly-by was in April 1998 and the second was in June 1999.

The Earth flyby occurred in August 1999 and set the spacecraft on its journey to the outer planets.  It reached its nearest point to Jupiter in late December 2000

The primary trajectory took advantage of the fact that Jupiter, which is by far the most massive planet in the Solar System (and therefore, the best to use for gravity assists), was in the right spot with respect to Saturn  for it to be used  as the last slingshot. When the Voyager spacecraft flew by Jupiter, it gained 16 kilometers  per second of speed at a cost of slowing down Jupiter by 30 centimetres every trillion years!

The Cassini-Huygens journey covered an enormous distance. Saturn is almost ten times as far from the Sun as is the Earth -  about 1,430,000,000 kilometers (900,000,000 miles). From the spacecraft's point of view, the trip is equivalent to that of an ant that has to crawl around the Earth 60 times! Without gravity assists or a much larger launch rocket, we just couldn't get there at all. A copy of the VVEJGA trajectory timetable is shown below
Date Planet Distance from Surface
27 April 1998 Venus

284 km

24 June 1999 Venus

603 km

18 August 1999 Earth

1173 km

30 December 2000 Jupiter

9 720 000 km

During its Voyage Cassini carried out some valuable observations on Jupiter and its moons.  Details of these observations can be found on the page of this web dealing with the moons of Jupiter.

The spacecraft arrived at the Saturn system on 30 June 2004

The whole operation of inserting the space craft was already pre-programmed since nothing could be done from the Earth . There was an 84 minute difference between the actual event time and the recorded event time on Earth due to the distance between the Earth and Saturn.  In other words Saturn was 84 light minutes away from Earth.

In order to slow the spacecraft significantly enough to be captured by Saturn's gravity, Cassini's main engine was turned to face the direction of travel. The resulting thrust from the engine acted as a braking device, slowing down the spacecraft as it entered Saturn's orbit. The procedure is called the Saturn Orbit Insertion (SOI) burn and it was critical to the success of the mission at Saturn.

Cassini-Huygens' closest approach to Saturn, during the entire four-year tour, occurred during this burn. The spacecraft's distance from Saturn was approximately 0.3 Saturn Radii (20 000 km).

Cassini-Huygens continued to coast above the rings for approximately one hour and 44 minutes before its descent back through the ring plane.  The amazing manoeuvre took the space craft through the division between the two main sets of rings known as 'The Cassini Division' after Cassini who first discovered it.

The spacecraft's close proximity to the planet and its rings provided a unique opportunity for an in-depth study of the planet, by utilizing the appropriate instruments onboard the spacecraft to conduct studies in waves, particles and imaging data.  Illustrations  Courtesy ESA Multimedia.  The first illustration on the left shows the Cassini Division very clearly and the one of the right shows the burn as the spacecraft was above the rings just before plunging through the Cassini Division.

Titan before the Probe – The Smog Enshrouded Enigma
 

In the cold outer reaches of the Solar System, over nine times as far from the Sun as is the Earth, Titan orbits the great gas giant planet Saturn – The Lord of the Rings. It is Saturn’s only really large moon and is a planet in its own right. It is the only satellite in the Solar System that has an appreciable atmosphere. Floating in the atmosphere are orange coloured solids called tholins. They produce a thick smog like environment that conceals the nature of the surface below. Before the landing of the Huygens Probe and the photography taken from the Cassini mother ship it was suggested that seas or even oceans of methane or a mixture of ethane and methane lie concealed beneath the thick tholin clouds. It was indeed a mystery which scientists hoped to solve on the Cassini-Huygens space mission. The investigations are taking the form of close-up photography at a number of wavelengths, the use of radar mapping and the data obtained by the Huygens probe which landed on the on the planet itself. It will take scientists many years to complete the interpretation of the data.

 

Titan from Voyager 1 in November 1980

Titan's surface cannot be seen in any Voyager photos; it is hidden by a dense, photochemical haze whose main layer is about 300 kilometers (200 miles) above Titan's surface. Several distinct, detached haze layers can be seen above the opaque haze layer. The haze layers merge with the main layer over the north pole of Titan, forming what scientists first thought was a dark hood. The hood was found, under the better viewing conditions of Voyager 2, to be a dark ring around the pole. The southern hemisphere is slightly brighter than the northern, possibly the result of seasonal effects. When the Voyagers flew past, the season on Titan was the equivalent of mid-April, early  spring in the northern hemisphere and early autumn in the south.

Xanadu on Titan from Hubble Space Telescope and from Cassini. of Xanadu

 Throughout the years many images of the planet have been taken.  The earlier ones told us almost nothing about the surface of this enigmatic world which was enshrouded by an orange smog apparently due to the presence of tholins in the upper atmosphere.  By 1994 images taken by the Hubble Space Telescope suggested the presence of a large ‘continent’ about the size of Australia which was given the name Xanadu.  The exact significance of this image was however not known although some investigators suggested that it was high ground.   Later images obtained by the cunning use of ‘windows’ at certain wavelengths and by radar have been taken from close fly-bys of the Cassini.  The photograph on the left shows four views of Titan taken from the Hubble Space Telescope in 1994. The large bright area was estimated to be about the size of Australia and was given the name Xanadu. It was though to be due to a high altitude plateau. Credit Hubble Space Telescope NASA/ESA

The image on the left was taken on 24 October 2004 and reveals Titan's bright 'continent-sized' terrain known as 'Xanadu'. It was acquired with the narrow-angle camera on the Cassini-Huygens Imaging Science Subsystem through a spectral filter centred at 938 nanometres, a wavelength region at which Titan's surface can be most easily detected. Credits NASA/JPL/Space Science Institute

Surface materials with different brightness properties (or albedos) rather than topographic shading are highlighted. The image has been calibrated and slightly enhanced for contrast. It will be further processed to reduce atmospheric blurring and to optimize mapping of surface features. The origin and geography of Xanadu remain a mystery at this range. Bright features near the south pole (bottom) are clouds.  

The Construction of the Spacecraft and the Huygens Probe

 

The Cassini Spacecraft was at least as large as a double-decker bus or a small house as the pictures show .  The Huygens Probe was attached to the side of the mothership and an important part of the construction was the fixing of the Heat Shield as the photograph illustrates

When it plunged through the upper atmosphere the main probe was protected from the intense heat of entry by the heat shield  The illustration on the left shows the back cover being fitted to the main probe. .  The Huygens Probe can be seen being attached to the Mothercraft in the picture on the right

 

Pictures by courtesy of ESA micromedia library

 

Sometime before the actual landing a number of artist's impressions were published by the European Space Agency.

 

Huygens is released from the mother craft and Huygens is on its way to Titan.  The picture on the extreme left is an artist's impression by David Ducros of the Huygen's Probe leaving the Cassini mothership.  This actually happened on 24/25 December 2004.

Huygens enters the atmosphere protected by the heat shield

 Credit illustrations by ESA

 

  

The parachute has opened and the Huygens Probe drifts through the clouds towards the surface.  The heat shield has accomplished its task of protecting the probe during entry into the dense atmosphere and drops away.

The probe lands on the surface of Titan. 

These artist's impressions were released by ESA before the Cassini-Huygens spacecraft reached Saturn.

 

 The Unveiling of the Enigma

 On 14 January 2005, the Huygens Probe successfully plunged through the atmosphere of the orange smog-enshrouded world and parachuted down onto a solid surface

The Huygens probe remained dormant until the onboard timer ‘woke it up’ just before the probe reached Titan's upper atmosphere on the 14th of January 2005. Then it began its dramatic plunge through Titan's murky atmosphere, tasting its chemical makeup and composition as it descended to touch down on its surface. The data gathered during this two and a half hour descent was transmitted from the probe to the Cassini orbiter. Afterwards, Cassini pointed its antenna in the direction of the Earth (see diagram below) and relayed the data through NASA's Deep Space Network to the Jet Propulsion Laboratory (JPL) in Pasadena California and on to the European Space Agency's Space Operations Center in Darmstadt, Germany, which served as the control center for the Huygens mission. From this control center, ESA engineers were tracking the probe and waiting in eager anticipation for the landing. Before they got the signals from the mother ship they actually picked up weak signals from the probe itself from the Radio Telescopes to say that it had entered the atmosphere and successfully landed. Then after three long minutes when nothing appeared on the screens they watched as the streams of data came in from the distant Saturn System over one light hour from Earth.
From left to right, Mr. Lebreton, Mr. Southwood and Mr. Bonacina on 15 January 2006, during the press conference for the landing of the Huygens probe on Titan. ESA Micromedia. 
Jean-Pierre Lebreton is Project Scientist for ESA's Huygens probe.

On that historic night the BBC showed a truly impressive live broadcast programme of the scenes of jubilation by the scientists and engineers at the European  Space Centre in Darmstadt as they watched the success of years of work come to fruition.  Professor John Zarnecki who was in charge of the Surface Science Package and the probe and the Director of CESPAR of the  gave a graphic account of the wonderful achievement.  David Southwood, the Director of Science (D/SCI), in charge of the ESA Science Programme, appeared on the screen to express his great joy at the achievement of the scientists, engineers and support staff of the European Space Agency who had by their dedicated effort succeeded in landing a space probe on that very distant little world so far from Earth.

Communications from the  Cassini Spacecraft and from the Huygens Probe to Earth

To communicate with and to receive messages from the Cassini Spacecraft three ground stations are used – one in Goldstone in California, another in Madrid Spain and a third one in Australia. This allows for the constant receipt of data from Cassini
 

Illustrations Credit ESA

 

At 11:25 CET the Robert C. Byrd Green Bank Telescope (GBT) of the National Radio-astronomy Observatory in West Virginia, USA, a part of the global network of radio telescopes involved in tracking the Huygens Titan probe,  detected the probe's 'carrier' (tone) signal.
 
The detection occurred between 11:20 and 11:25 CET, shortly after the probe began its parachute descent through Titan's atmosphere. The extremely feeble signal was first picked up by the Radio Science Receiver supplied by the NASA Jet Propulsion Laboratory. This signal was an important indication that the Huygens probe was 'alive'. However, it did not contain yet any other information ; the latter came a few hours later via the Cassini spacecraft. What the Green Bank radio telescope  detected was only a ‘carrier’ signal. It indicates that the back cover of Huygens must have been ejected, the main parachute must have been deployed and that the probe has begun to transmit, in other words, the probe was ‘alive’. This, however, did still not mean that any data have been acquired, nor that they had been received by Cassini. The carrier signal was sent continuously throughout the descent but did not contain any other scientific data. It is similar to the tone signal heard in a telephone handset once it is picked up

 

 

 

 

 

 

 

Illustration on left -Titan's atmosphere is cold and thick; the pressure at the surface is one and a half times that on Earth. Like Earth's, it consists mostly of nitrogen, but it lacks oxygen and ethane clouds always obscure the surface, which is nearly 200degC below the freezing point of water. [Image Date: 01-01-97] [97.06.001-002] ESA

Picture on right artist's impression of the Huygens descent and landing Credit ESA Artist C. Carreau Enlargement  Click Hyperlink

Titan is a desperately cold, forbidding place with a surface temperature of around –180 degrees Celsius. However scientists believed that it may have one thing found nowhere else in the Solar System besides Earth: lakes and rivers.
"I'm just staggered by the level of detail," said European Space Agency science chief David Southwood, examining images of Titan captured by the agency's Huygens space probe on Friday 14 January 2005.
The exultant scientists gazed at the television screens at mission control in Darmstadt, Germany and watched the images of the pictures taken by the Huygens Probe as it parachuted through Titan's smoggy atmosphere and came to rest on a rock-strewn plain bathed in orange twilight, with a spongy surface topped by a thin crust. "The closest analogues are wet sand or clay," said John Zarnecki, in charge of instruments analysing Titan's surface.
The imaging team presented its first panoramic view of Titan's surface on 15 February, showing a broad expanse of what looked like a coastline with crags and glacier-like deposits.
The "sea" in the panorama may have be a true liquid methane sea but it is in fact a flat plain of mushy hydrocarbon slush.
An early-Friday photo suggested a glacier-like wall of sludge moving toward the "coastline." All of this suggested that Titan's surface is a shifting, oozing combination of gravel, ‘stones’ of ice, hydrocarbon sludge and, possibly, methane lakes or ponds with traces of ethane and other hydrocarbons.
Composite picture derived from images taken during the descent of ESA’s Huygens Probe from an altitude of about 8 kilometres. Acknowledgement ESA/NASA/University of Arizona
Finally the probe came to rest on a stone strewn surface.  The pebbles were of course not made of silicate rock but of water ice.  At the very low temperatures on Titan the rocks are made of solid water ice probably with traces of other substances.   The raw image was returned on 14 January 2005, by ESA's Huygens probe during its successful descent to land on Titan. Sizes have been added to indicate scale of these features. Initially thought to be rocks or ice blocks, they are more pebble-sized. The two rock-like objects just below the middle of the image are about 15 centimetres (left) and 4 centimetres (centre) across respectively, at a distance of about 85 centimetres from the Huygens Probe. The surface is darker than originally expected, consisting of a mixture of water and hydrocarbon ice. There is also evidence of erosion at the base of these objects, indicating possible fluvial activity.

The astonishing details in the pictures and the wealth of information captured by the other scientific instruments carried by the probe as well as the results of radar mapping and other observations made by the Cassini mother-ship will keep the scientists busy for decades.    Credits: ESA/NASA/JPL/University of Arizona

A picture on the left shows the view of Titan from the VIMS instrument on the Cassini orbiter. The Huygens probe landed in the small red circle on the boundary of the bright and dark regions. The size of the circle shows the field of view of the Huygens DISR imager from an altitude of 20 kilometres. 
                                                                                   The picture on the left is an artists impression of the probe on the landing site

Credits: ESA/NASA/JPL/University of Arizona

Observation of Titan from the Cassini Spacecraft

The landing of the probe on Titan is by no means the end of the investigations of this fascinating moon.  The main Cassini spacraft is returning again and again to the vicinity of Titan and taking photographs through the clouds using 'windows' at a variety of wavelengths and also making radar observations.   The amount of information that is being received is so great that it will take years to process and interpret it.

This view of Titan's south polar region reveals an intriguing dark feature, seen here at left of centre, that may be the site of a past or present lake of liquid hydrocarbons. A red cross below centre in the scene marks the pole. The brightest features seen here are methane clouds.

This view is a composite of three NASA/ESA/ASI Cassini spacecraft narrow-angle camera images, taken over several minutes during Cassini's distant fly-by on 6 June 2005. The images were combined to produce a sharper view of Titan's surface. The images were taken using a combination of spectral filters sensitive to wavelengths of polarised infrared light.

The images were acquired from approximately 450,000 kilometres from Titan. Resolution in the scene is approximately 3 kilometres per pixel. The view has been contrast-enhanced to improve the overall visibility of surface features

Courtesy ESA/NASA/ASI  Can be found on the ESA Micromedia library on the ESA web-site

' Titan's Sierras' Credit NASA/JPL/University of Arizona and

'Two new Titan features - water ice and methane springs'. Credits   ESA/NASA/JPL/University of Arizona

The picture on the left is a composite image showing a massive mountain range running just south of Titan’s equator. Near the centre of the image, the mountain range runs from southeast to northwest. It is about 150 kilometres long and 30 kilometres wide and about 1.5 kilometers high. This range, and smaller ranges to the west and east of the main range, probably results from material welling up below as the crust of Titan is pulled apart by tectonic forces.

This image was obtained during a fly-by of Titan designed to obtain the highest resolution infrared views of Titan yet. The fly-by took place on 25 October 2006. Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) resolved surface features as small as 400 meters. This image was constructed from images taken at wavelengths of 1.3 microns shown in blue, 2 microns shown in green, and 5 microns shown in red.

The picture on the right shows a single Huygens DISR image that shows two new features on the surface of Titan. A bright linear feature suggests an area where water ice may have been extruded onto the surface. Also visible are short, stubby dark channels that may have been formed by 'springs' of liquid methane rather than methane 'rain'.

Cryovolcanoes on Titan

Titan is a difficult object to study. The Cassini instruments are specifically designed to penetrate the haze, its radar mapper can see right through it and the Huygens images show the surface clearly. But the orbiter images are still frustratingly vague and the Huygens images are few in number and cover only a tiny area. Analysis of this data will take some time; Titan is a very strange place.

Prior to Cassini's arrival, it seemed likely that the clouds would produce a rain of ethane or methane onto the surface perhaps producing an "ocean" up to 1000 meters deep. However, this seems not to be the case at least at the present time. There is little doubt that some active processes are occurring on Titan; there are few if any craters visible indicating that the surface must be very young.  But it may be that the "lakes" are more slushy than liquid or that the basins are not filled with liquid at all times. Preliminary results from Huygens indicate that while Titan's rivers and lakes appear dry at the moment, rain may have occurred not long ago. There is clear evidence for "precipitation, erosion, mechanical abrasion and other fluvial activity".

This high-resolution infrared image was taken by the NASA-ESA Cassini-Huygens mission during the first Titan fly-by on 26 October 2004, just before closest approach. The spatial resolution of the images, acquired by the VIMS instrument on board the Cassini orbiter gradually approaching Titan's surface, ranges between 2.6 and 1.8 kilometres per pixel. On the centre-right of the image a bright circular structure can be seen, which is interpreted as a volcanic Credit NASA/VIMS

The illustration shows pictures taken over a number of nights in February 2004 from the European Southern Observatory’s Very Large Telescope.  From these photographs the various possible four 'ocean areas' have been observed.  During February 2004 an unprecedented series of images were obtained using the European Southern Observatory’s Very Large Telescope. The results were posted on 25 April 2004 and the images shown above 'suggested four dark areas which may be oceans of hydrocarbons’ These were given names. It was suggested that the Huygens Probe may in fact land in the 'Dragons Teeth Ocean'. This is based on it’s present planned trajectory. However all sorts of unexpected effects such as small errors in calculating the atmospheric pressure could have changed the expected landing site. In fact it landed on soft 'muddy' land.   Credit European Southern Observatory (ESO) Very Large Telescope(VLT) Paranal Observatory Atacama Desert.  Note that in view of later observations the concept of four oceans to explain the markings does not appear to be the true explanation of the markings. There may be small lakes on Titan but no really large expanses of liquid.

The North Pole

Large polar ethane cloud observed on Titan’s north pole

Report on 5 September 2006  'Cassini's Visual and Infrared Mapping Spectrometer (VIMS) has detected what appears to be a massive ethane cloud surrounding Titan's north pole. The cloud might be snowing ethane snowflakes into methane lakes below.'

The interior

Little is known of the interior .  It is thought that beneath the froze ice there may be a water ocean containing ammonia and methane clathrates.  Just as with Europa the question must arise as to whether there is some form of primitive life existing in such an ocean. Another interesting possibility about Titan is that it may have a layer of mushy ice beneath the crust which could give rise to some form of plate tectonics with subduction zones and ice volcanoes (cryovolcanism).

Future Explorations

The Cassini-Huygens Mission has proved that by working together in friendly co-operation, men and women of many nations can fabricate spacecraft capable of crossing the stupendous distances that separate the Earth from the planets of the Outer Solar System.  One day this century we shall return with air balloons or some other vehicles to explore the mountains and valleys of Titan.

In some long distant future time, after International Stations have been established on the Moon and Mars, men and women travelling in super-rapid spacecraft may land on Titan and dressed in warm and comfortable space-suits walk in the icy valleys and climb the frozen ice cliffs of Saturn's largest moon.

ESA Report 27 February 2007

 

27 February 2007  Photograph Credit Cassini NASA/JPL
During a near-polar flyby on 22 February 2007, Cassini's radar instrument took beautiful images of Titan's surface features – a big island smack in the middle of one of the larger lakes imaged on this moon so far, and dunes.
 
The island visible in the first radar image is about 90 by 150 kilometres across, about the size of the Big Island of Hawaii. It may actually be a peninsula connected by a bridge to a larger stretch of land. As you go farther down the image, several very small lakes begin to appear, which may be controlled by local topography
.

For more details see ESA Cassini Huygens web-site.

Latest news 11 August 2007 Edition of New Scientist

An article appeared in this week's New Scientist about the detection of sound on other planets of the solar system.  In particular it had a long section quoting Professor John Zarnecki on the very successful use of the microphone on the Huygens Probe.  The sonar revealed the lie of the land over an area of about 10000 square metres around the landing site confirming the photographic evidence.  It also went on to give quite a detailed discussion of the analysis of sound waves.  Sound is affected by atmospheric pressure, the nature of the atmospheric medium and even the size of the raindrops (methane rain in this case).  A radar instrument on the Cassini orbiter has now detected a number of  hydrocarbon lakes near the polar regions and future 'Huygen-like' expeditions may well target these regions.  here a great deal of scientific information may be obtained.  Investigations may even be carried out on 'methanefalls' as they splash down into the lakes.

TITAN DISCUSSION MEETING at ROYAL SOCIETY LONDON 3-4 December 2007

A discussion meeting was held at the end of December 2007 by leading scientists involved in the Cassini-Huygens mission to Titan and Saturn.    Here the emphasis was on the progress made since the landing of the European Space Agency's Huygen's Probe and the subsequent investigation's by instruments on board the NASA/ESA Cassini mother ship.

It was organised by Dr Jean-Pierre Lebreton, Dr Ingo Mueller-Wodarg and Professor Roger Yelle, all leading scientists in the Huygens Mission.  The evening of the 3rd December also saw a complementary lecture delivered by Professor John Zarnecki one of the chief investigators of the Huygen's probe and a leading scientist in the Open University.  He spoke to a packed audience and gave a stimulating account of the triumphant success of the Mission to Titan.

Titan -The Future

Both the Americans and the Europeans are already laying down future plans for the investigation of Titan.  Great curiosity is also being shown in the unexpectedly interesting smaller moon Enceladus.

People interested in the future are recommended to go to the web-site on the Tandem Mission, spearheaded by ESA but attracting collaborators from 155 International members from 11 European countries, the US, Canada, China, Japan and Taiwan).   Link to http://www.lesia.obspm.fr/cosmicvision/tandem/whatis.php

TANDEM is a large International collaborative effort, with 155 members from more than a dozen countries in the whole world. This ambitious mission will address several of the Cosmic Vision 2015-2025 call themes with orbiters, balloons, landers/penetrators and a state-of-the-art multitask payload to be delivered to the satellites around 2030.  Illustration by kind permission of  Cnudde@SIGAL.  This illustration is reproduced in the Tandem web-site and in the large poster on the mission displayed at the Royal society Discussion Meeting in December 2007

Dr Athena Coustenis of  LESIA Paris -Meudon Observatory submitted the poster at the Royal Society meeting

 

 

 The enthusiasm and energy that goes into space missions is shown by the Feasibility Study Report published on the web: web-site http://www.lpi.usra.edu/opag/TitanEnceladusBillionDollarBox.pdf  It was published on 30 January 2007 under the title Titan and Enceladus $1B Mission and prepared by Kim Reh of the Jet Propulsion Laboratory in Pasadena and Ralph Lorenz of the JPL and the John Hopkins University and their co-workers.  They too submitted posters to the discussion meeting at the Royal Society meeting and discussed the possibilities of future missions to Titan and Enceladus.

The three illustrations shown below are published in the feasibility report.  Full credit is given to the authors of the report and to NASA and JPL

 

 

 

 

 

 

It should be pointed out that the sand dunes are of course made up of ice and organic materials such as tholins (and obviously not silicate rocky debris).

 

 

 

The Solar System