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NARRATOR (JACK FORTUNE): This is the story of the most ambitious un-manned space project ever launched - its destination Saturn. The mission: to investigate this hauntingly beautiful planet and its enigmatic rings. But the climax of the mission will be Saturn's largest moon, Titan. The hope is that by exploring this alien world are will get closer to answering that great scientific mystery - the origin of life. Tonight, Horizon follows this fantastic voyage across the solar system to find out how it all began.

June 30th 2004. The World's press have gathered for news of the most critical part of this 3.2 billion dollar mission. The Cassini spacecraft is scheduled to go into orbit around its target - Saturn. The slightest hitch during this complex manoeuvre and the entire mission will be lost.

MALE VOICE: We are slowing down.

CAROLYN PORCO: You can image how anxious some of us were... knowing that it all hinged on one ninety minute period, where we would have to perfectly just slip into orbit.

MALE VOICE: The Doppler has landed - cheering

NARRATOR: This moment was the culmination of 14 years preparation and a 7 year trek across the solar system. But the real highlight was when Cassini started to beam back its images from over a billion miles away.

INTERVIEWER: How're you doing?

CAROLYN PORCO: Oh it was fantastic. It was just great.

CHARLES ELACHI: You wait years for this kind of a moment.

MALE VOICE: Citizens of the Earth - I would like to present the majestic rings of Saturn.

NARRATOR: This remarkable spacecraft had travelled over a billion miles towards the outer reaches of our Solar system. To a giant swirling ball of gas over 750 times larger than the Earth. The mysterious world of Saturn.

Cassini's story can be traced to the launch of a different mission 27 years ago - the voyager deep space probes.

When they flew past Saturn they provided tantalising glimpses of this distant world. Saturn's giant rings were seen closer than ever before revealing details that were completely new and unexpected.

CAROLYN PORCO: Before Voyager got there, we knew very little about the rings. There wasn't a great number of people even studying the rings. Voyager got there and found this bewildering array of structure in the rings, and people set about trying to explain it right away.

NARRATOR: It had always been assumed that the rings were as old as Saturn itself. But the new information sent back by the probes pointed to something very different.

LARRY ESPOSITO: We saw processes going on in the rings that were too fast, that would have gone to completion long before the age of the solar system, the age of the planets so that Voyager information showed us the rings must be created much more recently.

NARRATOR: Voyager begged the question: if the rings are not as old as Saturn, how old are they? And how did they get there? And Voyager was to uncover yet more mysteries. For the first time detailed images were taken of Saturn's many moons. They showed ancient cratered surfaces. But one stood out, Saturn's largest moon Titan. It was unlike any moon that had ever been seen - it had a thick almost Earth-like atmosphere. But frustratingly its surface was shrouded by a layer of orange cloud.

CHARLES ELACHI: We saw this fuzzy ball, and the immediate reaction is, what's below those clouds. You know, what are these clouds made of, what is hidden behind that layer?

NARRATOR: Titan would remain a mystery. Voyager had to move on - out towards Uranus, Neptune and beyond. Leaving behind it more questions than answers and scientists desperate to return.

LARRY ESPOSITO: The combination of the spectacular structure in the rings, the youthful processes in the rings, the hazy atmosphere of Titan just left every scientist with a great curiosity to explain those things that we had seen with the Voyager fly-bys. Immediately there was a feeling that we had to return to Saturn and stay there for a longer time.

NARRATOR: So in 1990 work began on a spectacular new spacecraft. The result of a unique co-operation between NASA and European Space Agencies, the Cassini probe would carry the most complex array of instruments ever launched into space. It would be capable of measuring everything from magnetic fields to minute particles of cosmic dust, but at the heart of this array of instruments were the eyes of the mission - the two cameras.

CAROLYN PORCO: One is a very long focal length, very high resolution, but you get a little postage stamp-like coverage. And so you want to also carry a camera with a larger field of view, shorter focal length that covers a greater amount of territory, so you can put your little postage stamp coverage in context, in geological context.

NARRATOR: Cassini was also loaded with a powerful radar designed to do what no camera can and punch through Titan's hazy atmosphere to reveal the surface below. But Titan has so intrigued scientists that they decided to send in a separate probe for an even closer look. That probe is called Huygens after the man who first discovered Titan.

JOHN ZARNECKI: Rather than viewing from a distance, we're going for the broke, Huygens is actually going to plunge through that atmosphere and take in situ measurements. We want to know exactly what the composition of the atmosphere, what are the gases which make up the atmosphere, and we'd also like to know about meteorology or weather in Titan's atmosphere.

NARRATOR: This bold plan had one major draw back - the resulting craft was massive.

BOB MITCHELL: The Cassini spacecraft is the largest inter-planetary satellite that NASA has ever built and launched. At launch it weighed nearly fifty eight hundred kilograms

NARRATOR: The big problem was how to get this five and a half tonne leviathan into space. The most powerful rocket on Earth, the mighty Titan IV was selected for launch delivering over 3.9 million pounds of thrust. But even this would not be enough. Because this massive space craft didn't just have to get into space - it had to travel over a billion miles, all the way to Saturn. The only way to travel this vast distance would be with a little help from the planets.

LARRY ESPOSITO: The energy that we needed to get out in the solar system, out to the planet Saturn had to be supplemented by, partially provided by gravitational encounters with the planets. The important thing is to gather energy from the gravity of the planet you're flying by.

NARRATOR: So Cassini was routed via the Earth's nearest neighbour Venus. This planet's gravitational pull would accelerate Cassini, increasing its speed by over 8000mph. But this still would not be enough. Cassini would return for a second boost from Venus. The Earth would then accelerate Cassini flinging it out further - towards its next rendezvous - Jupiter.

The probe would clock up a speed of 50,000 mph before reaching its final destination - Saturn. October 15th 1997: Cassini was blasted into the night sky. All the planets it needed for its trip to Saturn were in perfect alignment. An event that would not re-occur for over 600 years. What lay ahead was an epic 7 year journey across the solar system. When the probe swung back past the Earth the radar was checked out. It scanned a huge swathe of South America - and everything was in working order. Cassini seemed to be operating flawlessly. The Europeans also decided to test out the radio link between Huygens and Cassini. This was when things started to go wrong. Huygens is designed to beam all its data up to Cassini as it plunges through Titan's atmosphere.

JOHN ZARNECKI: The Huygens probe itself doesn't have enough power, and it doesn't have a large enough dish to transmit its data, the scientific data that it collects on Titan, directly back to the Earth. So what will happen is that it uses the Cassini space craft as a data relay.

NARRATOR: The test was designed to make sure that Cassini could receive all the data from Huygens. But when the results came back they were alarming.

JEAN-PIERRE LEBRETON: We were expecting to receive all the simulated data. Unfortunately we did not receive very many of those data. We lost, well, it's - we lost maybe ninety per cent of the data, sometime even all of the data, so...

NARRATOR: If Cassini could not pick up the precious data from Huygens as it travelled to Titan there would be no results, no pictures - nothing. The entire mission would be lost. The Huygens team called a meeting to break the news. Imaging specialist Marty Tomasko had spent over ten years building the camera for Huygens - he couldn't believe what he was hearing.

MARTY TOMASKO: They said we've preformed the test and we didn't get any signal but the test accomplished all of its objectives and some of us were sitting around the table saying what exactly are you trying to sell us? You know you've accomplished the objectives of conducting the test but you've actually succeeded in proving the thing is not going to work.

NARRATOR: But the Europeans were hoping there might be a simple explanation.

JEAN-PIERRE LEBRETON: Maybe the test is wrong, this is the first thing you say, oh, the test is wrong, we have done something wrong so everything is good with the hardware, no problem, it has been tested on ground so the test must be wrong.

NARRATOR: But the test was not wrong. 6 months of painstaking research revealed a tiny flaw in Cassini's receiver.

JOHN ZARNECKI: It was enough to essentially put the link between the two out of alignment. It was as if Huygens was transmitting on Radio One, on one frequency and Cassini was receiving on Radio Two, a slightly different frequency. So this was potentially disastrous.

NARRATOR: Repairing the receiver was impossible. It was out in space over 300 million miles away.

JEAN-PIERRE LEBRETON: There was no way we could repair so we had to find a new mission scenario which would allow us to live with this problem but still to recover the - the whole mission.

NARRATOR: After months of research an ingenious plan emerged. They couldn't retune Cassini's receiver but they could shift the signal it was receiving using a basic principal known as the Doppler effect. If they could slow Cassini down, it would pass through the radio waves from Huygens at a slower rate. This means that the radio waves would hit Cassini at a lower frequency. This lower frequency signal could then be picked up by the faulty receiver.

JEAN-PIERRE LEBRETON: All in all it took us six months to find a solution, but it took us two years to design all the detail of the solution and to test it. We are now recovering the full Huygens Mission, we are not going to lose any science, so it's a very successful recovery.

NARRATOR: Scientists were now confident that Huygens had every chance of sending back its precious data when it finally reached Titan.

As a new millennium dawned on Earth, Cassini had crossed a billion and a half miles of space and arrived at Jupiter, the Giant of the solar system. Twice a massive as all the other planets combined its powerful gravitational field would give Cassini its final boost. Scientists waited anxiously, because Cassini's cameras faced their biggest test yet. Jupiter's majesty was revealed as never before - its swirling clouds and icy moons were seen with breathtaking clarity. But Cassini had to move on across another 500 million miles of space to its final destination.

For imaging team leader Carolyn Porco, the Jupiter pictures were a triumph. But her real goal was always Saturn - she has devoted her entire career to studying it and it is now part of her life.

CAROLYN PORCO: To know that we can know so much about our solar system and about our cosmos makes, for me, life meaningful. It's very much like being in love, it's very much that kind of a relationship where you want to know more and you want to be one with the person you're in love with or the topic that you're studying. It's a connection, it's really a connection and for me, it's like being allowed a glimpse of the miraculous.

NARRATOR: By the spring of 2004 Cassini had closed in on Saturn. But just before contact, mission planners had calculated a precise course to send the spacecraft past Phoebe - Saturn's curious outermost moon. Almost all of Saturn's moons orbit in the same direction around its equator- but not Phoebe.

BOB BROWN: It's actually moving in a direction backwards to what you would expect and it's also orbiting in a plane that's very highly inclined to the equator of Saturn and satellites, if they form naturally around the planet are not expected to be in a plane in - in any other plane except for the equatorial plane of the planet so very early on when people figured out Phoebe's orbit, it became clear that it was unlikely that Phoebe formed as part of the regular stable of satellites that are around Saturn.

NARRATOR: If Phoebe was not formed along with Saturn it must have come in from elsewhere and been sucked in by Saturn's gravitational field. But where had it come from? Scientists believe that there are two options.

BOB BROWN: One is the asteroid belt between Mars and Jupiter where things are made of rock, probably not dramatically different than the rock we have here.

NARRATOR: The other is a much more distant place called the Kuiper Belt - a mysterious band of rubble left over from the formation of the outer planets. These are the most ancient objects in our solar system.

BOB BROWN: Those objects are made primarily of ice, so they have dramatically different composition; everybody knows the difference between a rock and the stuff you put in your drink to keep it cool and if you can figure out a way to tell that difference from a long way away which is what we have to do with spacecraft then you can start to get a real handle on where Phoebe came from.

NARRATOR: Until now all that scientists have had to go on is this picture; taken by Voyager 23 years ago. But this time Phoebe was in the cross-hairs of Cassini's powerful cameras. Picture after picture returned with unprecedented detail.

CAROLYN PORCO: We buzzed Phoebe, okay, we came within two thousand kilometres of its surface. You could, reach out and touch it, is what it looked like. So it's very exciting. We saw features that were, were 30 metres across.

NARRATOR: At last Phoebe was giving up her secrets. The images revealed an ancient surface pitted with craters caused over billions of years. But to solve the mystery of where Phoebe had come from scientists needed to work out what it was made of. And that meant turning to a different piece of equipment.

The technology Cassini used to reveal Phoebe's origins is aboard this aeroplane. It was developed to identify different varieties of rocks at high speed just by flying over the land. Previously that was a task that could only be done slowly - by geologists painstakingly collecting samples by hand.

AMER SMAILBEGOVIC: To us and our crude sensors called eyes, both of these rocks are very similar, only trained geologists or somebody with lots of experience can tell you what kind of rocks they are. However, imagine having some kind of special goggles that you could put on your eyes and that they would make these rocks not be so drab and white but stand up with the things that you would actually like to know. That even to the layman they would say, this is the rock you want and this is the rock you don't want.

NARRATOR: The technology that performs this remarkable feat is called a mapping spectrometer. It works by measuring the different frequencies of light reflected by the rocks below. Every mineral reflects light at its own unique set of frequencies. The spectrometer can spot these differences and interprets them as different colours.

The data from the spectrometer is then used to build up a multi-coloured 3-D map of the area.

The result is a complete picture of the mineral content of the terrain - all achieved without anyone needing to take a sample.

The same equipment has been adapted for Cassini's trip past Phoebe.

BOB BROWN: We've taken the concept, wrapped it in a wrapper that allows it to operate in space, put in on a spacecraft and flown it to Saturn. Now that is kind of an understatement because it costs sixty million dollars and took seven years to build the instrument.

NARRATOR: As Cassini approached Phoebe, the spectrometer got its chance to solve the riddle of Saturn's wayward moon. The results were better than anyone could have hoped.

BOB BROWN: Actually we were blown away by data we got on Phoebe. We found water ice, we found organic materials, we found carbon dioxide, which was a bit of a surprise. We found poisons, cyanides - all of those things put together really painted a very nice picture in the sense that it was clear after we looked at the data that this object does not come form the asteroid belt.

NARRATOR: Cassini had proved once and for all that Phoebe had come in from the cold outer reaches of the solar system. This was scientists' first glimpse of these primordial objects decades before any mission could ever get there. But Phoebe was just a taster - a preview of what was to come.

June 30th 2004: mission control had piloted the Cassini spacecraft across 2.2 billion miles of space and it was still right on target - and fast approaching its destination - Saturn. What lay ahead was that great enigma - the riddle of Saturn's rings. Scientists understand so little about them they still have even the most basic questions to answer.

CAROLYN PORCO: The questions that we scientist have about Saturn's rings are the questions that an ordinary person might be moved to ask when first seeing them, you know. What caused them? How did they get there? How long have they been around? How long are they going to last?

NARRATOR: Answering these questions is one of Cassini's prime objectives. But to do this, it first had to get into orbit around Saturn and that meant passing between the rings. The rings are chaotic and dangerous. Made up of billions upon billions of hard rock like particles.

LARRY ESPOSITO: All the ring particles, billions and billions of them are in orbit around the planet Saturn and they're moving at quite a clip - something like ten kilometres per second. Faster than a high-speed bullet. If you were in Saturn's rings you would be in a mass of particles that were bumping into each other and rolling over each other and if you were a ring particle you would get bombarded from one side and then from the other, as one particle bounced of another one around you.

NARRATOR: To carry out its mission Cassini risked being torn apart.

LARRY ESPOSITO: Even a very small particle could be the end of Cassini, if it hits a particle as small as a grain of rice that would be enough because of the high speed at which it's moving to end the mission.

NARRATOR: At Mission Control tension was building as the high risk orbit insertion manoeuvre began.

BOB MITCHELL: Saturn orbit insertion was a bit of a nervous time for us. There were a lot of things that had to work right. The consequences of it not working would have been pretty serious.

NARRATOR: The rings were not the only danger that Cassini faced. To get into orbit it also had to slow down. That meant firing its main engine - any malfunction and Cassini would simply fly past - lost forever in the void of space.

CHARLES ELACHI: That engine had not been used very frequently over a period of seven years, that makes you nervous. You know, it's like you have a car, a brand new car that you put in the garage, and every once in a while, you turn it on, and then you have an emergency, and you get in the car, and you turn it on, it'd better work.

NARRATOR: The sequence began at seven thirty six pm. First Cassini rotated, to use its giant antenna as a shield to protect it when it passed between the rings. All eyes were on a signal sent out by the probe's tiny auxiliary transmitter. Only if the signal flattened out at the bottom of the graph would they know if Cassini had survived. A 3.2 billion dollar mission and 14 years of work all hinged on this one moment.

MALE VOICE: The Doppler has landed - Roars of excitement.

NARRATOR: Cassini had arrived. When the images returned Saturn was revealed as never before.

CAROLYN PORCO: I just don't know what to say, I'm speechless.

CHARLES ELACHI: Oh absolutely exciting, this is the culmination 22 years of effort and just seeing the lord of the rings in its big glory... We are amazed about the detail we are seeing and the sharpness in the rings. You wait years to have this kind of a moment.

NARRATOR: Despite these remarkable images the fundamental question of the age of Saturn's rings remains unanswered. Some hope that this enduring puzzle might be solved by taking a very close look at what the rings are made of.

LARRY ESPOSITO: The rings are made of ice. Just like the stuff you've got in your ice cube trays and almost a hundred per cent pure water ice with some small contaminants.

NARRATOR: These contaminants are the key to finding out the age of the rings, minute traces of dust that come from meteoroids. The basic principle is simple - the older the rings are the more they will have been bombarded and so the dirtier they will be.

LARRY ESPOSITO: The pollution is sort of a like a clock because we're pouring material in on top of the rings and it's dark, non-icy material so the level of darkness in the rings tells us something about their age.

NARRATOR: So to discover the level of pollution in the rings Cassini's spectrometer took these images. What they show has surprised scientists.

LARRY ESPOSITO: The spectacular range of structures, the high structure in the rings with reds and blue and aquas, that was something that was completely unpredictable.

NARRATOR: The images show cleaner ice in shades of blue; the heavier contamination in red. The analysis on this is not yet complete but these new spectrometer images seem to suggest an intriguing possibility - that perhaps Saturn's rings were not all formed at the same time.

LARRY ESPOSITO: It's definitely the case that there's a gradient in composition across the rings so that the rings are less icy on the inside and more icy on the outside. As we go to the outside the particles become younger and fresher.

NARRATOR: So it appears that the inner rings shown in red are in fact older, and that somehow the outer rings have been made more recently. To work out exactly how this is happening will take several years of observations. But now Cassini is safely in orbit the scientists will have all the time they need.

But there is a whole other aspect to Cassini's voyage - one that has not yet begun - It's encounter with Titan - one of the great mysteries of our solar system. It's thick atmosphere captivates scientists as it might mean that Titan in some way resembles the Earth.

CAROLYN PORCO: Whenever we humans think that we might be approaching something that is vaguely similar to Earth, we get very excited about it. The prospect of something familiar, but yet so distant, and so strange is a very exciting combination.

NARRATOR: Trying to figure out what this distant moon will look like has become an obsession for planetary scientist Dr Ralph Lorenz. He has spent the past 15 years trying to piece together all the scraps of information available on Titan to build up a picture of this mysterious place. And he believes it is a world that shares many features with our own. But on this distant moon things are also very different.

RALPH LORENZ: The landscape may be strangely familiar much as there is on Earth there may be a cycle with the rain and rivers and streams. Titan is so cold that methane which is a gas on Earth can condense into a liquid and freeze as a solid on Titan. They may have lakes but the lakes are made of - lighter fluid.

NARRATOR: If Dr Lorenz is right the methane will also form familiar clouds but it might turn the sky a very unfamiliar green. We might see methane rain falling from these clouds but because Titan is smaller than the Earth it has less gravity this rain would be unlike any we have ever seen.

RALPH LORENZ: The balance of forces that holds a raindrop together is a little bit different on Titan because the material is different and so the raindrops could be rather larger but on Titan with its thick atmosphere and its low gravity, these large raindrops would fall maybe ten times slower than raindrops do on Earth. The rain falls so slowly, it just evaporates before it gets to the ground. That may be quite common on Titan.

NARRATOR: The picture of Titan that emerges one of a truly alien world - a place where huge rain-drops fall gracefully through a green sky, a place with lakes and streams made from lighter fluid. And stranger still the entire landscape is made of water - frozen hard as rock. But for the moment this picture is a very well educated guess as no one as yet been able to take a clear picture of Titan's surface. Because this mysterious moon is veiled by a thick layer of orange cloud.

But Cassini carries two powerful instruments designed to defeat this layer of haze. One is Cassini's radar scanning over a quarter of the moon - it will send back the first accurate images of Titan's surface. The second is the European built Huygens probe. Huygens will separate from Cassini and plunge beneath the clouds carrying its own unique camera. Imaging specialist Marty Tomasko will have no second chances - the Huygens probe will be active for just 180 minutes as it descends - so it's important that his camera doesn't miss a thing.

MARTY TOMASKO: So what we were trying to get is kind of the skydiver's eye view because if you were outside the probe and falling down through the atmosphere we don't want to land near some interesting object like the Grand Canyon and not know it's there.

NARRATOR: So the plan is to spin the probe as it descends giving the camera a full 360 degree view. But Tomasko has also given the camera 3 lenses to ensure that it has absolutely no blind spot.

MARTY TOMASKO: We have three fields of view, one that comes out this window and looks out towards the side, one that comes out this window and looks down at intermediate angles and one that looks almost down straight towards the ground and those three images are taken together and as the probe rotates we take a series of twelve of those over a few seconds or a few minutes and we plan to put those together to make panoramic mosaics of the surface of Titan during our decent.

NARRATOR: These panoramic mosaics were created with the same camera in a test over the Arizona landscape. By putting them together a virtual world can be created. The hope is that the next time the camera opens its three eyes it will be peering down on a new world - Titan. But Titan is more than just a curious alien landscape. It is a place that perhaps holds the key to one of the greatest mysteries of the universe - the origin of life.

BOB BORWN: For me one of the most important questions to address is where did I come from? This rock is not conscious and I'd a heck of a lot rather be me than this rock but the same stuff that's in this rock is in me it's just organised in a way to contain enough information so that that stuff can turn around and say, what is this? How did it get here? And, oh, by the way, how did I get here? How did you assemble this simple stuff into something like me and allow me to ask those questions?

NARRATOR: Earth today is teeming with life - it has taken over the entire planet. Bizarrely this makes the Earth a very bad place to study how life first emerged from the primordial organic chemicals that first covered it.

JONATHAN LUNINE: It's very difficult to use the Earth as a laboratory for understanding how life began. Life eats all of the organic molecules that are present on the Earth today. If we go to the laboratory and try to simulate how life began, we have limits on time and space; a laboratory experiment might be this big; a laboratory investigator might work for two or four or ten years perhaps. No more than that. We really need a place where organic evolution is happening on a planetary scale, over billions of years but is not being ruined by the presence of life.

NARRATOR: So for many years scientists have been looking for a place that shares the same primordial chemistry as the early Earth.

JONATHAN LUNINE: If you look at our solar system, there are only four bodies that have atmospheres and are actually solid bodies themselves: The Earth, Venus, Mars and Titan. Venus is just so hot that one can melt lead on the surface, there's - there are no organic molecules. Mars today is very cold, very dry, very thin; not a good place for organic molecules. And so we're left with Titan.

NARRATOR: Titan has all the ingredients to create complex organic molecules - methane and nitrogen. On the Earth, billions of years ago, these simple chemicals somehow combined to form the pre-cursors to life. Scientists believe that these same chemical reactions, the first vital steps on the road to life, are occurring today high in Titan's atmosphere.

JONATHAN LUNINE: The purpose of the experiment is to simulate the chemistry that makes complicated molecules from the simple gases in Titan's atmosphere and so here we have nitrogen which is the primary gas in Titan's atmosphere and we have methane over here. And these gases are mixed together and they're run through tubes and then they end up down here which is an electric discharge and this simulates the energy that the sun provides to power the chemistry.

NARRATOR: The Sun's rays break up the methane which then recombines to form a set of dark orange chemicals known as tholins. These tholins form the thick orange clouds that shroud Titan and hide its surface. But tholins can make more than just a haze. With just one extra ingredient they form one of the key components of all living things - amino acids.

JONATHAN LUNINE: If we were to apply what is the essential ingredient of all life which is liquid water then we may well make some amino acid which is the building blocks of life and that's the really exciting thing about tholins.

NARRATOR: But the surface of Titan is at 174 degrees below freezing - far too cold for liquid water. However, scientists believe that Titan's interior may be warmer and that there could be a layer of liquid water under the surface. It is possible that this liquid could rise upwards through volcanoes.

BOB BROWN: On the Earth volcanoes belch rock. On Titan volcanoes most likely belch water. And liquid water has an important role to play we think in helping to bring about the rise of life.

NARRATOR: While any water on Titan would eventually freeze, it might remain liquid long enough to allow the formation of amino acids. So, with tholins in its atmosphere and the possibility of water, Titan might just have all the ingredients to make the primordial soup from which life first emerged. At 2 am on Christmas Day, three explosive bolts will fire and Huygens probe will be pushed away. 22 days later it will slam into the upper atmosphere. A series of parachutes will then slows its descent.

And only then will the charred heat shield be ejected. The chemical analyser will then search for signs of complex organic chemistry. At last Huygens' camera will get the first view of Titan's surface. Will Huygens discover streams of liquid methane? A rock hard surface of frozen water ice? Or a soft sludge of organic chemistry warmed by a nearby volcano? Until January 14th 2005, no one will know.

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