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A Look Into Titan’s Haze

Voyager’s controllers thought so much of Titan that when Voyager 1 approached Saturn and the choice arose between sending it on to the outer planets or taking a sharp jog off the ecliptic to view the enigmatic moon, they chose the latter. We all know the result: Titan remained as mysterious as ever, its surface shrouded in orange haze. But you can see why they needed that look. Here was a moon that was large enough to be a planet, with a thick atmosphere and all kinds of speculation about what was on its surface. No wonder Titan was the most tempting of targets, and one of huge scientific value.

These days we routinely get Cassini imagery from Titan flybys, and the place has gained definition. I remember once asking Geoffrey Landis, having read his superb 2000 novel Crossing Mars, whether Mars had become more or less an everyday place to him, like Cleveland (he lives there, working at NASA GRC). And it was true: After you study and survey and write novels about a place, it does become tangible, acquiring familiar placenames and recognizable surface features. Titan is becoming like that, with its lakes of liquid methane/ethane, its well studied seasonal change, its steadily building catalog of placenames.

Image: Voyager 1 couldn’t see through Titan’s haze, but after numerous Cassini passes and simulations here on Earth, we’re learning much more about this world’s atmosphere and its implications. Credit: NASA/JPL/Caltech.

And now we’re gaining insights about the chemical processes at work on the distant moon. It turns out that, as we’ve long suspected, the basic ingredients for life are available here, and what’s more, they’re occurring in the outer layers of the atmosphere without the need of a surface. As revealed in simulations carried out in France by a team led by researchers from the University of Arizona, a wide variety of complex organic molecules including amino acids and nucleotide bases can be produced in a simulated Titan atmosphere. Sarah Hörst, who works the university’s Lunar and Planetary Lab, helped to lead the research effort:

“Our team is the first to be able to do this in an atmosphere without liquid water,” says Hörst. “Our results show that it is possible to make very complex molecules in the outer parts of an atmosphere.”

The five nucleotide bases life uses on Earth to make the genetic materials DNA and RNA – cytosine, adenine, thymine, guanine and uracil — all turn up in the simulations, and so do the amino acids glycine and alanine. The work was presented at the Division of Planetary Sciences meeting in Pasadena that has produced so much interesting outer system work this year, including the results on Eris and the work on Neptune’s interactions with the Kuiper Belt that we looked at on Friday. Titan’s haze, we now learn, may be a reservoir of prebiotic molecules, and we have the interesting possibility that such precursors may have fallen to Earth out of its own primordial haze as life began to take hold here.

That smoggy orange ball Voyager I saw is loaded with aerosols laden with organic molecules. Here things get even more interesting, because while Titan’s surface probably lacks the energy needed to break apart atmospheric nitrogen, methane and carbon monoxide, rearranging them into more complex prebiotic molecules, the upper reaches of the atmosphere are exposed to ultraviolet radiation, not to mention charged particles from the Sun that have been deflected by Saturn’s magnetic field. The researchers mixed gases found in Titan’s atmosphere in the lab in Grenoble and simulated the energy hitting the upper atmosphere by using microwaves, causing some of the raw materials to bond together.

Image: A window into Titan’s atmosphere: Energized by microwaves, the gas mix inside the reaction chamber lights up like a pink neon sign. Thousands of complex organic molecules accumulated on the bottom of the chamber during this experiment. (Photo: S. Hörst)

The results from the work were striking. 5,000 different molecular formulae turn up with these simulations as analyzed by a mass spectrometer. Says Hörst:

“We really have no idea how many molecules are in these samples other than it’s a lot. Assuming there are at least three or four structural variations of each, we are talking up to 20,000 molecules that could be in there. So in some way, we are not surprised that we made the nucleotide bases and the amino acids… We never started out saying, ‘we want to make these things,’ it was more like ‘hey, let’s see if they’re there.’ You have all those little pieces flying around in the plasma, and so we would expect them to form all sorts of things.”

Is the same kind of chemistry at work in the atmospheres of planets around other stars? The Titan simulations give the idea continued plausibility, another indication that life may be commonplace in the galaxy or, at least, that the conditions for its formation should not be rare. We’ve come a long way from the iconic Chesley Bonestell images of Titan to today’s hazy landscapes sculpted by liquid ethane/methane and laden with a dense prebiotic soup of an atmosphere. It’s a fascinating world, as we’ve long suspected, and it’s giving us clues about the chemistry that produces biological material and eventually leads to life.

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Comments on this entry are closed.

  • Scott G October 11, 2010, 12:45

    I love the picture of Titan included with this article. It makes a world a billion miles away look so accessible, as if we were descending through its upper atmosphere about to make our first human-piloted landing there. I sure hope we get an aggressive space exploration policy in place so this might become a reality sooner rather than later.

    And the fact that we’re able to reproduce thousands of organic molecules, including the precursors of DNA/RNA, by simulating Titan’s atmosphere almost solidifies in my mind that there’s got to be life out there — and probably even within our own solar system. We just have to muster the will to put a program together to go find it.

    As astrobiologists Carol Stoker and Christopher McKay (of NASA’s Ames Research Center) put it, referring to Mars in the Oct. 1 issue of Science (but applicable here), “it’s time to search for life by searching for life” (Stoker) … “rather than taking more pictures of rocks” (McKay).

  • NS October 11, 2010, 14:38

    There are a number of discussions about possible balloon probes of Titan, but here’s a concrete development:

    http://www.aurora.aero/Communications/Item.aspx?id=apr-245

  • Eniac October 11, 2010, 14:46

    Finding all these organics is very exciting, but they are only one of the necessary ingredients for life. Who knows what else is required. The one “requirement” we know best is liquid water, and there is none of it on Titan. You could have real protein and DNA there, but without water they would be just so much dead, tarry stuff.

    If I had to pick a place for abiogenesis on Titan, I would pick the lakes. No water there, either, but at least you have something liquid, a place for the molecules to diffuse about and interact with each other in complex ways.

  • Tarmen October 11, 2010, 16:16

    And all of these rains and ethanol seas and dunes and streams and seasons and proto organics . All churning away on a moon! Many strange landforms and geologies will have been carved out over the millenia. Seven Wonders of the World!
    That world must possess a weird spooky beauty. Someday to be witnessed from a (nuclear-heated) science base at the edge of Lachus Ontario.

  • NS October 11, 2010, 17:09

    A general review of Titan balloon concepts (pdf):

    http://www.lpl.arizona.edu/~rlorenz/balloonjbis.pdf

  • John Freeman October 11, 2010, 18:55

    I want to know what the other 19, 993 molecules are! A very very complex world.

  • ljk October 12, 2010, 1:15

    It was later learned that Voyager 1 did not flyby Titan in 1980 in complete vain, for the probe’s cameras did faintly detect actual surfaces features.

    See here for the amazing images and details:

    http://www.astro.cornell.edu/~richardson/vgertitan.html

    To quote:

    For many years, the conventional wisdom has been that Voyager 1 was unable to detect the surface of Saturn’s moon Titan during the spacecraft’s November 1980 close flyby, due to the moon’s thick, hazy atmosphere. Recent re-processing of these images has shown that the Vidicon imaging systems onboard Voyager 1 did indeed detect the surface of Titan, although faintly and at low resolution. At left is a ‘classic’ full-color view of Titan’s hazy atmosphere, produced from Voyager 2 images (courtesy SEDS), while at right is a new (as of this work) orange filter (600 nm) view of Titan’s surface albedo features, produced from Voyager 1 images. The finding of Titan’s surface features in these orange filter images from Voyager 1 has positive implications for the Cassini mission, indicating a large range of possible wavelengths over which Cassini’s superior imaging systems may be used to study the cloaked surface of this large moon.

  • Procyan October 12, 2010, 3:50

    Building blocks abound. So do mineral catalysts. But catalysts run equally well in either direction. We need to find a mechanism that somehow protects the nacent polymer, be it protein, nucleic acid or some other, from reverse engineering itself back into building blocks as fast as it forms.

    There are strong arguments for liquid ammoniated water on [in?] Titan. It is conceivable that a 2 phase system exists there that is conducive to polymer formation. For example an aqueous soup of amino acids in contact with clay minerals may start to polymerize. If the growing protein chain is hydrophobic, it may pass through the aqueous/organic boundary and become sequestered into an organic phase that allows it to fold into a stable structure. Once assembled, this 3 dimensional shape would have vastly reduced affinity for the catalyst and survive to function as a progentitor molecule. The next steps to complexity and life seem forgone once this hurdle is passed.

    I predict that we will learn about the origin of life from Titan, but not until we go there and scoop the goop.

  • kzb October 12, 2010, 7:24

    I wonder what it smells like on Titan -like an old organic chemistry lab ?

  • ljk November 9, 2010, 8:56

    The mysteries of Titan

    Thirty years ago this week Voyager 1 made the first close flyby of Titan, Saturn’s largest moon and one of the most intriguing worlds in the solar system. Andrew LePage recounts the research into Titan and the planning that led up to that encounter.

    http://www.thespacereview.com/article/1722/1

  • ljk February 25, 2011, 2:14

    http://www.technologyreview.com/blog/arxiv/26425/?ref=rss

    Why Earth and Titan Share Twin Atmospheres

    Earth and Titan have thick, nitrogen-rich atmospheres. That’s because both formed from the leftovers of cometary impacts, say planetary geologists.

    kfc 02/23/2011

    Saturn’s moon, Titan, must have formed in an entirely different way to Earth and yet they share one thing in common: thick, nitrogen-rich atmospheres that are seething with organic compounds.

    Today, Josep Trigo-Rodriguez at the Universitat Autònoma de Barcelona and Javier Martín-Torres at the Centro de Astrobiología in Madrid, both in Spain, point out that this might be an important clue. Their thinking is that common features point to a common past, meaning that the atmospheres of Earth and Titan must have formed in similar ways.

    At first glance, that seems unlikely. The conventional thinking is that the Earth formed in the inner part of the Solar System from the accretion of rocky planetesimals. Titan, on the other hand, formed in a melee of comet-like iceballs that orbited Saturn in the early Solar System.

    Nevertheless, Earth’s early atmosphere has always puzzled planetary geologists. One theory is that it formed from the outgassing of rocks as they bound together into the early Earth. But these rocks are thought to have been relatively poor in light elements such as hydrogen, carbon and nitrogen because these would have been preferentially blown away from the inner disc of the early Solar System.

    So it’s a surprise to see similar distribution of these elements in the atmosphere of Titan which formed from iceballs much further away.

    Trigo-Rodriguez and Martín-Torres conclude that the similarity means that Earth’s atmosphere must also have formed from comets, probably during the late heavy bombardment, a period some 4 billion years ago when the inner Solar System is known to have been showered with ice and rocks from further away.

    That seems sensible. Indeed it matches the conclusions from another line of thinking: isotopic analysis of the ratio of N14 and N15 in the Earth’s atmosphere.

    And that means it looks increasingly likely that life on Earth, made of star stuff, has evolved breathing comet gas.

    Ref: http://arxiv.org/abs/1102.4198: Clues On The Importance Of Comets In The Origin And Evolution Of The Atmospheres Of Earth And Titan