JPL: What is Consuming Hydrogen and Acetylene on Titan?

[bystander]

What is Consuming Hydrogen and Acetylene on Titan?
NASA JPL Cassini Equinox Mission (2010-190) - 03 June 2010

Two new papers based on data from NASA's Cassini spacecraft scrutinize the complex chemical activity on the surface of Saturn's moon Titan. While non-biological chemistry offers one possible explanation, some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan's surface. According to one theory put forth by astrobiologists, the signatures fulfill two important conditions necessary for a hypothesized 'methane-based life.'

One key finding comes from a paper online now in the journal Icarus that shows hydrogen molecules flowing down through Titan's atmosphere and disappearing at the surface. Another paper not yet online now in the Journal of Geophysical Research - Planets maps hydrocarbons on the Titan surface and finds a lack of acetylene.

Hints of life found on Saturn moon
New Scientist - 04 June 2010

Two potential signatures of life on Saturn's moon Titan have been found by the Cassini spacecraft. But scientists are quick to point out that non-biological chemical reactions could also be behind the observations.

Titan is much too cold to support liquid water on its surface, but some scientists have suggested that exotic life-forms could live in the lakes of liquid methane or ethane that dot the moon's surface.

In 2005, Chris McKay of NASA's Ames Research Center in Moffett Field and Heather R Smith of the International Space University in Strasbourg, France, calculated that such microbes could eke out an existence by breathing in hydrogen gas and eating the organic molecule acetylene, creating methane in the process.

This would result in a lack of acetylene on Titan and a depletion of hydrogen close to the moon's surface, where the microbes would live, they said.

Now, measurements from the Cassini spacecraft have borne out these predictions, hinting that life may be present.

[bystander]

Titan's atmosphere oddity consistent with methane-based life
ars technica - 05 June 2010

Something strange is afoot in the atmosphere of Saturn's moon Titan, according to data sent back from the Cassini mission. Data returned from a spectrometer on Cassini indicates that there's a large flux of hydrogen in the moon's atmosphere, with the gas forming in the upper atmosphere and being removed from the atmosphere at Titan's surface. We don't currently know what process is ensuring its removal, but the amounts of hydrogen being taken out of the atmosphere are consistent with an earlier proposal of methane-based life.

Titan's atmosphere is rich in hydrocarbon compounds, and chemical changes in the upper atmosphere are driven by the arrival of ultraviolet light from the sun. One of the expected results of the UV exposure is the liberation of molecular hydrogen from methane via a process that produces more complex hydrocarbons. With little oxygen to react with, the molecular hydrogen should remain stable. Some of it will escape into space, but a new paper¹ indicates that a substantial amount of that hydrogen migrates down through the atmosphere towards Titan's surface.

Since it's not accumulating there, some chemical process must be removing it from the atmosphere; right now, we don't know what that process is, and, as NASA's own news piece on the topic notes, the first option for scientists is to consider simple chemistry.

However, the abstract of the paper notes that this level of hydrogen consumption is consistent with an earlier prediction of methanogenic life. In short, the life would get its energy by "burning" the hydrogen with a carbon source instead of oxygen, releasing methane (CH4) in the process. The source of the carbon is where a second paper² (not yet online) comes in. Models of Titan's upper atmosphere suggest that significant amounts of acetylene should be produced by the reactions there, and this would provide an excellent source of carbon to any hypothetical metabolisms. The surprise of the second paper is that there's very little acetylene to be found on Titan's surface.

Two chemical enigmas certainly don't constitute life, and the authors of the latter paper provide a variety of ways to account for the acetylene shortage that don't involve an organism. It's also important to remember that there won't be anything resembling liquid water on the surface of Titan, so anything alive there would have to be living in a methane/ethane soup (not to mention at temperatures nearing -200°C).

1. Molecular hydrogen in Titan’s atmosphere: Implications of the
   measured tropospheric and thermospheric mole fractions, Strobel
   • Icarus, 15 March 2010. DOI: 10.1016/j.icarus.2010.03.003
2. Detection and Mapping of Hydrocarbon Deposits on Titan, Clark et al
   • Journal of Geophysical Research - Planets, 26 April 2010,
     DOI: 10.1029/2009JE003369 (not yet online) (JHU preprint)

[makc]

got the news from here via twitter today, this kind of synchronicity definitely means good journalist work rather than real breakthrough. I mean papers are dated 15 March and 26 April but not a word in the news until somebody decided to make big news out of it also, these scientist guys are so determined to find life on titan since the moment they knew it has athmosphere, that it just may be them trying too hard to prove it.

[bystander]

Both papers are in press (not yet published) and the second isn't even available online, yet (the doi link doesn't work).

[makc]

oh yeah, and this is important bit:

Two chemical enigmas certainly don't constitute life, and the authors of the latter paper provide a variety of ways to account for the acetylene shortage that don't involve an organism

hate to be a party pooper, but this is not even going to be taken serious by creationists.

[bystander]

Weird Chemistry on Titan *Could* Be a Sign of Methane-Based Life
Discover Bllogs | 80beats | 07 June 2010

If there were life on the Saturnian moon of Titan, the thinking goes, it would have to inhabit pools of methane or ethane at a cool -300 degrees Fahrenheit, and without the aid of water. While scientists don’t know just what that life would look like, they can predict what effects such tiny microbes would have on Titan’s atmosphere. That’s why researchers from the Cassini mission are excited now: They’ve found signatures that match those expectations. It’s far from proof of life on Titan, but it leaves the door wide open to the possibility.

In 2005, NASA’s Chris McKay put forth a possible scenario for life there: Critters could breathe the hydrogen gas that’s abundant on Titan, and consume a hydrocarbon called acetylene for energy. The first of two studies out recently, published in the journal Icarus, found that something—maybe life, but maybe something else—is using up the hydrogen that descends from Titan’s atmosphere to its surface:

“It’s as if you have a hose and you’re squirting hydrogen onto the ground, but it’s disappearing,” says Darrell Strobel, a Cassini interdisciplinary scientist based at Johns Hopkins University in Baltimore, Md., who authored a paper published in the journal Icarus [Popular Science].

Erring on the side of caution, the scientists suggest that life is but one explanation for this chemical oddity. Perhaps some unknown mineral on Titan acts as a catalyst to speed up the reaction of hydrogen and carbon to form methane, and that’s what accounts for the vanishing hydrogen. (Normally, the two wouldn’t combine fast enough under the cold conditions on Titan to account for the anomaly.) That would be pretty cool, though not as much of a jolt as Titanic life.

The second paper, forthcoming in the Journal of Geophysical Research, addresses the second part in McKay’s equation: acetylene, the would-be food for Titan microbes. In November of last year, Cassini scientists predicted a high level of acetylene in Titans’ lakes, as high as 1 percent by volume. But this study, using the Visual and Infrared Mapping Spectrometer (VIMS) aboard Cassini, did not find that:

Models of Titan’s upper atmosphere suggest that significant amounts of acetylene should be produced by the reactions there, and this would provide an excellent source of carbon to any hypothetical metabolisms. The surprise of the second paper is that there’s very little acetylene to be found on Titan’s surface [Ars Technica].

Again, life is not required to account for the lower-than-expected level of acetylene. The team did find the molecule benzene, and there are possible chemical reactions that could make acetylene into benzene. But, as is the case with the hydrogen paper, scientists’ knowledge of chemistry would suggest that you’d need a catalyst or something more to speed up the reactions and burn through all that acetylene.

So something weird is going on down there. The big question—the life question—will wait for future data and probably future missions that allow researchers to unpack the peculiar chemistry of this massive moon. But we can’t rule it out.

• Related Content:
  
  80beats: New Take on Titan Hints at More Fuel for Potential Life
  80beats: New Evidence for Ice-Spewing Volcanoes on Saturn’s Moon Titan
  80beats: Hydrocarbon Lake on Saturnian Moon May Be a Hotspot for Alien Life
  80beats: On Saturn’s Moon Titan, It’s Raining Methane

New Cassini Findings Show Possible Signs of Methane-Based Life on Titan
Popular Science - 04 June 2010

[bystander]

Alien Life on Titan? Hang on Just a Minute…
Universe Today - 07 June 2010

Two papers released last week detailing oddities found on Titan have blown the top off the 'jumping to conclusions' meter, and following media reports of NASA finding alien life on Saturn's hazy moon, scientists are now trying to put a little reality back into the news. "Everyone: Calm down!" said Cassini imaging team leader Carolyn Porco on Twitter over the weekend. "It is by NO means certain that microbes are eating hydrogen on Titan. Non-bio explanations are still possible." Porco also put out a statement on Monday saying such reports were "the unfortunate result of a knee-jerk rush to sensationalize an exciting but rather complex, nuanced and emotionally-charged issue."

Astrobiologist Chris McKay told Universe Today that life on Titan is "certainly the most exciting, but it's not the simplest explanation for all the data we're seeing."

McKay suggests everyone needs to take the Occam's Razor approach, where the simplest theory that fits the facts of a problem is the one that should be selected.
...
McKay provided four possibilities for the recently reported findings, listed in order of their likely reality:

1. The determination that there is a strong flux of hydrogen into the surface is mistaken. "It will be interesting to see if other researchers, in trying to duplicate Strobel's results, reach the same conclusion," McKay said.
2. There is a physical process that is transporting H2 from the upper atmosphere into the lower atmosphere. One possibility is adsorption onto the solid organic atmospheric haze particles which eventually fall to the ground. However this would be a flux of H2, and not a net loss of H2.
3. If the loss of hydrogen at the surface is correct, the non-biological explanation requires that there be some sort of surface catalyst, presently unknown, that can mediate the hydrogenation reaction at 95 K, the temperature of the Titan surface. "That would be quite interesting and a startling find although not as startling as the presence of life," McKay said.
4. The depletion of hydrogen, acetylene, and ethane, is due to a new type of liquid-methane based life form as predicted (Benner et al. 2004, McKay and Smith 2005, and Schulze-Makuch and Grinspoon 2005).

Has life on Titan been discovered? No.
Bad Astronomy - 07 June 2010

There has been a bit of an uproar the past day or so that scientists have found evidence of life on Saturn’s giant moon Titan. As soon as I saw the press release I knew this was going to be a problem. So let’s be clear:

First, have we found life on Titan? No.

Have we found evidence that there might be life on Titan? Sorta. The results are preliminary and not yet confirmed; in fact, some of the evidence is from computer modeling and has not been directly observed.

Bear in mind as well that evidence is not proof. Evidence just means an observation was made that is consistent with life on the moon, but doesn’t say much else. There are non-biological explanations for the observations as well.

Of course, speculation is running rampant, so much so that Chris McKay, an exobiologist who studies Titan, has released an article clearing things up.

Have we discovered evidence for life on Titan?
CICLOPS - 07 June 2010

Recent results from the Cassini mission suggest that hydrogen and acetylene are depleted at the surface of Titan. Both results are still preliminary and the hydrogen loss in particular is the result of a computer calculation, and not a direct measurement. However the findings are interesting for astrobiology. Heather Smith and I, in a paper published 5 years ago (McKay and Smith, 2005) suggested that methane-based (rather than water-based) life – ie, organisms called methanogens -- on Titan could consume hydrogen, acetylene, and ethane. The key conclusion of that paper (last line of the abstract) was "The results of the recent Huygens probe could indicate the presence of such life by anomalous depletions of acetylene and ethane as well as hydrogen at the surface."

Now there seems to be evidence for all three of these on Titan. Clark et al. (2010, in press in JGR) are reporting depletions of acetylene at the surface. And it has been long appreciated that there is not as much ethane as expected on the surface of Titan. And now Strobel (2010, in press in Icarus) predicts a strong flux of hydrogen into the surface.

This is a still a long way from "evidence of life". However, it is extremely interesting.

[Ann]

A good way to make the general public pay attention to astronomy-related news is to hint that astronomers have found life elsewhere.

According to this kind of news reporting, the best way to create an interesting news item is to ask atronomers to present proof that life is not there on another planet. If such "negative proof" can't be found, reporters can write that "scientists can't rule out the presence of life on Titan" (Mars, Europa, Enceladus, whatever).

I think I read somewhere that some astronomers hypothezised that there might be some exotic life forms on Venus, which would of course be specially adapted to cope with the extreme conditions there. But who's to say that there aren't such life forms on Venus? We haven't proved that they aren't there, have we?

Not long ago I read about a humongous red supergiant star which was so cool that there was a lot of water vapour in its atmosphere. Doesn't water vapour sound life-friendly? Who is to say that there aren't life forms thriving in the atmosphere of that red supergiant?

And if there is life in the atmosphere of another star, then who's to say that there isn't life somewhere in or on the Sun? Have we looked? Shouldn't we assume that there is life in the Sun until we have proved otherwise?

And hey, what about the man in the Moon? How do we know that he isn't there? How carefully have we searched the Moon? Shouldn't somebody write an article right away with the headline, "The Man in the Moon Is There After All?"

What I find so extremely irritating about this kind of speculation is that it plays down the specialness of the Earth. Personally I'm convinced that the Earth is one planet in a million, if it's not one planet in a billion or trillion. But when reporters keep telling us that life on other planets is as common as fleas on a dog, then why should we bother to take care of our own world? Let the oil keep gushing out in the Guld of Mexico. Let gas pipelines explode in Texas. Let the Aral Sea dry out. Let's cut down the rain forests and let's turn fertile land into deserts. Who cares? It doesn't matter what we do to the Earth. We will be fine anyway. Hey, if there is life on Titan and on Venus, and there must be because it says so in the papers, then surely life will be fine on the Earth no matter what we do to the Earth?

Ann

[geckzilla]

You jump to some conclusions which are strange to me, Ann. The media loves to put news about aliens up because it's sensational and I don't think there's much more to it than that. And as far as our planet goes, we can complain about pipes exploding and oil spilling all we want but no one ever seems to make the connection between "I want cheap gas!" and the corporations who respond with "Let's make more gas... cheaply." No one to blame but ourselves. There's just too many of us. And you're not ever going to convince millions of people who make their living cutting down rain forests not to do so no matter how wrong it seems to you from the comfort of your computer chair. Save the planet - don't have kids. Heh.

[Ann]

Well, I'm irritated at this constant "we have not proved that life is impossible here" approach.

Just read today's AstronomyNow on line: http://www.astronomynow.com/news/n1006/08exo/

This is how the article starts:

Analysis of all 79 star systems known to have transiting exoplanets has revealed that only two could definitely not support life as we know it

Right. Only two out of 79 of these stars systems could definitely not support life. So that means, doesn't it, that the other 77 systems could support life, and since they could, they probably do? That could mean that 97% of those star systems contain a life bearing planet. Hey. Not bad.

I wonder, however, when we will start looking for positive signs of life instead of just saying that we can't absolutely rule out the presence of life on other planets.

Ann

[bystander]

Big difference between could and probably do.

[geckzilla]

Looking forward to your discoveries, Ann.

I know there are a lot of brilliant people out there doing their damnedest to brainstorm and come up with ways to find life out there. It's one of those aching questions that feels like it can't be answered too soon.

[Ann]

Geckzilla wrote:

I know there are a lot of brilliant people out there doing their damnedest to brainstorm and come up with ways to find life out there.

I don't think they are really trying to find life out there. I think they are coming up with ways to argue that there could be life in places where they know that there most likely isn't.

I have a book from the nineties at home, a book written at a time when it had just become possible to detect planets, and one astronomer quoted in that book speculates that it will be possible to distinguish between planets and brown dwarfs by looking at their orbits, because planets will follow circular orbits and brown dwarfs elliptical ones. So planets in other solar systems will be just like the dominant planets in our solar system, in other words. And because most other solar systems were thought to be like ours, they could also be assumed to have life-bearing planets.

It turned out that very many planets in other systems aren't following circular orbits. I realize why the astronomer fomulated his hypothesis, though. It's because planets are supposed to form out of the disk that feeds material onto the star, and that disk can be assumed to "orbit" the new star rather regularly. That's how astronomers reasoned in the 1990s, anyway. Brown dwarfs, however, were assumed to form independently from their own gas cloud, and afterwards they were thought to be captured by a larger star. That scenario would certainly be more likely to produce elliptical orbits.

Well, it turned out that the "planets follow circular orbits" hypothesis was just so much wishful thinking. And I think that the new hypothesis, the one saying that 77 out of 79 "hot Jupiter systems" could host lifebearing planets, is also mostly a wishful thinking product.

Think about it. What do we know about those other solar systems that we have detected? What do we know about their planets? Frankly we know so extremely little about them apart from their masses and their orbits. What we know about their masses isn't all that interesting, because the kind of equipment we have got is really only good for detecting large and massive planets, so the fact that we haven't found any Earth-mass, Earth-size planets so far is a pure selection effect. The way I see it, we have no reason whatsoever to doubt that Earth-mass, Earth-size planets exist out there in large numbers.

But what about orbits? Is that also a selection effect? I doubt it. I believe the orbits we have found may be typical of orbits in other solar systems, also those containing Earth-mass planets. Well, the hot jupiters may not be typical, because they are extremely easy to detect, so we may well have seen them because they are easy to spot, not because they are common. They may in fact be rare. But what about the elliptical orbits? Are they also rare? I don't think so myself. I think they are typical.

Anyway, this is my point. Astronomers look at 79 systems where the only thing we really know, the orbit of the dominant planet, is absolutely nothing like the orbits of Jupiter and Saturn in our own solar system. They look at 79 systems where the one factor we know about them makes them completely unlike our own system. Then they come up with computer models saying that 77 of these systems may contain a living planet just like our own. Is that serious science? Does it tell us anything about what those 77 systems are really like? No, the way I see it, it is mostly an attempt to make other solar systems seem like our own. Therefore it is mostly wishful thinking. If the stronomers really wanted to say something meaningful about those other planets, I think they should try to find out how likely it is for a hot jupiter system to have an Earth-mass planet following a circular orbit inside that solar system's habitable zone. But such calculations may produce depressingly low probabilities, so they seize on the fact that the probabilities they have come up with are not zero.

So I frankly don't think they are trying to detect life that way, I think they are grasping at straws and indulging in wishful thinking.

[The Code]

I think I read somewhere that some astronomers hypothezised that there might be some exotic life forms on Venus, which would of course be specially adapted to cope with the extreme conditions there. But who's to say that there aren't such life forms on Venus? We haven't proved that they aren't there, have we?

Not long ago I read about a humongous red supergiant star which was so cool that there was a lot of water vapour in its atmosphere. Doesn't water vapour sound life-friendly? Who is to say that there aren't life forms thriving in the atmosphere of that red supergiant?

And if there is life in the atmosphere of another star, then who's to say that there isn't life somewhere in or on the Sun? Have we looked? Shouldn't we assume that there is life in the Sun until we have proved otherwise?

Life on the Sun? Life on Venus? How do we go about looking? I think I'll give that trip a miss.

[bystander]

Astrobiologist tries to set the record straight about extraterrestrial life on Titan
Scientific American | Observations | 08 June 2010

Titan, Saturn's largest moon and the second-biggest natural satellite in the solar system, is an unquestionably interesting place. It's a world with a thick atmosphere and with lakes, fog and rainfall—only with liquid hydrocarbons rather than liquid water.

Titan would be even more interesting if a speculation made five years ago proved out: that the moon could be teeming with extraterrestrial life. Titan-based (Titanate? Titanic?) life could dwell in liquid methane and breathe gaseous hydrogen, just as so much Earthly life dwells in liquid water and breathes gaseous oxygen. Such organisms would consume hydrocarbons such as acetylene near Titan's surface, so their presence might be recognizable by a dearth of acetylene and hydrogen at the surface, Chris McKay and Heather Smith noted in Icarus in 2005.

A pair of new studies provide evidence for such depletions of acetylene and hydrogen, stirring up a sudden frenzy of public interest in Titan, including a characteristically bombastic treatment from the British press. The Telegraph grabbed readers' attention with the headline, "Titan: Nasa scientists discover evidence 'that alien life exists on Saturn's moon'." On Twitter, Carolyn Porco, lead scientist on the imaging team for NASA's Cassini spacecraft, bemoaned the headline and reported that she "just got an e-mail from someone 'applying' to be among those folks we send to Titan."

Now McKay, of the NASA Ames Research Center in Moffett Field, Calif., has seen fit to clear the air himself, making plain that extraterrestrial life on Titan is but one possible explanation of many—and far from the most likely.

The astrobiological significance of the lack of acetylene at Titan's surface, as measured by Cassini, rests on the finding that hydrogen seems to be disappearing at the surface as well, McKay wrote on the Cassini imaging team's Web site. "This is the key that suggests that these depletions are not just due to a lack of production but are due to some kind of chemical reaction at the surface." (Ethane, another possible fuel for methanogenic life on Titan, is also depleted.)

Nevertheless, the key finding that hydrogen is vanishing at ground level on Titan needs to be confirmed before jumping to any conclusions. The most plausible explanation for the new results, according to McKay? "The determination that there is a strong flux of hydrogen into the surface is mistaken." Other possible mechanisms for the presumed hydrogen loss include atmospheric processes that transport hydrogen out of the upper atmosphere, or nonbiological chemistry at the surface, driven by some unknown catalyst.

The existence of methane-based life churning through hydrocarbons and gaseous hydrogen is the fourth most likely explanation out of four, according to McKay. "This is a still a long way from 'evidence of life'," he wrote. "However, it is extremely interesting."

Possibilities for methanogenic life in liquid methane on the surface of Titan

• Icarus, Vol 178, No 1, 01 Nov 2005, DOI: 10.1016/j.icarus.2005.05.018