I love what William Bains (University of Cambridge) has to say about extraterrestrial life and how it might appear to us. “Wouldn’t it be sad if the most alien things we found in the galaxy were just like us, but blue and with tails?” He’s thinking, of course, of some science fiction evocations of aliens and their general similarities to our own species, perhaps the result of Hollywood budgetary constraints as much as lack of imagination. But Bains is interested in alien life for more than cinematic reasons. He’s looking hard at Titan, and envisioning what life there might look like.
Image: A flat, calm, liquid methane-ethane lake on Titan is depicted in this artist’s concept. Copyright 2008 Karl Kofoed.
Life on Titan would be, by our standards, a bit unusual. Says Bains:
“Life needs a liquid; even the driest desert plant on Earth needs water for its metabolism to work. So, if life were to exist on Titan, it must have blood based on liquid methane, not water. That means its whole chemistry is radically different. The molecules must be made of a wider variety of elements than we use, but put together in smaller molecules. It would also be much more chemically reactive.”
Bains will discuss these matters at the 2010 meeting of the Royal Astronomical Society in Glasgow, a gathering that meets all week, and one whose results we’ll follow with interest. As to Titan, Bains’ talk acknowledges that the distant moon presents an enormous challenge for astrobiology, but perhaps not an insurmountable one. Although a surface temperature of -180 Celsius could not support life as we know it, we do have liquid methane and ethane available in ponds and lakes on the surface. Sunlight is only a tenth of a percent as intense on Titan’s surface as on the surface of the Earth, so energy is a problem, meaning slow-growth organisms like lichen are more theoretically plausible than fast movers.
Yet forms of life might emerge. And it’s entertaining to think of a true Titanian alien as depicted by some ambitious film director of the future. Says Bains:
“Hollywood would have problems with these aliens. Beam one onto the Starship Enterprise and it would boil and then burst into flames, and the fumes would kill everyone in range. Even a tiny whiff of its breath would smell unbelievably horrible. But I think it is all the more interesting for that reason.”
It’s hard to disagree. Aliens in the cinema are notoriously anthropomorphic or, at best, suggest odd forms of other Earth species more than serious attempts to tackle extraterrestrial beings. On Titan we have to think about the solubility of chemicals in liquid methane, which is limited and dependent on molecular weight. A metabolism functioning in liquid methane would have to be built of smaller molecules than in terrestrial biochemistry, with molecules having more than 6 non-hydrogen atoms being essentially insoluble. We would expect, says Bains, sulphur and phosphorus in diverse and unstable forms, and other elements, such as silicon. All of which leads to the potent creature described above.
Maybe the excellent ‘Exoplanets Rising’ conference jacked my expectations up to unreasonable levels, but as the RAS 2010 meeting gets going, I’m going through the site looking for evidence that video streaming or archiving of these sessions will be forthcoming. Let’s hope so. UC Santa Barbara’s Kavli Institute for Theoretical Physics did at terrific job in getting the exoplanet talks posted the next day, so that we now have a complete archive of the ‘Exoplanets Rising’ sessions, including posters. In doing so, they’ve set a high standard for future conferences. RAS take note!
We cannot even transport earth life from the deep oceans to our sea surface ships, let alone alien life.
Yes, methane is a very poor solvent. It’s non-polar, a severe limitation. And silicon is a very distant second best to carbon. I’m not sure you can have complex life based exclusively on hydrocarbons and silicon… but we won’t know until/unless we have looked closely at places like Titan.
Alex, exactly. Bains is right, of course — Hollywood anthropomorphizing is not only because until recently you had to use actors, but also because it’s easier to identify with (or hate passionately) something that looks more or less humanoid. I wrote about this in my book and I’ll also have an article on the topic of recognizing alien life on Friday, in the Science in My Fiction blog. I’ll post the link here when it appears.
Titan is too cold for life.
The Arrhenius equation: k = A exp(-E/RT)
Chemical reactions are simply too slow in Titan’s temperature regime for life to have emerged.
As far as civilization capable sentient life goes, it’s actually quite likely they would have a passing resemblance to us. Non-sentient life gets more interesting.
Hi All
Kurt9 I think that depends on the reactivity of the chemicals – what falls apart too quickly at 310 K may work just fine at 93 K. Thus the news-bite/opinion-piece Paul is discussing.
My response to this coverage at a couple of other fora has been this…
Some more adventurous sulfur-based lifeforms on planets with NOx air and sulfuric acid oceans speculate in their science literature about cryogenic (i.e. below sulfur’s melting point) lifeforms based on liquid hydrogen monoxide, carbon polymers and elemental oxygen chemistry… and their ideas are condemned by conservative thinkers as wildly speculative and ‘science ficiton’.
And which chemical reactions do you mean ? There are reactions that are too fast at our temperatures ( or not possible at all because the reactants would fall apart before they could meet ), but might be reasonably fast at -180
“Titan is too cold for life. ”
Not so long ago, most would have said that Enceladus would be too cold for liquid water. Predictions of water geysers erupting from such a small, cold moon, would’ve been met with incredulity.
Just found a scale pic of Enceladus that makes me, as a Brit, very happy: http://www.windows.ucar.edu/saturn/moons/images/enceladus_size_england_big.jpg
That scale pic of Enceladus is great! Thanks. I do wonder if it will make Enceladus seem larger than it really is, as, in the United States, the UK often seems bigger than it really is too. (Due its historical and cultural importance that is — no offense whatsoever is intended!) In the States, it is sometimes hard to remember that the entire UK, including all of England, Wales, Scotland and N. Ireland, is only a third the size of Texas!
Whoops, I left out the clause “To Americans” in my last comment. I didn’t mean to sound like I thought that everyone reading this blog was an American.
To do penance, here’s a link to some elaboration by William Bains on the main subject of Paul’s post:
http://www.williambains.co.uk/astrobio.htm
It is conceivable that the combination of cold and non-polar solvent will allow the formation of stable complex structures bound together not by covalent bonds, but by weaker polar interactions, similar to the hydrogen bonds that are so important in our biochemistry. This would be an entirely different kind of biochemistry.
Hi Adam;
It is interesting to consider that at temperatures below 100 K, any lifeforms might utilize superconductivity in some of the thermodynamic activities within their bodies.
Athena, regarding chemical reactions in ultracold environments, at the link below is a fascinating story at Science News.
http://www.sciencenews.org/view/generic/id/57425/title/Superchilly_chemistry
At the second link is a great Science News story regarding indirect evidence that some aquatic animals may go their entire lives without oxygen.
http://www.sciencenews.org/view/generic/id/58154/title/Multicelled_animals_may_live_oxygen-free
Slightly off-topic, but related:
has there been any recent and more conclusive news on the presumed fossil nano-bacteria in the famous Mars meteorite ALH84001 ?
Not so long ago there was a brief excitement that more and particularly more convincing evidence was found for this:
http://www.nasa.gov/centers/johnson/news/releases/2009/J09-030.html
And (big) PDF:
http://www.nasa.gov/centers/johnson/pdf/403089main_7441-1.pdf
Quotes:
“strong evidence that life may have existed on ancient Mars”
“None of the original features supporting our hypothesis for ALH84001 has either been discredited or has been positively ascribed to non-biologic explanations”
“the biogenic hypothesis has been further strengthened by the presence of abundant biomorphs in other martian meteorites”
Is the jury still out on this one, any white/black smoke?
I am always a little disturbed by comments like
“Sunlight is only a tenth of a percent as intense on Titan’s surface as on the surface of the Earth, so energy is a problem, meaning slow-growth organisms like lichen are more theoretically plausible than fast movers.”
There, again, we are talking about OUR experience in how life is expected to behave. If life forms that have a methane-ethane based “blood”, possibly a silicon based chemistry (like ours is carbon), I think there most certainly would be other sources of energy, external and cellular, that would produce some “fast movers”, Probably wilder than anything we could imagine. This is one of the most fascinating things to think about – what would the Krebs Cycle be like in life forms that live and evolve on Titan? I’m getting my old Leninger Chemistry book out and fiddle around.
I agree with Connie. Sunlight alone, on Earth or Titan, does not produce enough energy for fast movers. You don’t see a lot of plants running around. There aren’t even any photosynthetic fish. It is the energy stored in oxygen that permits animal life on Earth. Whatever the equivalent of oxygen on Titan might be, if it can build up in the atmosphere or in the liquid whatever-it-is in the lakes, it can sustain a population of “fast-movers”. The ratio of plant to animal life per surface area might be larger on Titan, but what animals there are can be just as active as those on Earth, alien metabolism permitting.
I think on Earth the limit for power density in animals is given by the efficiency of breathing, and birds are at the top of this particular ladder (as were the dinosaurs). The amount of oxygen in the atmosphere, AFAIK, is limited not by animal consumption, but by plant combustion, aka forest fires. Thus, animal life on Earth is probably not limited by solar energy at all.
What could this oxygen equivalent be? It needs to be about as soluble in Titan’s lakes as oxygen is in seawater. It needs to yield about as much energy when reacted with Titan biomass (the animal food) as oxygen does when reacting with Earth biomass. And it needs to be sufficiently inert to not react in an uncontrollable manner. I think this is a pretty tall order, and there might not be such an oxygen equivalent. If so, any life on Titan would be strictly plants only.
Presumably Huygens puts some kind of upper limit on the ubiquity of large-sized life on Titan — the images it sent back didn’t, for example, show anything like trees or elephants, or a landscape that seemed altered by anything other than geologic processes. The best bet for life may be lakes.
This wikipedia page is relevant and interesting: http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry
It seems to make a good case for silicones in biochemistry.
I’m not sure if you and I have the same Wikipedia, Dan. The article (and my own knowledge of organic chemistry) argue quite powerfully that silicon biochemistry is a very, very distant second best, if that.
I remember reading a story once about a large planet (It would be called a super-Earth now) which had a hydrogen atmosphere and non-humanoid aliens living on it that where very sturdy because of the high gravity. They were breathing hydrogen. The plucky aliens ended out flying a hot-hydrogen balloon, which is pretty much all I remember about the plot.
It was brought back to mind by the section in the above Wikipedia article which explains the sulphur-nitrogen biochemistry, which apparently allows for hydrogen as an oxygen equivalent. Not sure if the story elaborated on it to that extent. Does anyone recognize that story?
James, I have no problem with life in cold temperatures. But it will be slow — other things being equal, catalytic speed is proportional to temperature.
Eniac, I believe the story you described is Hal Clement’s Mission of Gravity. If you read my article about aliens which just appeared in Science in my Fiction, you will see an unknown artist’s image of the story’s alien protagonist, Barlennan of Mesklin:
You Only Find What You’re Looking For
http://crossedgenres.com/simf/2010/04/16/you-only-find-what-youre-looking-for/
Also, oxygen cannot exceed a certain percent in an atmosphere. When it does, the slightest friction sets off conflagrations (Stan Robinson had a dramatic, haunting scene in Red Mars that hinges on this). Incidentally, my article about genetic engineering in H+ magazine has been scheduled for next week. The title is Miranda Wrongs: Reading too Much into the Genome.
Athena: Yes, that’s it. Thank you. The planet’s name is Mesklin, and the inhabitants have a fear of heights even just a few inches. I much enjoyed that story, because of the meticulous presentation of a completely alien, yet plausible world. It may be criticized for failing to follow up with completely alien minds, but you have to be careful what you ask for…
Your point about oxygen is important, which is why I mentioned forest fires. Similarly, oxygen concentration in seawater is limited by its solubility. Any alien oxygen equivalent would have to have properties similarly favorable (or better) as a latent energy source. As I said, this might be a tall order.
If the oxygen equivalent is good in the sea, but not in the atmosphere, we could have active animals in the sea, but not on land. If it does not work in the sea, either, we get only plants. If it works only in the atmosphere, we could have an interesting situation. Animals would have to evolve from land plants, instead of coming out of the sea. Thus, the principal scenarios different from that on Earth would be plants only, fish only, and active plants.
I disagree that biochemistry has to be slow in low temperatures. As has been said, there are fast reactions at low temperature, they would just be different ones.
Eniac, the only reactions that I can think of that go faster in low temperatures are in superconducting materials. So if you can have life based on that, its temperature optimum would be low.
Mesklin was 61 Cygni A. 61 Cygni, aka Bessel’s Star, is actually a K-dwarf binary with the largest observable proper motion (which made it tempting to postulate planets around the primaries).
Hi All
One of my fave stories of world-building is “Mission of Gravity”. Had some of the wildest oceanic phenomena as the methane evaporated season to season. Clement wrote an essay discussing how he dreamt up Mesklin – “Whirligig World” – which is now collected with the other stories/novels in “Heavy Planet”. The sequel, “Starlight”, is set on a more conventional super-massive planet, Dhrawn, around Lalande 21185. It’s a shame both planets can’t exist as far as the latest astrometric data from both stars implies, but I doubt that would’ve troubled Harry Stubbs terribly much.
I see allot of comments that state that the temperature on Titan is too cold for life. Yet within just the past 50 years we have discovered life at the bottom of our oceans living at extreme pressures and temperatures. We have animals that produce chemicals to keep their blood from freezing. To believe in life beyond our planet we must completely clear our minds of the restrictions we have set on what life can be comprised of and the conditions it can survive in. We know what we know here and as humans tend to assume certain things (because we think we have everything pretty well figured out). When in reality we know very little. We are trying to figure out the seperate elements of the atom while at the same time were trying to make models of our universe. If we can look at these two extremes in size with no sense of that’s imposible, why can’t we be more open about the wide parameters that life could evolve in? When will we quit beliving that life only exists on Earth at 75 deg Farenheit?
I believe that our collective thinking on alien life dosn’t amount to much. Wasn’t everything we knew about vulcanism and it’s after effects “turned on it’s ear” by the Mt St Helen’s event?