Mike Brown's Planets: Titan

Showing posts with label Titan. Show all posts

The end of the fall

The fall term always gets a little overwhelming, as classes get into session and lectures need to be written, problem sets graded, exams created. I have an amazingly long backlog of things about which I want to write at this point but which I have not yet had the time to even get started. To top things off, my life appears to be changing forever. Most of these pieces get written on weekend afternoons while Lilah is napping. But the days of napping appear to be coming to a close.I understand intellectually that this is likely, after all, few 10 year olds nap, but I had never really stopped to think about the effect on my life. It’s not all bad; being able to pondering going out to do something with Lilah in the afternoon could be quite fun! But it will definitely gobble up my quiet afternoon writing time. But, today, after a late Halloween night and a no-doubt sugar-induced-early-morning wakeup, Lilah is currently snoozing away and I am going to now type as quickly as possible. Ready? Go! (Halloween? Yes, I started writing this almost a month ago, giving a perfect demonstration of the point I am trying to make.)

Back at the end of August I asked everyone to review my paper on Titan fog, and, to my surprise, many people took the task extremely seriously. The paper was discussed in classes and in on-line forums and was stared at by many eyes. If you recall back in August one of the reasons for attempting this open review was the fear that having only a single official reviewer leads to a huge random factor as to whether or not you will get anything useful out of the process. In this case, I have to say that the official review was pretty difficult to decipher. The reviewer commented on a few typos, complained about the location of the references, and said that the paper was generally incomprehensible.

Incomprehensible? Now, I will admit to having written papers that are incomprehensible before (how about this one; I can barely understand it myself 20 years later), but I actually thought that the paper was pretty clear. What’s more, of the many comments I had gotten from outside the official review process, no one had quite said “incomprehensible.” So what was going on here?

I reread the paper several dozens of times, and reread all of the comments that I had gotten, and realized, I think, the source of the problem. I think I was much too terse in my explanation of what I had actually done. Sure, I discussed fog and its discovery in gory detail. But I perhaps did not do a great job of describing how I really sorted through all of the data to find fog. It’s a pretty crucial step. If you don’t provide enough details in your paper that someone else could come after you and reproduce precisely what you did, you have failed an important point of having a paper in the first place.

One reason for describing all of this poorly was that the real process was actually quite different from the way I attempted to describe it in the paper. The real process consisted of this: I was looking at a bunch of pictures of Titan and said “Whoa; what the heck is that?” That turned out to be fog. I suspect that many discoveries are made that way, but if you read scientific papers you will rarely learn that fact. If you read my paper, you will find something like “Fog is very important so one fine day we decided to go look for fog on Titan. And we found it.”

OK, partially this description is true. After the first few times of accidentally seeing the fog we did, one fine day, systematically search through the entire data set. But that description was all pretty muddled.

The solution was a nearly complete rewrite of the paper. Had I just gotten the official review I would have fixed the typos and reworded a few things here and there and wondered what the heck the reviewer was talking about, but with the strength of the large number of comments, I could really tell what people were seeing and reading and I could make it significantly better. At least I think it is. But don’t take my word for it. Remind yourself of the first version, here. And now go read the new version here as it is about to appears in this week's Astrophysical Journal Letters. You still will not read the new version and realize that the real way we found fog is that we stumbled on it accidentally, but you will at least, I think, have a better idea of precisely what we did and how we did it. Want to go find fog yourself? I think the roadmap is now significantly more clear.

My conclusion from this experiment? I can’t tell you whether this system will always lead to such dramatic improvements in the quality of a paper, but in this particular case there is no doubt that when you read the two versions of the paper and you note any improvements almost all of those improvements came from the open review, rather than the official review. All of the comments that were sent to me were incorporated in one way or another. And for that, I would like to say a hardy THANK YOU to everyone.

But wait, there’s more!

Fresh on the heels of the Titan fog paper, I have submitted a paper to the Astronomical Journal called “The size, density, and formation of the Orcus-Vanth system in the Kuiper belt.”

This paper, I will admit, is less accessible than the paper about fog on Titan, yet, still, would you give it a read? It’s been posted online for a week and one reader already pointed out a rather stupid math error (thanks Alan Martin) of the sort that creeps into papers when you work on them one hour a week for 3 months (the error is still there, until we fix it in the next round of reviews, so feel free to go track it down and marvel at how stupid I sometimes can be).

Normally I would spend a few pages here telling you what the paper is about but, conveniently, I did that last spring, when we were searching for an appropriate name for the moon of Orcus. Go back and reread the post about coming up with names for the moon of Orcus, where I talk about the strange characteristics of what we now call Vanth. And, with a bit of continued Lilah napping over the weeks to come, stay tuned for thoughts about searching for the real Planet X, why I hate the 5 dwarf planets, and strategies for Lilah-weekend-nap-inducement.

And look! Lilah is done with her nap, and ready to start in on last night’s candy. Back to the sugar frenzy. (and with that, Lilah was awake, and we were off, and now it is a month later and Lilah is settled into a post-Thanksgiving nap and I finally have a spare moment to finish and post. Classes end next week for the year, so I look forward to a bit more time for reflection soon. Stay tuned.)

P.S. on the problem with science

I should have, of course, provided the two papers in question so you can decide for yourself. I can't quite do that. I can give you the link to my paper, here:

And I can even provide you with a link to their paper:

But it's possible that you can't read theirs. (but wait: read the comments below; people found all of the parts of this article posted online in various locations, so you're in luck!) Why not? Because, even after $1B of taxpayer money going to send Cassini to Titan and get these results, the copyright to the paper is now owned by Nature. And they say you're not allowed to read it unless you subscribe or pay. If you are logged in from an academic institution, you probably will get access from their subscription. But if you're elsewhere you are simply out of luck. Seems a bit crazy, huh?

If you do get the two papers, be sure to check out the supplementary information in the Nature paper: that is where all of the important details (like where there are and are not clouds) lie. At first glance the two papers look more or less like they say there are clouds in the same spots. It helps that the figures are all really really small so details are hard to discern. But when you blow them up and look carefully things just don't match up nearly as well as two papers using exactly the same data should.

The problem with science

Science is a great system. You examine reality, come up with ideas how it might work, test those ideas, keep the good ones, discard the bad ones, and move on. It’s got one big flaw, though, and that is that science is done by scientists, and scientists are people.

I have a whole slew of scientists mad at me this week – and I will admit that I am pretty irritated back – because none of us cool rational analytical scientists can truly separate our emotions and our egos from the reality-based science that we do. In this current dispute, I get to claim the scientific high ground, at least. My scientific paper that just came out this week unarguably demonstrates that their scientific paper has some rather embarrassing errors. But, in the end, I suspect that even with that seemingly unassailable high ground, I lose the war.

The papers in question are both on the mundane side. They both are catalogs of where the Cassini spacecraft has and hasn’t seen clouds on Titan over the past 4 years. Papers like these, though not going to make headlines anywhere, are nonetheless important contributions to understanding what is going on (at least I think so, or I wouldn’t have taken the time to write one!). Without complete and accurate catalogs of things like where there are clouds on Titan, we cannot begin to understand the more profound questions of why there are clouds on Titan and what does this tell us about the hydrological cycle on the moon. These papers don’t try to answer these questions, but they are necessary pieces of the puzzle.

You would think that two papers that examine the same set of pictures from the Cassini spacecraft to map clouds on Titan would come up with the same answers, but they don’t. And therein lies the root of the problem. When the main topic of a paper is where there are and aren’t clouds on Titan and you sometimes say there are clouds when there aren’t and there aren’t clouds when there are, well, then you have a problem. They have a problem, since theirs is the paper that makes the mistakes. So why are they mad at me? I think perhaps I know the answer, and, perhaps I even think they might have some justification. Let me see if I can sort it out with a little of the convoluted history.

I started writing my paper about 18 months ago. A few months later I realized the other team was writing the exact same paper. Rather than write two identical papers, I joined there team and the two papers merged. The problem was that as I worked with their team through the summer, it became clear that their analysis was not very reliable. I spent hours going over pictures in details showing them spots where there were or were not clouds in contradiction to their analysis. Finally I came to the conclusion that their method of finding clouds and thus their overall paper was unsalvageable. I politely withdrew my name from their paper and explained my reasons why in detail to the senior members of the team overseeing the paper. I then invited them to join me in my analysis done in a demonstratively more accurate way. The senior member of the team agreed that it seemed unlikely that their method was going to work and he said they would discuss and get back to me.

I felt pretty good about this. I had saved a team of people who I genuinely liked from writing a paper which would be an embarrassment to them, and I had done it – apparently – without alienating anyone. I remember at the end of the summer being proud of how adeptly I had navigated a potentially thorny field and come out with good science and good colleagues intact. Scientists are usually not so good at this sort of thing, so I was extra pleased.

I never did hear back from them about joining with me, so when I wanted to present the results of the analysis at a conference in December, I contacted the team again and asked them if they would like to be co-authors on my presentation in preparation for writing up the paper. I was told, no, they had decided to do the paper on their own. Oh oh. I though. Maybe things won’t end up so rosy after all.

Their paper came out first, in June of this year, in the prestigious journal Nature of all places (it’s not hard to figure out the reason for the catty comment often heard in the hallways “Just because it’s in Nature doesn’t necessarily mean that it is wrong.”). I was a bit shocked to see it; I think I had really not believed they would go ahead with such a flawed analysis after they had been shown so clearly how flawed it was (and don’t get me started about refereeing at this point). Our paper came out only this week, but, since their paper was already published, one of the referees asked us to compare and comment on their paper. I had avoided reading their paper until then, I will admit, because I didn’t want to bias our own paper by knowing what their conclusions were and because – I will also admit – I was pretty shocked that they had, to my mind, rushed out a paper that they knew to be wrong simply to beat me to publishing something. I hoped that perhaps they had figured out a way to correct their analysis, but when I read their paper and found most of the erroneous cloud detections and non-detections still there, I realized it was simply the same paper as before, known flaws and all.

So what did I do? In my paper I wrote one of the most direct statements you will ever read that someone else’s paper contains errors. Often things like that are said in couched terms to soften the blow, but, feeling like they had published something that they knew to be wrong, I felt a more direct statement in order.

And now they’re mad.

Reading all of that I certainly hope you come to the conclusion that I am 100% right and they are 100% wrong. You’re supposed to come to that conclusion because I wrote the whole thing from my own biased perspective. And I have my emotions and my ego in there. And I feel wronged.

I’m going to try an experiment from their point of view and see if I can see where I went wrong and irritated them.

Last summer they kindly invited me to be part of their paper, and they shared their non-publicly released data with me (though neither analysis made use of it). They fixed many of the errors that I identified that summer and honestly believed the paper was now good enough. They knew that the analysis wasn’t perfect, but felt like they had invested significant resources in the analysis and that the overall conclusions were correct. So they submitted the paper, and it got accepted in Nature, and they were pretty proud of the effort. Then, out of the blue, my paper is published that says in unusually direct words that their paper is not to be trusted.

Here are some reactions I can guess that they might have had:

(1) Mike Brown’s complaints about are paper are simply sour grapes because our paper came out first and in a more prestigious journal. He is trying to attack our paper so that his paper, which lost the race, somehow seems relevant.

(2) Mike Brown is a nit picker. If you look carefully you will find that while the details of the cloud maps are different between the two papers, the overall conclusions are largely the same. In the end, the conclusions matter, not the details like this.

(3) Mike Brown is a betrayer. He learned about our analysis last summer and then tried to use what he learned against us.

(4) Mike Brown is an impolitic ass, and even if he had concerns about the paper he aired them in an unkind way and now we detest him.

And now I must in the end admit that one of those is actually true. I plead guilty to (4). (1) and (3) are factually incorrect. (2) is bad science (yes: the details matter, not just the conclusions). But (4)? Yeah. OK. Probably. That’s the problem with science. All of those scientists. And few scientists are renowned for their social skills. Even me.

So there are some things that we can all agree with, and some things that we might disagree with. Reality admits little room for differences of opinion. Interpretation of reality, though, is always more subjective.

Everyone should agree: The paper that was published in Nature this June is at times incorrect about where there are and are not clouds. This is simply reality and not open to much discussion (which doesn’t mean there won’t be much discussion).

In my opinion: These errors are fatal for a paper purporting to be about where there are and are not clouds. In their opinion: These errors are not significant and don’t affect the conclusion of the paper. In my opinion my opinion is correct, but I am sure that in their opinion their opinion is correct. Unlikely we’ll come to a conclusion on this one, as this is not about reality, but about interpretation of reality. No analysis is 100% correct and everyone has their own opinion about when an analysis crosses the threshold from mostly correct to fatally incorrect. We have differences of opinions on where this threshold sits, obviously.

In their opinion: The statements in my paper discussing the problems with their paper are disproportionately harsh. In my opinion: The statements in my paper discussing the problems with their paper are harsh, but proportionate to the flaws in the paper. But I will admit that this is the part I am the most uncomfortable with. The statements in my paper are harsh. Maybe too harsh. Did I let too much emotion and pride come in to play as I wrote them? Probably. But as I wrote those statements I was fairly appalled at what seemed to me a lack of concern with reality on the part of their paper. Everyone makes mistakes in scientific papers. Sometimes even big ones. But I had never come across a paper where the mistakes were pointed out before the paper was submitted for publication and the authors had not fixed them. Again, though, my opinion is colored by the fact that I find their analysis fatally flawed. Their desire to go ahead is colored by the fact that they find their analysis good enough.

In their opinion: Mike Brown is a detestable ass. In my opinion: They are shooting the messenger for delivering a message that they already knew. But perhaps both opinions are correct.

Sadly, for me at least, I tried really really really hard to make this work. And to me, “make this work” meant make sure that any papers published which described clouds on Titan were factually correct while at the same time not alienating my colleagues. I failed at both.

So I think we end with this:

The other team will probably always think I crossed a line by writing so harshly of their paper. I will probably always think that they crossed a line by publishing a paper they knew to have factual errors.

Who is right? Probably both. I suspect they let their egos and emotions allow them to care more about publishing a paper in Nature than whether or not that paper was correct. I suspect my ego and emotions caused me to write more harshly than I needed to. That’s the problem with science. It’s done by scientists. Scientists have all of those egos and emotions just like everyone else and no one has figured out a way to leave them at the door when you walk in your lab or your telescope or wherever you sit down to write papers.

In the end though, the only losers in this process are the scientists themselves. While all of us are sitting around feeling wronged, reality marches on. If you would like to know where clouds are or are not you can go read an accurate account. But that’s probably the last paper you will read from me in this field, for I am bowing out. The study of Titan was always just my hobby. A hobby that causes this much anguish is not a very good hobby. Time for a new one. I’ll miss Titan and trying to finally figure out what is going on with all of those clouds, but there are many other interesting things out there in the universe. Time to start exploring once again.

Fog! Titan! Titan Fog! (and a peer review experiment)

Look! Titan has fog at the south pole! All of those bright sparkly reddish white patches are fog banks hanging out at the surface in Titan's late southern summer.

I first realized this a year ago, but it took me until now to finally have the time to be able to put all of the pieces together into a scientific paper that is convincing enough that I can now go up to any person in the street and say: Titan has fog at the south pole!

I will admit that the average person in the street is likely to say hmph. Or yawn. Or ask where Titan is. So let me tell you why finding fog at the south pole of Titan has been the scientific highlight of my summer.

Titan is the only place in the solar system other than the earth that appears to have large quantities of liquid sitting on the surface. At both the north and south poles we see large lakes of something dark. Oddly, though, we don’t actually know what that dark stuff is. At least some of it must certainly be ethane (that’s C2H6, for all of you who have forgotten your high school chemistry). Ethane slowly drips out of the sky on Titan, sort of like soot after a fire, only liquid soot in this case. Over geological time, big ponds of ethane could accumulate into the things that look like lakes on Titan. Odd as they sound, big lakes of liquid ethane are, at least to me, the least interesting possibility. They are the least interesting because ethane is a one way street. Once the liquid ethane is on the ground, it can’t evaporate and is there pretty much forever, unless it somehow sinks into the interior.

Why does all of that ethane drip out of the sky? Because sunlight breaks down methane (CH4) to form ethane much the same way it breaks down car exhaust fumes to form smog in big cities. There’s plenty of methane in the atmosphere, so the supply of ethane is near endless. The dripping will not end soon.

But the methane is where all of the potential action is. Methane is to Titan what water is to the earth. It’s a common component in the atmosphere and, at the temperature of Titan, it can exist in solid, liquid, or gas form. Like water on the earth, it forms clouds in the sky. Like water on the earth, it probably even forms rain. But what we don’t know is whether or not that rain makes it to the surface and pools into ponds or streams or lakes which then evaporate back into the atmosphere to start the cycle over again. In short, we don’t know if Titan has an active methane atmosphere-surface hydrological cycle analogous to the water atmosphere-surface hydrological cycle on the earth.

Until now.

Because there is fog.

Fog – or clouds – or dew – or condensation in general – can form whenever air reaches about 100% humidity. There are two ways to get there. The first is obvious: add water (on Earth) or methane (on Titan) to the surrounding air. The second is much more common: make the air colder so it can hold less water and all of that excess needs to condense. This process is what makes your ice cold glass of water get condensation on the outside; the air gets too cold to hold the water that is in it, and it condenses on the side of your glass.

Terrestrial fog commonly forms from this process. That fog that you often see at sunrise hugging the ground is caused by ground-level air cooling overnight and suddenly finding itself unable to hang on to all its water. As the sun rises and the air heats, the fog goes away. You can also get fog around here when warm wet air passes over cold ground; the air cools, the water condenses. And, of course, there is mountain fog that is causes by air being pushed up a mountain side, where it cools and – you get the pictures – can no longer hold on to all of its water so it condenses.

Interestingly, none of this works on Titan.

It’s really really hard to make Titan air colder fast. If you were to turn the sun totally off, Titan’s atmosphere would still take something like 100 years to cool down. And even the coldest parts of the surface are much too warm to ever cause fog to condense.

What about mountain fog? A Titanian mountain would have to be about ~15,000 feet high before the air would be cold enough to condense. But Titan’s crust, made mostly of ice, can’t support mountains more than about 3000 feet high.

We’re left with that first process: add humidty.

On Titan, as on earth, the only way to add humidity is to evaporate liquid. On Titan this means liquid methane.

Liquid methane! There it is!

Evaporating methane means it must have rained. Rain means streams and pools and erosion and geology. Fog means that Titan has a currently active methane hydrological cycle doing who knows what on Titan.

But there’s one more twist. Even evaporating liquid methane on Titan is not sufficient to make fog, because if you ever made ground-level air 100% humid the first thing it would do after turning into fog would be to rise up like a massive cumulous cloud. There’s only one way to make the fog stick around on the ground for any amount of time, and that is to both add humidty and cool the air just a little. And the way to cool the air just a little is to have it in contact with something cold: like a pool of evaporating liquid methane!

Only final fun part of the story. The fog doesn’t appear to prefer hanging around the one big south polar lake or even around the other dark areas that people think might be lakes. It looks like it might be more or less everywhere at the south pole. My guess is that the southern summer polar rainy season that we have witnessed over the past few years has deposited small pools of liquid methane all over the pole. It’s slowly evaporating back into the atmosphere where it will eventually drift to the northern pole where, I think, we can expect another stormy summer season. Stay tuned. Northern summer solstice is in 2016.

Our paper describing these results (written by me, Alex Smith and Clare Chen, two Caltech undergraduate students, and Mate Ádámkovics, a colleague at UC Berkeley) was recently submitted to the Astrophysical Journal Letters. The paper will shortly go out for peer review, which is an integral part of the scientific process where the paper is vetted by experts. Peer review, as implemented in the current world of over-stressed astronomers, has some serious flaws, though. One problem is that the peer review is performed by one person! Sometimes that one person is thoughtful and insightful and provides excellent insight and commentary. Sometimes that one person misses or misunderstands crucial points. It is rare, though, that any one person can be a broad enough expert in all of the topics in a scientific paper to provide adequate review of the whole thing. Plus people are busy.

What is the solution? I don’t know. There has been much talk recently about all of this, and even some interesting experiments done by scientific journals. I thought I would try an experiment of my own here. It goes like this: feel free to provide a review of my paper! I know this is not for everyone. Send it directly to me or comment here. I will take serious comments as seriously as those of the official reviewer and will incorporate changes into the final version of the paper before it is published.

What kinds of things would I look at closely if I were a reviewer of this paper? Probably things like: is the claim of discovery of something fog-like convincingly made? Is the fog-like feature really at the surface rather than simply a cloud? Is our argument of how fog must form convincing? Is it correct? These were, at least, the things I thought hardest about as I was writing the paper. Perhaps you will find more!

The long road to a Titan storm

Look in your newspaper this Saturday, and you may see a paragraph about Saturn’s moon Titan and a giant storm that moved across the surface last May and what that means. With luck they’ll even print it with a tiny little picture of Titan to catch your eye. Your response, if you have one, will likely be “huh.” It’s OK. I’m not offended. It’s hard to distill the richness of a full scientific paper into a paragraph. And it’s even harder, still, to distill the richness of a decade of scientific inquiry into a short scientific paper. But if you’re curious about what that little paragraph means, and how it came to be in your newspaper, and what we’ve been doing for the past decade, read on. It’s a long story, but that’s somewhat of the point.

I became interested in Titan ten years ago, almost as a matter of convenience. It was an excellent solar system target for the then-new technique of Adaptive Optics, which attempts to undo some of the effects of the smearing of starlight caused by Earth’s atmosphere. Titan was a great target because it is just small enough to be completely smeared by the atmosphere, but big enough that, if you could unsmear it, you would still have a nice view. Just as importantly, no one had ever had a nice view of the surface of Titan before because the satellite it covered in a thick layer of smog which mostly doesn’t let light penetrate to the surface. When the Voyager spacecrafts flew by, they took pictures of Titan which look like a big orange billiard ball. I should have said, though, that visible light doesn’t penetrate to the surface. On the earth, red light penetrates smog better than blue light (hence the nice red sunsets on a smoggy day in Los Angeles). The same happens on Titan. Red penetrates better than blue, but infrared penetrates better still. In fact, if you go far enough into the infrared, you can take a picture of Titan and almost not notice any smog there at all. Conveniently, the new technique of Adaptive Optics works best in the infrared. Hence Titan became a natural target to try out the new techniques on. Antonin Bouchez, then a relatively new graduate student at Caltech, signed on to do this project as part of his Ph.D. thesis.

Our first goals were to obtain maps of the then-almost-totally-unknown surface of Titan. And what a strange looking surface it turned out to be! We speculated endlessly about what all of those dark and bright spots on the surface might be (for the most part it is fair to say that we – and everyone else – had no idea whatsoever until we got better images from Cassini a few years later). And then, in late 2001, we found a cloud sitting at the south pole of Titan.

A cloud!

It doesn’t sound like such a big deal, except that it had long been predicted that Titan was incapable of having clouds. Occasionally there was speculation that clouds of methane might be present, but that, if so, they would be tightly confined to the equator. And yet there it indisputably was: a cloud at the south pole.

Antonin and I were so astounded by this that we put Sarah Horst, then an undergraduate at Caltech, at work looking through a tiny 14-inch telescope on the roof of the astronomy building at Caltech. We had developed some special telescope filters which would – we hoped – be capable of penetrating the haze deck and seeing if Titan got a little brighter due to a cloud or two. We wouldn’t be able to tell anything else, but that would be enough to go back to the giant Keck telescope and say “Look now! There will be a cloud!”

It worked. Just a month after our first cloud detection Sarah saw something that looked just like what we expected a cloud to look like. We called people at the Keck telescope and begged them to snap a picture, and there it was. A much bigger splotch, still near the south pole.

I’m an astronomer, not a meteorologist. I had to spend six months learning about how clouds worked, trying to understand precisely why people thought they wouldn’t occur on Titan, and figuring out what was wrong. On a long summertime flight across the country where we continuously skirted afternoon thunderstorms, it all came together: no one had ever previously bothered to consider the effect of Titan’s surface heating. Like Arizona on a summer afternoon, Titan’s surface can heat up and eventually drive convective clouds over it. On Titan, though, it doesn’t happen in the afternoon. It happens in the summertime, when the south pole spends something like 10 years in continuous sunlight.

It was a compelling story, and, I think true. But, even better, it made some fairly clear predictions. The clouds were at the south pole when we discovered them only because it was very close to southern summer solstice. Titan (and Saturn) takes 30 years to go around the sun, so its seasons are quite long. But if you had the patience to watch, you should see the clouds move from the south pole to the north pole over the next 15 years before coming back 15 years later.

Antonin eventually got his Ph.D. and moved on to take a job working with the technical team continuing the development of Adaptive Optics at the Keck Observatory. It was the perfect place to be. Whenever there was a spare moment or two at the telescope, he would swing it over towards Titan and snap a picture. The clouds were nonstop. Sometimes there were just a few tiny specks, but occasionally there would be a huge outburst. It was a thrilling show to watch.

Emily Schaller entered graduate school at Caltech at just about that time, and she decided to do her thesis on watching and understanding these developing clouds on Titan. The first year was exciting, indeed. She saw a monster cloud system cover the south pole of Titan and remain for more than a month (disappearing just as one of the first close Cassini flybys went in to take pictures; Cassini saw a few wispy little clouds but missed almost all of the action). Henry Roe, a recently graduated Ph.D. from the University of California at Berkeley who had been using the Adaptive Optics on the Gemini telescope to study Titan, moved down to Caltech to work with us, and the odd discoveries about the clouds poured in. They appeared to finally move north from the pole; they appeared tied to one spot at 40 degrees south latitude for a while; they untied themselves; bright clouds in one spot seemed to foretell bright clouds in another. It was clear that we were amateurs here. We enlisted the help of Tapio Schneider, a professor of environmental engineering at Caltech and one of the world’s experts on atmospheric circulations, to help us make sense of what was going on. Things were finally falling into place.

In one final piece of exceedingly clever astronomy, Emily Schaller replaced our clunky nightly observations with a 14-inch Celestron, originally begun by Sarah Horst, with a sleek set of nightly observations from NASA’s Infrared Telescope Facility on top of Mauna Kea. The IRTF would take a quick spectrum of Titan every night possible, and Emily could quickly look at the rainbow of infrared light to tell precisely how many clouds were there. And when they looked good, she could tell Henry Roe, who would get the Gemini telescope to examine them.

And then the clouds stopped.

For years and years Emily would look at her data in the morning and walk across the hall to my office to mournfully say “no clouds again last night.” Seeing no clouds is scientifically interesting, and she dutifully wrote papers and indeed an entire chapter of her Ph.D. thesis demonstrating and trying to explain this years-long lack of clouds. But, really, I understood. Explaining a lack of something is not nearly as satisfying as actually getting to see something happen. As her advisor, I would have been happy to fly to Titan to perform a little cloud-seeding, but no one had yet figured out exactly what chemicals or incantations might do the trick.

On April 14^th last year, Emily walked across the Caltech campus to finally turn in her thesis. Then she did what she did most mornings: she walked to her office, downloaded the data from the night before, and checked to see if Titan had clouds. That morning, I suspect, she came close to falling out of her chair. She was likely exhausted from those final stretches of thesis writing, and I am sure that the first time she plotted her data she did what I always do when I see something astounding: she assumed she had made a mistake. She probably re-downloaded the data, double-checked the coordinates, and shook herself a little more awake. But it was no mistake. Titan suddenly had the largest cloud system seen in years. She likes to say it was Titan throwing a graduation party for her. But I know better: I think Titan likes to hide its secrets as long as possible, and knew it was finally safe to let go.

The scientific paper that Emily wrote along with Henry, Tapio, and I that appears in Nature describes the big cloud outburst and its scientific implications. And the implications are pretty fascinating. This big cloud outburst – the biggest ever seen – began in the tropics of Titan, where it has been speculated that clouds, if they ever form, should be weak wispy things. The tropics are where, of course, the Huygens spacecraft that landed on Titan took dramatic images of things that look like stream beds and shorelines and carved channels. How could those be at the equator if there are never clouds and never rain? People asked.

This discovery doesn’t actually answer that question, because we don’t know why there was a huge outburst of clouds in the tropics of Titan. But it does perhaps answer that lingering question: How could those be at the equator if there is never rain? Because there is rain.

Now, however, I am going to allow myself to speculate a bit more than we were comfortable speculating in the scientific paper. I am going to ask: Why? Why were there clouds in the tropics? Why did they appear suddenly at one spot? What is going on?

What I think is going on (again, I warn you, rampant speculation follows…) is that Titan occasionally burps methane, and I think Emily found one of the burps. For many years scientists have wondered where all of the methane in Titan’s atmosphere comes from, and, I think, here is the answer. The surface occasionally releases methane. Call it what you want. Methane geysers? Cryovolcanoe? Titanian cows? Whatever happens, the methane gets injected into the atmosphere and, at that location, instantly forms a huge methane cloud. Massive rainout ensues downwind. The stream channels, the shorelines, and everything else in the otherwise desert-seeming regions are carved in massive storms.

Evidence? Evidence? Where’s the evidence? You scream. Fair enough. I am giving you a snapshot of how science is done, and, at this point, this is the hypothesis stage. Or hunch. Or speculation. This hunch is the type that then guides what we go off to try to observe next. What will we see? Will the spot Emily found burp again? That would be pretty striking confirmation. Will other spots blow? (I should mention that we do indeed think we saw a different spot burp a few years ago).

At this point we have observed Titan well for about 7 years, from the winter southern solstice until the northern spring equinox, which actually just occurred last week, the terrestrial equivalent of late December to late March. What will the rest of the year reveal? We’re still watching, waiting. Maybe in 23 years, when we’ve finally seen an entire season, we’ll call it a day.

The Joys of Rejection and Lake-effect clouds on Titan

Remember my new paper that describes my interesting discoveries about Titan (see Your Saturday Newspaper)? submitted it to Science magazine a few weeks ago in the hopes that it will be published and some day make it to your Saturday newspaper. But it won't. It has been rejected.

It was a kind rejection. They didn't say "we think you're paper is wrong." Just, "we don't find it of general enough interest to publish in our journal."

Rejection is always hard. My first response was generic sputtering “wha.. wha… what?” and then disbelief “this can’t be!” and anger and dismissal “those idiots don’t even know what they are missing.” This sequence lasted about 7 seconds, and then I got over it. After about 1 minute I became excited.

Why be excited about rejection from Science? Along with the publicity benefits of publishing a paper in somewhere like Science comes the hard part. You agree not to publicize or discuss the paper before the publish it. This process can take 6 months or longer.

But having been rejected from Science, I quickly turned around and submitted the paper to a more specialized journal -- Geophysical Research Letters (aka GRL) -- which has no such restrictions, and then I went a step further and submitted it to an on-line electronic archive ( which means you can go read it right now! http://lanl.arxiv.org/abs/0809.1841 ).

Scientists these days are increasingly speeding up the slow process of formal publication with an informal process of web publication. Such web publication has good and bad aspects to it. Good: instant. Bad: unreviewed.

Anything that is published in a major journal has had one or two experts read it closely and suggest changes. My paper on Titan is currently undergoing this process at GRL, and, when the reviewers are done, I will modify and respond. But my paper is on the electronic archive for everyone to see before that even happens.

Posting a paper on-line before it has been reviewed can lead to great embarrassment. What if the paper has fundamental flaws and needs to be withdrawn or rejected? What if the referees point out places where major changes need to take part? All of this is certainly possible, and should make any on-line submitted wary. But, for me, the benefits outweigh the risks. I am sufficiently confident in the accuracy of what I did that I am not worried about any of these major problems. While there is no doubt that the reviewers will suggest some improvements, I don’t believe the overall conclusions of the paper will change significantly. And I think the conclusions are sufficiently interesting that I relish the idea that people will begin to read the paper and think about the results now, rather than 6 months from now. So I submitted.

And now, even better, I can talk about the discovery of lake-effect clouds on Titan.

Earlier this summer, while looking through NASA’s on-line archives of images of Saturn’s satellite Titan taken from the Cassini mission, I began to notice a recurring pattern up near the north pole of the satellite. The north pole of Titan has been in the darkness throughout a long long winter (a full year on Titan takes 30 years; winter is almost a decade) and is just now emerging into some spring time daylight. As it began to emerge, I noticed what appeared to be tiny little clouds popping up and disappearing right over the pole.

Titan is in some ways bizarre and exotic yet in some ways very earth-like. Both earth and Titan have mostly-nitrogen atmospheres; on both the surface pressure is about the same (the big difference on Titan: it lacks that minor contaminant – oxygen – that makes the earth a more interesting place….).

Titan and earth are the only bodies in the solar system known to have large expanses of liquid at the surface. On Titan, though, the temperature is so low that water is frozen solid. The lakes of Titan are made, instead, of methane and ethane. If you could figure out a way to get a pipeline there, Titan’s lakes could supply all of our needed natural gas for years to come.

On earth the liquid water is globally distributed. On Titan it appears that the liquid methane and ethane is confined to the poles.

Finally, Titan and earth both have clouds in its atmosphere, and these clouds are made from the dominant liquid on the surface. On earth: water. On Titan: methane.

Now, back to the little clouds I had seen popping up at the north pole during Titan’s early spring.

These clouds surprised me; they appear to be cumulous clouds – like large thunder heads. On the earth we only get such clouds in hot, humid places. Arizona in August. Year-round in the tropics. Temperate latitudes during summer storms. How could such clouds possibly be up at the north pole just as winter is waning?

It occurred to me that we do get winter cumulus-type clouds on the earth in at least one case: lake-effect clouds and storms. Lake-effect storms on the earth are those winter storms that blow across the Great Lakes, pick up moisture, and then proceed to dump many many feet of snow on places like Buffalo, New York.

The effect occurs in many other places around the world. Or, I should say, they same effect occurs in many other places around the solar system. I believe this process is precisely what is causing the sporadic clouds at the north pole of Titan.

Like everything else, Titan and earth have similarities and differences in their lake-effect clouds, too. On the earth, the formation of these clouds is greatly aided by the fact that deep lakes stay relative warm over the winter. So as cold air passes over these lakes the air both picks up humidity and a little heat. This heat causes the air to rise (like a hot air balloon) which, in turn, causes those cumuli and the subsequent snow.

On Titan, a decade of polar winter means that none of the lakes retain any heat, so passing air only picks up humidity (methane humidity, in this case). Something else needs to help push the air higher to cause those cumuli. In the paper, we speculate that there might be mountains at the north pole that help, but really that is just a wild guess.

Cold lakes won’t evaporate, so these clouds have only started to become active in the last few years as sunlight has started to every-so-slightly heat the lakes. Every time the lakes warm up just a bit, a huge dollop of evaporation occurs, which re-cools the lake, and we see a cumulus cloud pop up. The lake then has to wait for some more sunlight before it happens again.

If our general story is correct – and I think it is – then as spring and then summer approaches at the north pole, the sunlight will increase dramatically, and the lake-effect clouds will start to go crazy. And we’ll be watching. The Cassini spacecraft is slated to continue flying past and taking pictures of Titan for several more years. And we might find more exciting things.

And what will we do when we find exciting things? Well, in the end I will probably never learn my lesson. We’ll submit them to Science. Or we’ll submit them to Nature. And then we will have to wait for months to talk about them. And maybe they will get a paragraph in your Saturday paper. But, if we – and you – are lucky, we will instead be rejected, we’ll post to a freely available on-line archive, and everyone can hear early about the latest happenings on this bizarre satellite.

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