Titan is a world that is rich in organic chemistry. It has an atmosphere with, abundance of CH4, of methane. It has lakes of this methane. What it doesn't have, of course, is water. The water is frozen in the form of ice, on the surface. This has led some people to speculate, well maybe if you had an impact that, that smashed into the surface of Titan. Excavated a big crater, heated things up for thousands of years as it was cooling down, you could have pockets of liquid water. Take those pockets of liquid water, now add in all those hydrocarbons, and indeed you have a nice warm soup, sort of, and it's all just like if, things that might have happened. And of course, these then freeze out over time. And you might be left with little pockets, where biology or pre-biological chemistry occurred. It's a possibility. To my mind, that's a bit of a desperate possibility. If you're looking for little pockets where things might have happened rarely, you're going to have a hard time finding them and studying them when you do. What you really would like to know, is, is there something happening on Titan right now? Is there some possibility that we have weird life on Titan? This weird life would be based on methane rather than water, because there is no water. And it would have to find some way to get energy. Now Titan is a very cold environment. The, the temperature is 94 degrees, Kelvin, 94 degrees above absolute zero. Chemistry doesn't take place very quickly at these temperatures, so it's hard to imagine very much going on. The one place where things do happen is the atmosphere. Why, why do things in the atmosphere? Because of all this methane, sunlight coming in, breaking apart the methane molecules to CH3 and Hs. These very quickly react, these are radicals, they very quickly react, and they make things like C2H2. C2H2 is acetylene, and, and make things like C2H6, which is ethane. Often if I say the word acetylene, people will get very excited, because they think, oh, acetylene is very, very energetic. Acetylene is explosive here on the Earth. Acetylene is what was used for many years in miner's lamps. If you take acetylene and you combine it with water, and you light it, you get either a nice explosion, or you can get a nice confined flame that you can use for your miner's lamp for a long, long time. For that explosion, though, you need oxygen. I think I said, you combine calcium carbide with water to make acetylene, which you then combine with oxygen to make the flame in the miner's lamp. Titan, no oxygen, no flames from the settling. But what do you have? You can take C2H2 and combine it with something you do have which is H2, and this is a reaction that creates energy. Where did that energy come from? That energy came from sunlight. You could almost claim this is some interesting form of photosynthesis. You have sunlight breaking these molecules apart, and then you recombine them to re-extract the energy out. It is absolutely a viable source, of energy, on the surface of Titan. There was a fun paper describing this possibility by Chris McKay. And, one of the reasons I like this paper so much, he didn't just speculate, oh gee, this could really happen. He showed that a consequence, if you had abundant life on the surface of Titan that was eating the acetylene, combining it with molecular hydrogen to create energy. It would very quickly lead to the consumption of much of the hydrogen that would be around at the surface. And the reason that's interesting is because this was just as the Cassini Huygens probe was about to land on the surface of Titan. The Cassini Huygens probe parachuted through Titan's atmosphere and landed on the surface. It was easy to parachute through Titan's atmosphere because Titan's atmosphere is so big and so thick, it was like landing on a pillow. Went through the atmosphere, measured the composition of the atmosphere, went down, including things like hydrogen. What did it find? It found, well, okay, it's complicated. So here's a plot of the going down onto the surface of Titan, here is the surface of Titan radial distance from the center, so the center of Titan. The radius of Titan is 2600 kilometers. And this is the upper atmosphere, as the Huygens probe descended down and measured the abundance of things like H2, N2, that's the most abundant thing in the atmosphere, just like our own atmosphere. There's the methane that we know is there and argon as it goes down. So, as you go down everything increases as you go down, the density of the atmosphere increases as you go down and then, just below this region. Here's the temperature here. This little spot that you barely can see, right here. This is, this is where all the action is, this is called the tropopause. That's because the temperature pauses right there. Temperature suddenly starts to increase again as you go down after a lot of decreasing. That's also the place where the clouds occur. All of this stuff, this little, tiny region below here is the troposphere. It's equivalent to the region in the Earth's atmosphere where all of our weather occurs too. So this would be the stratosphere of Titan, up through here, and the thermosphere all the way up through here. So pay attention just to this little bitty slither down through here that I've drawn over so you can't see. And what they've found, which is what this arrow is supposed to be indicating. What they found is that there is a sink of hydrogen, at the surface. That as much hydrogen is escaping into space which it does because Gene's escape. As much is escaping into space as is being consumed at the surface. Maybe consumed is a bit of a loaded word there. Where is that molecular hydrogen going? Well there could be some chemical reaction that's going on that removes it that no one has thought of. That could be caves of hydrogen underneath the surface, that doesn't seem very likely. It could be that there are acetylene and hydrogen microbe eating microbes that are right at the surface that are eating all of that hydrogen. This is the way science is supposed to work. There was a prediction from McKay that there would be a depletion of hydrogen on the surface if there was life. There was a measurement that found exactly that, and well, people aren't actually convinced that that's what's going on. There are reason why they aren't convinced, and those are good reasons. The reasons, again a lot to do with the, the temperature of Titan, at 94 degrees Kelvin, chemistry occurs so slowly, that it's very difficult to imagine microbial life evolving or even thriving on there. The fact that there's no liquid water, but there's liquid methane instead makes a lot of people very uneasy. And the fact that we often make these measurements of things, compositions and atmospheres, and can't quite match them exactly right. Yes, it's true that this is exactly the effect that McKay predicted. But it seems likely that there's some other explanation going on. Or there's not, maybe there are hydrogen and acetylene-eating bugs on the surface of Titan. How would we ever find out? I'm not sure, that boat on the lake would probably make some very nice measurements to tell if something is going on, but that boat on the lake is not going to happen. Land on the surface and collect stuff, that's not going to happen anytime in my lifetime, probably not yours either. I think that most likely Titan is going to have to remain this mystery for a long time to come. It's a long ways away. It's hard to explore the outer part of the solar system, on human time scales. It's important, though. You know, we have the idea that Mars might have had life and it might have been contaminated from the earth. Europa, one could imagine missions that would eventually find out if there's life-like things on Europa, or, or Enceladus. And those are water based life and those would be fascinating for showing us that perhaps life could evolve in other places. If we found life in one other place, we would know right away that that was telling us that life is pretty easy to form if you have the right conditions. What about on Titan? That would blow the lid off the idea of life. That would say that not only does life form in conditions that we think of as habitable. But life finds a way to form in conditions that are even only vaguely habitable. It's fun to think about. We're not going to really be able to come to any conclusions about Titan any time soon. But it's a place that will continue to be intriguing, and we'll continue to try to get as much good data as we can over the years to learn what's going on there.
