The Sirens of Titan

by Michael Tobis     Department: Earth

Last time, I talked about the annual Fall Meeting of the American Geophysical Union,  focusing on the sessions that got the most press. These were presentations about climate change aimed at a broad audience. I tried to stress that these weren't typical of an AGU meeting.

What sorts of topics are covered? Categories include biogeosciences, cryosphere, geodesy, mineral and rock physics, seismology, aeronomy, and "vulcanology, geochemistry and petrology", the last being a single category. Most members of the AGU know a lot about some of the topics covered and very little about some others. I for one cannot even define "petrology", so I won't presume to explain it to you. Just out of curiosity here are a couple of presentations from one of those sessions. "Experimental Constraints on AI Solubility in Model Granitic Fluids at 700 C and 1 GPa" (a computational experiment I hope) by Wohlers and Manning, and "Crystal Size Distributions of Periclase in Contact Metamorphic Marbles as a Record of Fluid Infiltrations" by Mueller et al. Your guess is as good as mine. I expect "contact metamorphic marbles" is a vigorous game involving rolling little glass spheres around, but I am not too sure.

Are these good contributions to science? Do they contribute to active areas of interest in their community? I can't tell. I am confident that Wohlers or Mueller could make a case linking their efforts to things that matter.

It's easy to convince yourself that none of this matters. This is the "ivory tower" critique, or the way "acadeic" is used as a putdown. I recall telling an illiterate refugee that my job involved studying clouds. He laughed loud and long about the strangeness of the West, where a man could be paid to stare at the sky all day.

I understood his way of thinking far better than he understood mine. We are all illiterate about great swaths of science. It is hard to know what is worthy of study and what isn't. It's hard enough for someone in the know about somthing to remember how he or she thought before that something was known, but it's practically impossible for the person who doesn't know it to understand the motives of the person who does.

Consider this. A man for whom I have the greatest regard, Dr. Ray Pierrehumbert of the University of Chicago, has long been fascinated by the climates of other planets, including their ancient climates. I find this amusing, in that the climate of Mars a billion years ago is a topic of study where one can operate in blissful confidence that none of one's theories will ever be tested by the slightest amount of data. Nevertheless, I personally know of Ray's intellectual rigor and intellectual honesty. I am confident that his pursuits in this direction are likely to lead somewhere.

Recently, Ray and his students, notably Jonathan Mitchell, now of the Institute for Advanced Studies at Princeton University, have been paying a lot of attention to the atmosphere of Titan, the great moon of Saturn. Clouds have been observed on Titan for some time now, and a few mechanisms have been proposed, but Pierrehumbert and Mitchell are confident that the mechanisms of these clouds are essentially similar to the mechanisms that cause clouds on earth. There's just one small difference; the clouds and the ocean that spawns them are made of methane, not water.

There has been some press coverage  and even a slashdot story, none neglecting Ray's Titanic motto that Titan, though its temperature hovers around 270 degrees below zero Fahrenheit, is a "tropical world". None of the press stories, though, manages to capture the nature of Ray's group's fascination with Titan. I had the privilege of watching Ray explain the matter at an AGU talk last week.

It turns out that this second example of multiple phases and clouds in the solar system is of considerable interest. "Dynamicists", a breed of mathematician / meteorologist / geophysicists, can come up with some general theories of how worlds with atmospheres and oceans ought to work. In particular, much of our future depends on how robust the generalization that the relative humidity of the atmosphere is nearly constant is. A theory has emerged to justify this observation, and to take it far outside the realm of observations, and into the greenhouse-gas enhanced world of the imminent future. Can the theory be tested against a broader range of conditions? Well, one test is better than none, and it turns out that properly accounting for various scale changes in going from Earth to Titan places both on a very clear line of correlation that is defined by a myriad of model instances.

So Titan has provided a result that is deeply important to how we understand our own world, even though the data is coming from the orbit of Saturn.  
 
Similarly, whether or not you find it silly, I plan to keep looking up at the clouds, and that's why I'm reluctant to criticize an interest in ancient Mars (which probably, it turns out, had oceans).

There is more to my cloudwatching than I can explain in a hurry. It all hangs together in the most amazing way, all the clouds, real and simulated, water and methane, past and future, if you watch carefully and diligently enough.

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