Titan: Exploring the origins of life

For starters, Titan's atmosphere is packed full of complex organic molecules. When sunlight (even as faint as the sun is all the way out around Saturn) travels through Titan's atmosphere, it creates all kinds of interesting chemicals from the methane and ethane already there. We know that there's acetylene, ethylene, and hydrogen cyanide in Titan's air, the last of which was a very important molecule (we think) for getting life started on Earth. And there's plenty of other gook floating around Titan's atmosphere, including brownish, smoggy hydrocarbons that may actually precipitate and rain down on the surface into viscous, oily puddles. In short, the chemistry on Titan is a lot like what we think the early Earth was like.

One of the key requirements for creating life, it seems, is the presence of a liquid. In order for life to begin, large, complex molecules have to be given the chance to mix around and interact with each other. If everything is frozen solid in ice, there's not much mixing to be had. If there's nothing but gas around, the molecules don't have much time to hang on to each other as they blow past each other in the air.

But liquid is just right for those kinds of interactions. In a liquid, molecules can mix, interact with each other, maybe even form longer, more complicated chains. With enough time and the right circumstances, the molecules may even learn to replicate themselves from smaller bits and pieces floating around in the muck. Let sit for a few million years, and lo and behold, you get DNA, or something similar. Life has begun.

Now, Titan is way, way too cold for liquid water to exist (at those temperatures, water is about as solid and dense as granite). But here's where the super-cold temperature may actually prove to be an advantage.

Given very low temperatures and high air-pressure, methane and ethane can exist in liquid form. Liquid methane, especially, has a lot of the same chemical properties as water, and may provide a similar environment for life to take hold. Recent observations suggest that conditions may not be quite right for liquid methane to exist on Titan's surface, but liquid ethane with dissolved methane in it is still a strong possibility. And that may just do the trick.

Still, scientists have found out that defining exactly where life begins is far more tricky than they first thought. We know of lots of complicated molecules, some of which can even replicate themselves, but we wouldn't call them alive. But somehow, life arose from them. Where is the cut-off, and would we even recognize the very first beginnings of life if we saw them on Titan, or another world?

It's an interesting question, and one that as led NASA to give the exploration of Titan a high priority. In 1997, NASA launched the Cassini spacecraft to explore Saturn, as well as its mysterious rings and moons. It's taken quite a while to get out there, but 2004, the probe will arrive at its destination and begin a many-year survey of the Saturn system. One of the most exciting aspects of the mission will doubtlessly be the release of the Huygens probe, a miniature laboratory that will be dropped from Cassini and sent down to plunge through Titan's hazy clouds. On its descent, for a mere three hours, the probe is scheduled to analyze Titan's chemistry, sniffing and tasting the various cloud layers before it touches down (on a cold dead surface? Sinking into liquid ethane oceans?) and ends its mission.

We're expecting a view not only of a distant, exotic world, but a glimpse back in time to what we may have looked like billions of years ago.

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