Tuesday, February 06, 2007

Meanwhile, Back on Titan

The world is my country, science is my religion. ~ Christiaan Huygens

Want an idea how time just flies by? It's been two years since the Huygens probe landed on Titan.

Cassini-Huygens, as it was known at the time, arrived at Saturn after about a seven-year trip. Going to Saturn is daring enough, given all those ring-plane crossings, but going there to eject a probe to land on one of its moons is downright extravagant. But, right on schedule, Cassini, the size of a school bus, sent it's little partner Huygens, the size of a washing machine, hurtling toward Titan.

The result was an immense success, although at the time, some of the most valuable atmospheric data appeared to be lost due to a glitch in the antenna system. But, in one of those little miracles that occurs in the exploration of space, a bunch of radio dishes that weren't even supposed to be involved were listening. Because of the feeble signal from Huygens, even though they were listening, there was no reason to suspect that they would get any meaningful data. Yet, they did. No one scope got all of it all, but thanks to some very clever work, the Huygens team was able to piece the bulk of the data back together rescuing the seemingly lost information.

It's been that kind of mission.

Now, one of the standard quotes out of scientists when a satellite, probe, or rover goes somewhere is that it will take years to understand all the data coming back. And, too often, that's been the last the average person has ever heard of it. Primarily that's because the makeup of, say, Martian dirt isn't all that newsworthy to the mainstream media. So, unless you subscribed to astronomical journals or exobiology seminars, you probably didn't get to hear much about what was found.

The Internet has changed that. Thanks to numerous web sites that follow such activities, and with the judicious use of news aggregators, one can indeed find that scientists are, in fact, still learning things from data gathered years ago. Huygens is no exception.

The thing most people think of when they think of the Huygens landing on Titan are the spectacular photos of the moon's terrain. It was so familiar looking, with all the signs of liquid having flowed down to a plain that initially looked like a sea. There was a bit of disappointment when it turned out that there was no methane ocean to land in, but, as is often the case, the lack of one characteristic simply opens up more questions about what we did see.

It certainly hasn't hurt that Cassini itself has sent back reams of data about Titan. Coupling this information with what Huygens recorded is allowing the Cassini-Huygens team to build up a tentative picture of a fascinating place.

We hoped for an ocean; we didn't get one, but what we've seen is a much more varied place than we expected. It's amazing, really, that we keep being surprised. After two Voyager missions and the Galileo mission, we should have come to realize that we should expect these extraterrestrial places to be more interesting than expected. Titan is proving to be no exception.

Despite the fact that we haven't found a methane ocean, it's clear that liquid methane has played and probably still is playing a major role in Titan's life, just as water does here on Earth. For example, the pebbles that Huygens showed us, combined with the impact forces registered, imply that the probe landed in an “outwash”, a place where liquid (I keep wanting to say “water”, but that doesn't work at Titan's temperatures) flowed as, say, a stream might flow across a plain.

So where is the methane? Well, Cassini's radar has imaged what appear to be methane lakes. But methane would evaporate over time, so how do lakes get replenished? It must rain methane. One open question, then, is does it come down in drenching downpours or a sort of steady drizzle? That question may be answered by a new discovery by Cassini.

In a January pass, Cassini viewed a massive cloud, as big as the United States, over the northern polar region. This cloud has just become visible as Titan moves out its “winter” tilt so that light falls on the area. This cloud could be a massive methane rain storm, dumping lake-filling quantities of the liquid back to the surface.

Another Huygens finding shows that Titan is almost surely still geologically active, based on the detection of argon isotopes. This activity is probably in the form of “cryo-volcanos”, eruptions of water ice and methane, a theory supported by apparent “lava” flows, although this “lava” would be a sort of slush, not molten rock.

The fun is really just starting when it comes to discoveries about Titan. Cassini is going to perform 22 more flybys of the moon over the next 18 months, and, if the mission is extended (which is a definite possibility), there could be more. Every flyby has revealed more details that, taken with Huygens' data, fills in a few more pieces of the Titan puzzle.

Of course, it's a very large puzzle. But that's the kind scientists love.

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