T Nation

The Living Worlds Hypothesis


I came upon this article today. I thought it would be interesting in light of recent discussions about life, evolution and the beginning of life. If nothing else, doing more investigation of our own solar system might help us answer some of the tougher questions in science today.

[center][b]The Living Worlds Hypothesis[/b][/center]

Interview with David Grinspoon, Principal Investigator for NASA's Exobiology Research Program and author "Venus Revealed" and "Lonely Planets"

Ref: http://www.astrobio.net/news/print.php?sid=1720

When the Cassini-Huygens mission parted Titan's smoggy veil, it revealed a familiar and yet utterly alien landscape, one where now-dry methane rivers carved out channels in mountains of ice. There's no evidence for biology on Titan's frozen terrain, but in this interview with Astrobiology Magazine, David Grinspoon ponders whether life could exist there today.

Saturn's moon Titan is enveloped in a thick orange haze, and the organic particles that make up that smog have been raining out of the atmosphere and down onto the surface for millennia. This rich chemical brew is thought to be ripe for life's origin, similar in some aspects to Earth in its earliest days.

Pre-biotic potential aside, a paper recently published in the journal Astrobiology by Dirk Schulze-Makuch and David Grinspoon investigates the possibility for organisms to exist on Titan today. Astrobiology Magazine's Leslie Mullen sat down with David Grinspoon to talk about life on Titan, what sort of food they could be dining on, and how they might make their presence known to us.

Astrobiology Magazine (AM): You recently published a paper investigating the possibility of life on Titan, based on what we know about the moon today.

David Grinspoon (DG): The paper looks at the requirements for life in the most basic sense, and what kind of planets you should look for, and then asks if Titan fits the bill. People have asked that question before, but now that we've had the first Cassini and Huygens results, and Titan's environment is emerging a little more clearly, we thought it would be worth re-examining it.

People talk about Titan and astrobiology all the time, but it tends to be Titan as the laboratory for the pre-biotic Earth. It's got nitrogen, it's got organic chemistry. We've known that for a long time, and that was a large part of the motivation for sending these missions, Cassini and Huygens, to examine the pre-biotic chemistry.

But people haven't talked much about the idea that something might be living on Titan today. I think mostly because it's so cold there, and chemical reactions just proceed too slowly. But Titan turns out to be an exceedingly active planet. We see evidence for cryovolcanism, and for active meteorology. So there's a lot going on there. There are energy sources, flows, gradients, things changing, and different chemicals coming into contact.

I think the most basic requirements for life come down to needing a source of energy of some kind, needing liquids, and needing some basis for complex chemistry. And we conclude that Titan has all three. Obviously it has liquids - if you've got cryovolcanism, you've got liquid reservoirs of water, or water with ammonia antifreeze, near the surface that occasionally is erupting to form those flows. There are also liquid hydrocarbons silting the surface in places.

What's really new in our paper is that we go into the question of energy sources. If there's life there, what's it going to eat? What kind of food is there? And it turns out there's abundant food because of all this photochemistry in the upper atmosphere, where methane is being turned into other organic molecules. Some of those organic molecules are very energy-rich, and one that we consider in the paper is acetylene. We know it's being made in the atmosphere, we know it's raining down on the surface, and it's been detected at the surface with the Huygens probe. We calculated that, if acetylene is reacting with the hydrogen gas to turn it back into methane, quite a bit of energy is being released. So that's our basis for saying there is something to eat on Titan. We don't know if there are any customers, but there's something on the menu.

AM: So there's acetylene rain from the sky that's produced by the breakdown of methane…

DG: By ultraviolet light and also by interactions with Saturn's magnetosphere. There's a lot of energy up there. Then the acetylene is raining down and getting buried. Then, potentially, subsurface organisms use the acetylene, and in the process reconstitute the methane, which is going back up into the atmosphere. That's why we called our paper, "Biologically enhanced energy and carbon cycling on Titan," to give this idea that it's part of a cycle. It potentially solves the problem of why there's methane on Titan when we know it's being destroyed.

AM: And the areas of cryovolcanism provide possible havens for life?

DG: You've got to think about where are the places where it would be good to live on Titan. You would be overcoming the cold in part if you go to the hot springs. I like hot springs, and I think that Titan organisms would like them too. I think especially at a place like Titan, hot springs are going to be really nice if you're any kind of a carbon-based life form.

AM: It seems such a world of extremes, because you have acetylene, which makes me think of acetylene torches that make these intensely hot flames, and then you have this frozen world. It's fire and ice.

DG: Acetylene doesn't seem like something you'd want to eat, but on the other hand, the fact that we associate it with acetylene torches is an illustration that there's a lot of energy there. Because Titan is so cold, chemical reactions that we think of as explosive on Earth because they proceed so rapidly might proceed at a moderate pace on Titan. In order to have life, you want to have chemistry that's not so active that everything's just exploding and burning up, but not so unreactive that it's just sitting there. It's got to be within a certain range. And certain kinds of reactions that on Earth might be too active for biochemistry might be just right on Titan where it's colder.

AM: There's no life on Earth that uses acetylene?

DG: I don't believe there is, but that's not surprising because acetylene is not stable on Earth because of all the oxygen. That combination is explosive, so you don't have acetylene sitting around anywhere. On Titan, there's no free oxygen, so the acetylene could react with hydrogen to create methane.

AM: Your paper also mentioned the chemistry of radicals as another possible source of energy on Titan. I know oxygen radicals are thought to be really bad for life on Earth.

DG: Radicals are very reactive because they're chemicals that are out of electronic balance; they're missing electrons or they have too many electrons, so they're frantically looking around for anything to react with and in the process they can destroy things. We think of radicals as these things that cause cancer, because when you get them in your cells they'll react with anything. But that very reactivity, if it could be tamed, could be a powerful energy source for biology. One way to tame it might be to exploit it in a cold environment, where the chemistry is going to be much slower. This is separate from the acetylene argument, but we do point out that there are certain kinds of chemistry that could potentially, at the cold temperatures of Titan, proceed at appropriate rates to be good biological energy sources.

AM: I get a sense that there's this whole spectrum of processes in biology, and some of them don't quite work right on Earth - they're too dangerous or energetic - but maybe part of that spectrum could work much better on a different world like Titan.

DG: Exactly. I think that's the way we need to think, because otherwise we're just projecting our own preferences and our own type of life elsewhere. Then we're always going to look for worlds just like the Earth. Maybe that's the only kind of life out there, but I doubt it. If you think of life in the abstract, as just a controlled chemical reaction that breeds more complexity and then gets to be self-replicating and evolves, then there are probably lots of kinds of life. But you have to think outside the box about what would be the appropriate kinds of chemistry in other environments, and it's harder to do, because you can't just use terrestrial examples.

AM: But at the same time, there might be clues within our own terrestrial examples.

DG: There might well be, and thinking about this kind of thing is valuable because it forces us to consider which aspects of terrestrial life are likely to be universal, and which are peculiar to our own environment. But ultimately we're not going to find the answers to these questions by theorizing and writing papers and making models, we're going to find the answers by going out there and finding it. Science is fun and interesting and worthwhile, but we'll find the answers through exploration.

AM: In searching for life, people often think clues can be found in the isotopes of elements like carbon, since some forms of life on Earth preferentially eat lighter carbon isotopes. But you've said that the isotopic compositions indicative of life are not necessarily going to be the same for Earth and Titan.

DG: You've got to be careful there. I think it's likely that life will result in distinct isotopic signatures, and it's one of the kinds of clues that we should be looking for. At the end of our paper, we list some possible biosigns on Titan, and unusual isotopic fractionation is one of them. But we don't know what kinds of isotopic fractionations alien life will make. Also, we don't know what other fractionations are naturally occurring on Titan. Gases escaping from the atmosphere fractionates the carbon, but we don't know how much this process affects the isotopes. The problem is not well enough constrained to rule out life, or to prove life at present.

AM: So how does Titan fit in with your idea about living planets?

DG: Cassini saw that Titan has all these processes going on, mixing things up and releasing energy. The main point about the living worlds hypothesis, as I call it, is that planets that are geologically and meteorologically alive are much more likely to be biologically alive as well, especially if they have been continuously active throughout their history. An active surface is not a bio-indicator in the sense that it says, "Ah, there's life here." But sometime in the future, when we can do comparative astrobiology and we have lots of worlds with life and others that don't have life, I think we're going to find that the ones with life are all active planets.

AM: The phrase "living world" reminds me of something you said before, that "A planet and its life will co-evolve."

DG: Well, on Earth they certainly have. It's not just that Earth is a nice place to live and then life is here and isn't it lucky. Life has made Earth the way it is to a large extent. That's the Gaia hypothesis, and the living worlds hypothesis is closely related to the Gaia hypothesis, just trying to generalize it to other planets.

AM: So life created Earth just as much as it created us, and therefore you might never find another planet exactly like Earth out there. And then I look at Titan, and I wonder whether life could be intertwined with any of the processes there.

DG: I think it's possible. If there is all this energy being released by these powerful chemical reactions, with stuff raining out of the sky like acetylene and other compounds, some of that energy could be going into metabolism, the work that the organisms do to power themselves. Also, some of that energy is going to be waste heat released into the environment, but in a place like Titan, what we think of as waste heat might not be all that wasteful. Organisms can use it to melt their own little watering holes. Then you can even imagine a sort of Gaian mechanism where organisms are helping to create the environment that helps keep the organisms happy.

Taken to an extreme, you could imagine that this large-scale melting we see on Titan is the result of organisms. I'm not claiming that we can confirm it, but imagine for an instant that Titan is loaded with organisms. I don't think we can rule this out. So imagine life is all over the place, and acetylene and other compounds are being turned back into methane and heat is being released… well, that could end up melting a lot of stuff. If acetylene is concentrated in certain geologic deposits, which no doubt it will be, maybe there are places where the collective action of that life is melting a lot of stuff and helping to lead to the high degree of activity on the surface. It's pretty "out there" as an idea, but I don't think it's impossible.

If you go back to this living worlds hypothesis and look at a planet like Earth, where life has radically altered the planet, one possibility is that life always radically alters its planet. I think it's quite possible that we won't find life on planets that have not been radically altered by life.


I've always thought at some point in our history we'll run into life not of Earth. Just don't know when. Maybe hundreds of years from now. Maybe next Tuesday.

We have our perspective what it takes for life to exist. Who know's what could be out there. Maybe nothing but maybe....something beyond our comprehension, or maybe just microbes.


One question is: Is life rare or common?

Currently, we know of life only here, on Earth; which makes it appear to be quite special.

If it turns out that there's life somewhere else in the solar system, we might have to conclude that life is probably relatively common in the universe.

It doesn't matter if it's only bacterias or microbes. The simple fact that self-replicating chemical structures would've appeared somewhere else, especially so close by, would lead to the conclusion that there probably wasn't anything special about the appearance of life on Earth. The universe might simply be set up to be "life rich."

Having it appear twice (or more) in a single solar system would settle many scientific debates on whether life requires an enormous amount of parameters to be just right (ie, The Rare Earth position); or if life "finds a way" and appears in a multitude of form as long as there's a sufficient amount of varied chemicals and energy available.

Unfortunately, with the recent goals of manned missions to the moon and then Mars, it seems it'll take a really long time before we know for sure.


If life is common, and adaptive to its surrounding I would have to ask why life didn't survive on the other planets that are so close by?

(This is not a comment for arguments sake. I am really curious to find out your take on that)


It depends on your definition of life. We tend to think of life in terms of our own carbon-based existence. But what if the "life" on other planets is not carbon-based? What if it is silicon-based? Can we then use our definitions to determine what is life? What if it is our limited frame of reference that is keeping us from understanding life on other planets? Some food for thought.


I term life in the sense of something that can begin to gain intelegence, similiar to us. It is not required that it be fully carbon based. The only requirement would be advancement.


Because the planets have to be equipped to support the kind of life we're talking about. This includes food supply (the correct elements and molecules), average temperature, and consistency of temperature, as well as pressure and gravity.


I understand what you are saying, but what if that "life" is so radically different that what we are familiar with that we don't recognize the intelligence that it has? What if our frame of reference doesn't allow us to understand and recognize what that life's ability to advance truly could be? What if it is so beyond our ability to comprehend that it could be standing right in front of us and we wouldn't know it. We might be looking right at signs of life from its perspective, but we just can recognize it because of our own limitations.

I know I am going pretty far out there, but I would think that it would be pretty cool to find something in the universe that totally redefines what we term as "life".


This is what I mentioned earlier. Maybe the kind of life we are talking about may not be the kind of life that exists on these planets. Then again, maybe it is and I am wrong. Not like that hasn't happened before. LOL


I understand that. The only problem is how much change could have happened in our solar system to have allowed these planets to once have life, but now they are void of such requirements.

I should have probably stated the problems that I have with such a con cept at this point. I am such searching for the possibilities for an idea to even be concievable.


If it is that advanced I don't think we would ever have to worry about finding it.


I'll bet those little organisms on Titan are arguing with each other about if they evolved or were designed by some intelligence. They are passionatly sending e-mails back and forth on their methane based internet, calling each other idiots and non-believers. Maybe that is a sign of life as well.


I've said this before in an older thread, and I'll say it again.

I bet that life is not all that rare. Perhaps lifeforms organized to the degree that we are will be rare, but life in general, ie organized and self-replicating and adapting biological structure, just might turn out to be not so rare after all.

Even on our home planet there are lifeforms who survive in the most unlikely of places and ways. I would not be surprised at all if life turned out to be relatively ubiquitous in a galactic sense.


So the chances of finding advanced forms like us are slim to none in your opinion?

It makes you wonder what is so unique about our setup (and don't think I am going in an ID direction.).

If life were that common, you would naturally think there is a steady progression for advancement. Not a constant start and decay because the planet suddenly started becoming unhospitible. I also wonder how much time would have to pass for a planet to once be inhabited, and then become uninhabited because of enviromental changes. If you take the rough estimation of the age of the Universe and then add the slow progression of Evo to form those planets, and then have them become hospitible for basic forms of life. Throw in a little enviromental change, and suddenly no mas life of certain said planet. It is a very mind blowing idea at this point to me.

Even if you allow for a rapid rate for evo. The creation of those planets would have taken forever. I am sure most of those planets have not varied much in their solar location. SO what would have pushed them out of Hospitible range?

Just some thoughts as I try to wrap my mind around this concept.


There might be life on other planets or moons in the solar system. That's what the article I posted talks about. It is a long shot, but it's certainly not impossible. The gist of it, is that life probably requires an "active" planet; a place where chemicals are brought together with an energy source. The activity can be tidal, volcanic, etc.

That where the title of the article (and this thread) comes from: The hypothesis that life requires a "living" world to develop. If the hypothesis is correct, you won't find life on the moon, because it is tectonically and volcanically inert. You'd have better chances on Jupiter, or, for life more similar to the one to which we're used to, some of it's moons.

From your other comments, you seem to equate life with intelligent life, which is another thing entirely. Life on Earth has been present for about 3.5 billion years, but for most of that time, life only existed as unicellular organisms.

Intelligent life that can alter it's environment and develop technology might be extremely rare in the universe. While life itself could be relatively common, other conditions need to be present for a technological civilization to emerge and prosper.

The dinosaurs where around for some 300 millions years. Had they not been wiped out by a cataclysmic event, maybe mammals would never have had the chance to "take over" and evolve until we appeared.

Intelligent life with technology might also have a propensity for destroying itself. Be it through nuclear war, plague or destruction of it's environment, it might be that other civilizations have come and gone at other time periods. You can read a bunch or articles about that on the SETI website.

We have to keep in mind that we've been "advanced" for an extremely short period of time. We've had radio for about 110 years. So the first radio signals from Earth have travelled only 110 light years since then. In astronomical distances, we haven't reached the end of our back yard yet.

If there is another intelligent civilization in our galaxy, and it's living on the other side of it, it will take roughly 40,000 years for our signals to reach it. The same time will elapse for their answer to come back. It don't think we'll be having any meaningful conversations at that rate.

If there is only one advanced civilization per galaxy, then communication as we know it is pretty much out of the question. The distances involved are simply mind-bogglingly staggering.

Unless we figure out a way to go faster than light, or to "warp" spacetime to reduce distances... but we're leaving science for science fiction now.



WASHINGTON, DC (DPI) - History was changed forever yesterday when NASA received a transmission from an alien species. The brief message, addressed to "abuse@NASA.gov," read simply:

Humans --

Please discontinue sending stupid unsolicited transmissions and debris to us. We have received several metallic craft bearing objects, crude drawings, and disks which play noises when scratched with crystal-tipped needles. We don't know who "Bach" is, but tell him for us that he should consider another profession. Honestly, we receive thousands of unsolicited transmissions and craft from societies such as yourself to the point where they become a great nuisance, so discontinue this practice immediately or we will be forced to report you to your information provider or, more simply, blow up your stupid planet and all your stupid life-forms. Send your junk to the Gezor -- they have all the class and intelligence of stewed clazin. Regards,

Elinzoa Glppaducc
Information Processing Coordinator
The Shati-Makal

NASA immediately cancelled plans to send up a time capsule containing a CD of the Ricky Martin hit, "Livin' La Vida Loca", and a VHS copy of "Friends."


Actually I was equating life with possibility for advancement. Since the basic premise of evo is that all things adapt to their enviroment, and over time improve. I don't think that would be a tough thing to ask. I agree it is most likely rare to have what I am asking about. Since I would be an "ID" person I am merely trying to consider the possibilities and chances of life outside of ours (something most of us would not consider).

As for light going faster I have to say it is not that much science fiction. We know how to slow it down, speeding it up is only a little research away.


Anyone heard of the Drake Equation? It's a formula that calculates the number of planets that could harbour communicating civilizations in our galaxy. Basically, the equation is:

N = N* fp ne fl fi fc fL

N = The number of communicative civilizations
N* = The number of stars in the Milky Way (100 billion)
fp = The fraction of those stars with planets. (20%)
ne = The number of Earth-like worlds per planetary system (1)
fl = The fraction of those Earth-like planets where life actually develops (50%)
fi = The fraction of life sites where intelligence develops (50%)
fc = The fraction of communicative planets (those on which electromagnetic communications technology develops) (10%)
fL = the fraction of the planet's life during which the communicating civilizations survives (Earth is approx. 10 billion years-old, we have been communicating for 100 years and let's say our civilization survives another 9,900 years (yeah right), than fL would be 10,000 divided by 10 billion) (1/1,000,000)

While the equation is widely accepted, the values of the variables are the real source of discussion. Using the conservative values I have put in parenthesis, this would mean that there are at the moment 500 worlds in our galaxy that have the capabilities of interstellar communication. This is much less than the 10,000 originally estimated by the author of this equation, Frank Drake.

The point of all this is that when considering the incredible number of stars in our galaxy, an event that is statistically insignificant, like let's say development of intelligent life, is a certitude!

But unfourtunatley, considering the widenest of the Galaxy and our lack of intergalactic cruisers, the chance of meeting little green aliens are close to none for the moment.

So, my take on all of this: Life forms in our solar system, possibly; Intelligent life in our galaxy, of course; Chance of meeting an alien tomorrow, I wouldn't bet on it.