The many moods of Titan

Feb 23, 2012
This series of false-color images obtained by NASA's Cassini spacecraft shows the dissolving cloud cover over the north pole of Saturn's moon Titan. Image credit: NASA/JPL-Caltech/University of Arizona/CNRS/LPGNantes

(PhysOrg.com) -- A set of recent papers, many of which draw on data from NASA's Cassini spacecraft, reveal new details in the emerging picture of how Saturn's moon Titan shifts with the seasons and even throughout the day. The papers, published in the journal Planetary and Space Science in a special issue titled "Titan through Time", show how this largest moon of Saturn is a cousin - though a very peculiar cousin - of Earth.

"As a whole, these papers give us some new pieces in the jigsaw puzzle that is ," said Conor Nixon, a Cassini team scientist at the NASA Goddard Space Flight Center, Greenbelt, Md., who co-edited the special issue with Ralph Lorenz, a Cassini team scientist based at the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. "They show us in detail how Titan's atmosphere and surface behave like Earth's - with clouds, rainfall, and lakes. They show us that the seasons change, too, on Titan, although in unexpected ways."

A paper led by Stephane Le Mouelic, a Cassini team associate at the French National Center for Scientific Research (CNRS) at the University of Nantes, highlights the kind of seasonal changes that occur at Titan with a set of the best looks yet at the vast north polar cloud.

A newly published selection of images - made from data collected by Cassini's visual and over five years - shows how the cloud thinned out and retreated as winter turned to spring in the .

This series of images obtained by NASA's Cassini spacecraft shows several views of the north polar cloud covering Saturn's moon Titan. Image credit: NASA/JPL-Caltech/University of Arizona/CNRS/LPGNantes/SSI

Cassini first detected the cloud, which scientists think is composed of ethane, shortly after its arrival in the Saturn system in 2004. The first really good opportunity for the spectrometer to observe the half-lit north pole occurred on December 2006. At that time, the cloud appeared to cover the north pole completely down to about 55 degrees north latitude.  But in the 2009 images, the cloud cover had so many gaps it unveiled to Cassini's view the hydrocarbon sea known as Kraken Mare and surrounding lakes.

"Snapshot by snapshot, these images give Cassini scientists concrete evidence that Titan's atmosphere changes with the seasons," said Le Mouelic. "We can't wait to see more of the surface, in particular in the northern land of lakes and seas."

This artist's concept shows a possible model of Titan's internal structure that incorporates data from NASA's Cassini spacecraft. In this model, Titan is fully differentiated, which means the denser core of the moon has separated from its outer parts. Image credit: A. D. Fortes/UCL/STFC

In data gathered by Cassini's composite infrared mapping spectrometer to analyze temperatures on Titan's surface, not only did scientists see seasonal change on Titan, but they also saw day-to-night surface temperature changes for the first time. The paper, led by Valeria Cottini, a Cassini associate based at Goddard, used data collected at a wavelength that penetrated through Titan's thick haze to see the moon's surface. Like Earth, the surface temperature of Titan, which is usually in the chilly mid-90 kelvins (around minus 288 degrees Fahrenheit), was significantly warmer in the late afternoon than around dawn.

"While the temperature difference - 1.5 kelvins - is smaller than what we're used to on Earth, the finding still shows that Titan's surface behaves in ways familiar to us earthlings," Cottini said. "We now see how the long Titan day (about 16 Earth days) reveals itself through the clouds."

A third paper by Dominic Fortes, an outside researcher based at University College London, England, addresses the long-standing mystery of the structure of Titan's interior and its relationship to the strikingly Earth-like range of geologic features seen on the surface. Fortes constructed an array of models of Titan's interior and compared these with newly acquired data from Cassini's radio science experiment.

The work shows the moon's interior is partly or possibly even fully differentiated. This means that the core is denser than outer parts of the moon, although less dense than expected. This may be because the core still contains a large amount of ice or because the rocks have reacted with water to form low-density minerals.

Earth and other terrestrial planets are fully differentiated and have a dense iron core. Fortes' model, however, rules out a metallic core inside Titan and agrees with Cassini magnetometer data that suggests a relatively cool and wet rocky interior. The new model also highlights the difficulty in explaining the presence of important gases in Titan's atmosphere, such as methane and argon-40, since they do not appear to be able to escape from the core.

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kevinrtrs
1.7 / 5 (11) Feb 23, 2012
The new model also highlights the difficulty in explaining the presence of important gases in Titan's atmosphere, such as methane and argon-40, since they do not appear to be able to escape from the core.

Just to clarify for those not in the know:
The difficulty arises from the fact that after the assumed 4.5 billion years of existence in the solar system, there is still methane left in the atmostphere. If there were/was a way for the methane to escape the core, it would have been easy to explain that that escape was the source for the current presence of methane. But now there is no such easy explanation to be had because methane doesn't appear to come from the core. This means that another, more damning possibility might have to be considered, namely that perhaps Titan is not 4.5 billion years old. If that is the case then it becomes even more difficult to explain where Titan came from.
Now since that possibility cannot be considered, it therefore is very difficult to explain
LEDman
5 / 5 (5) Feb 23, 2012
Or the possibility that methane is simply being generated by a mechanism that we don't understand.

Why jump to the conclusion that Titan can't be 4.5 billion years old instead of saying hey, there must be a chemical reaction going on that we don't understand.

There is methane (not a lot granted) found in the atmosphere of Mars. Does that mean that Mars isn't 4.5 billion years old?

Wait a minute, the atmosphere of the Earth is loaded with oxygen and that couldn't possibly be escaping from the Earth's core. Given the reactivity of oxygen, the Earth couldn't be more than a few hundred years old and it will all be gone soon and we will be dead.
kevinrtrs
2 / 5 (8) Feb 24, 2012
@LEDMAN, why do YOU want to dismiss the possibility that Titan might be younger than is normally accepted?

Just which chemical reaction is going on that we currently don't understand? Can you begin to name something more concrete?

Do you realize that you are appealing to a completely unknown and unobserved entity whilst dismissing a far more reasonable and totally plausible explanation? This dismissal being made on the basis that the solar system MUST be 4.5 billion years old, no matter how much actual physically recordable evidence is seen to contradict that notion?

Which is more likely at this stage of our knowledge of planetary [and in particular, Titan(ic)] geological chemistry?

Your analogy of oxygen in earth's atmosphere is simply misplaced and invalid and not applicable at all.
Torbjorn_Larsson_OM
5 / 5 (4) Feb 24, 2012
Interesting, if the inner models are true. Then Titan may be an even better candidate for life (in its oceans) than Europe, because they imply minerals can leach out into the water volume for sure.

@ kevinrts:

There is absolutely no "actual physically recordable evidence" that the solar system is anything but 4567.2 /- 0.5 million years old (the latest figure, from "Chronometry of Meteorites and the Formation of the Earth and Moom", Kleine et al), and I note you present none.

Titan may be younger, we now know that there is a large population of nomad planets, potentially outnumbering stars 10^5:1 ("Nomads of the galaxy", Strigari et al). Even if most of those captured would average 10 000 au in distance, some may get closer.

However, Titan is prograde, tidally locked with Saturn, so is most likely an intrinsic moon made up of what didn't become the planet.

LEDman's analogy shows that the state of an atmosphere evolves over time. What "possibility cannot be considered"?
roboferret
4.6 / 5 (8) Feb 24, 2012
Do you realize that you are appealing to a completely unknown and unobserved entity whilst dismissing a far more reasonable and totally plausible explanation?


The irony, it hurts!
aroc91
5 / 5 (1) Feb 25, 2012
Do you realize that you are appealing to a completely unknown and unobserved entity whilst dismissing a far more reasonable and totally plausible explanation?


I've hypothesized in the past that kevin is a creationist parody and this is further evidence. Way too obvious this time, kevin.