In another decade or so, we should have space-based telescopes actively looking for life around other stars by studying the atmospheres of exoplanets. In the beginning, it will make sense to look for bio-chemistries similar to our own. This isn’t some kind of species chauvinism but simple realism. We know more about how life works on Earth than it might in far more extreme environments, so we’ll turn first to Earth analogues, seeking the bio-signatures of carbon-based metabolisms on worlds with liquid water.
But as we explore our own Solar System, the situation will continue to evolve. If life exists on Enceladus, or Ceres, or in some bizarre Kuiper Belt ecosystem, it’s not going to be operating on the same principles as life here on Earth. These aren’t Earth analogues, and moreover, they are places for which we have the possibility of lander and rover exploration within the forseeable future. We’ll want to widen our range so we don’t overlook a form of life that isn’t immediately recognizable.
A new report from the National Research Council comes to the same conclusion, underlining how important it is that we be open to life forms other than those we can extrapolate from our own environment. Thus this clip:
“…no discovery that we can make in our exploration of the solar system would have greater impact on our view of our position in the cosmos, or be more inspiring, than the discovery of an alien life form, even a primitive one. At the same time, it is clear that nothing would be more tragic in the American exploration of space than to encounter alien life without recognizing it.”
How to recognize it? One way to prepare is to continue to explore extreme environments on our own planet, where we’ve already found life in deep oceanic vents and deserts as hostile as the Atacama. How life adapts to places where resources are incredibly scarce may tell us much about how living things might have adapted to hostile conditions below, for example, the surface of Mars.
But the report goes further, stressing that we need to move beyond the idea of water as crucial for life. Could there be places on Mars more suited to life than those where water once flowed? For that matter, what about different biochemistries altogether? According to the study, liquids like ammonia might serve as bio-solvents for living things far different than any we’ve so far imagined. A world like Titan, which the report pegs as the Solar System’s most likely home for what it calls ‘weird life,’ may well have capacious mixtures of liquid water and ammonia in its interior.
What we find in the Solar System should give us an idea how flexible we can be in our conception of life’s range around other stars. It may be that our early exoplanet work will routinely find bio-signatures in the spectra of terrestrial-type worlds, keeping us so busy analyzing the results that other environments are pushed to the back burner. But my guess is we’ll eventually find puzzling data that indicates life has taken unusual directions in far more exotic places, a finding that should be at once inspiring and humbling.
The report is The Limits of Organic Life in Planetary Systems, published by National Academies Press and available here.
Perhaps also consider Io and Venus as abodes for weird life based on some other fluid; vast energy flows on both worlds.
It is the biologists’ fondest dream to find life elsewhere. This would double our sample and finally let us establish which requirements for life are universal and which are parochial. It is also the biologists’ worst nightmare that we may destroy extraterrestrial life before we recognize it as such. We have done that already inadvertently with exotic life on earth, and some scientists are arguing that the Vikings did the same on Mars.
I wrote a brief essay on this issue here: You Only Find What You’re Looking For
This is precisely why I think all these clever chemical tests for life on other planets (e.g. what the Viking landers did) are futile. Assumptions of the chemistry of other life forms is going to get you nowhere when your sample size of planets supporting biospheres is one (unless the universe is particularly unimaginative when it comes to biochemistry). Send microscopes instead!
(Of course, getting a microscope to survive launch and landing is a whole technical issue in itself…)
Is it possible to get an idea of what a planet should be like chemically based soley on astronomical and geological models, and then look for deviations that might be caused by (some kind of) life? Or is there too much possible variation? Just trying to think of a generic way of spotting anomalies.
NS, I’m sure others will have comments, but one thing to look at is the spectroscopic data, once we’re able to pull them out of the starshine for an individual exoplanet. There the possibility of picking up biomarkers is significant, looking for combinations like methane and oxygen in proportions that suggest living organisms. Here are two previous posts that may be useful:
https://centauri-dreams.org/?p=1320
https://centauri-dreams.org/?p=821
Of course, it gets much trickier when we’re talking about exotic forms of life — there, we run the risk of picking up their signature but not being able to identify it. I think the NRC study is right on about this.
Paul, I understand that your post for today is number 1000 for Centauri Dreams. Congratulations and best wishes for your continued success in publishing such a fascinating and informative web log.
Kermit
Many thanks, Kermit. Much appreciated!
To the Administrator, thanks. The links are along the lines of what I was thinking. But if scientists could determine (say) based on composition of stellar dust clouds, planet sizes and type (rocky, gas giant), distances from the host star etc. what primordial planetary atmospheres should look like, then any deviations from that would be worth investigating. That is, work “forward” from astronomy and geology rather than “backward” from known life.
NS, a good idea, but the trick is that there are so many variables that we still don’t understand. As we’ll see tomorrow, for example, we keep finding planets that don’t quite fit our model of planetary formation, suggesting we’re a long way from getting a consistent model for every kind of star. One day we’ll have a large enough sample to spot the kind of anomalies you’re talking about, though until then we’ll probably have to rely on more direct spectroscopic observations when trying to detect signs of life.
David Grinspoon has advocated life on Venus, both in its
clouds and under its surface.
http://www.space.com/scienceastronomy/060221_venus_life.html
If life can exist on Venus or Io – or even in the center of
stars as some have seriously suggested – then perhaps “dead”
worlds are the exception, not the rule, and our Sol system is
an exception in a galaxy teeming with all kinds of life.
A case for carbon and water.
All the same, the fundamental laws of physics as well as matter (the elements) as we know them are omnipresent. Therefore life will have to ‘obey’ the same basic rules anywhere. Hence, I think that it IS possible to make some, at least probable, statements about life in the universe (well, the MW galaxy to begin with):
– it is highly likely that any biological life will be based on carbon (C), since it is the only element capable of building the complex molecules necessary for life;
– it is highly likely that any biological life will be based on water (H2O), because of its unique characteristics as a transport and process fluid.
– oxygen? Probably commonly used, because it comes in so handy for releasing energy, especially in combination with C, but maybe not always necessary.
It is often being said that we have only one sample, Earth. Only partly true, because at the same time we have countless samples of lifeforms on it, all based on carbon and water, most on oxygen as well.
This can of course be attributed to common ancestry but I think that is to simple. In my knowledge, during its entire existence and particularly during its first 3 billion years of microbiological experimenting, the earth, though all its time and circumstances, produced only carbon and water based life, and nothing else. I find that a pretty strong argument for those two key players.
All in all, the searching for biomarkers as defined, is not such a bad idea at all.
Maybe I should have added one thing; my previous posting may seem limiting, but is not so: with carbon based biochemistry the possibilities (i.e. possible number of organic molecules) are still endless.
Hi Ron
That paper that Paul discusses in the post is well worth a read – some of the possibilities are mind-blowing. The creatures from Hal Clement’s various novels have always been a favourite of mine, and it made me smile that sulphuric acid is a possible biosolvent according to the paper – the creatures of Tenebra being an example of such unlikely seeming life. Venus might harbour the nearest examples of such in her clouds.
The Cyborg Astrobiologist: Porting from a wearable computer to the Astrobiology Phone-cam
Authors: Alexandra Bartolo, Patrick C. McGuire, Kenneth P. Camilleri, Christopher Spiteri, Jonathan C. Borg, Philip J. Farrugia, Jens Ormo, Javier Gomez-Elvira, Jose Antonio Rodriguez-Manfredi, Enrique Diaz-Martinez, Helge Ritter, Robert Haschke, Markus Oesker, Joerg Ontrup
(Submitted on 5 Jul 2007)
Abstract: We have used a simple camera phone to significantly improve an `exploration system’ for astrobiology and geology. This camera phone will make it much easier to develop and test computer-vision algorithms for future planetary exploration. We envision that the `Astrobiology Phone-cam’ exploration system can be fruitfully used in other problem domains as well.
Comments: 15 pages, 4 figures, accepted for publication in the International Journal of Astrobiology
Subjects: Computer Vision and Pattern Recognition (cs.CV); Astrophysics (astro-ph); Artificial Intelligence (cs.AI); Computational Engineering, Finance, and Science (cs.CE); Human-Computer Interaction (cs.HC); Networking and Internet Architecture (cs.NI); Robotics (cs.RO); Software Engineering (cs.SE)
Cite as: arXiv:0707.0808v1 [cs.CV]
Submission history
From: Patrick C. McGuire [view email]
[v1] Thu, 5 Jul 2007 15:19:37 GMT (650kb,D)
http://arxiv.org/abs/0707.0808
Biology in Science Fiction
http://sciencefictionbiology.blogspot.com
By Ken Newquist
Those who think aliens with wrinkled noses are an infuriatingly lazy approach to depicting the potential diversity of life in the universe will find a welcome home at Biology in Science Fiction.
The blog chronicles the intersections of speculative fiction and the life sciences, with recent posts invoking William Gibson in a conversation about how memories are stored in the brain, running down recommended summer reading from Science magazine and lamenting the lack of respect biologists get in the genre.
Updates are posted daily and feature a rich mix of news, books, movies, commentary and interviews. The site includes links to its most popular posts—such as the genetics of Heroes—as well links to various SF biology resources around the web. The combination makes the site perfect for those who like a little more science in their fiction, as well as biology fans seeking to keep up with the speculative aspects of their field.
http://www.scifi.com/sfw/sites/sfw16160.html
I’m a little late to this party, but, as an armchair exobiology fan, I would like to add that I would guess, based on evolution of life on our sample of one planet, that life most likey is less dependent on the chemical composition (as I understand it, ammonia offers possible water protein analogs and is also a good solvent, and there are other more exotic possibilities) than it is on the medium of its creation.
By this I mean that it seems that, for example, organic compounds form in the most, to us, hostile environments possible i.e. in the kuiper belts and Oort clouds., very likely as a result of disk accretion bringing these components together with time. Given that any planetry body that then falls within one of the ranges of so-called habitility zones (it would be further out for ammonia based life, for instance), and the constant mixing and reacting and shaping of molecules would then very likely produce the first example of what we would call life.
I think that looking at the extremophiles as examples of where life could originate might be somewhat misleading, however. It is very likely that life needed a solvent to originate, and that the first examples were anaerobic (which is exotic to us as a species today), but I think it is otherwise likely that extremophiles adapted to fill the niche environments, and did not originate there.
Given these possibilities, life might even evolve on a place like Titan, using liquid methane as a nuturing solution. It would obviously react far more slowly than life on earth would, and due to the extreme cold might have only produced single cell organisms until now. Life might just as easily have started underneath the ice of Europa, Enceladeus, Charon and others.
However, I personally doubt it. I would guess that life also needs an abundant supply of energy (or energy gradient to the ambient energy level) that simply makes the chances of life starting in cryovolcanoes very unlikey. I also think that a certain stability might be needed, amongst the chaos, that would make life on gas giants also unlikely.
In other words, I am, sadly, of the opinion that life is more likey to be similar to us than we could guess, but alos fairly abundant, given that even moons of a Jovian analog in a habitable zone might produce life.
Claim of Martian Life Called ‘Bogus’
http://bcast1.imaginova.com/t?r=2&ctl=1AF49:4A48D
The search for life out side our planet will be very difficult, and by the time it has succeeded, will very likely be embarrassing for us as a species. Our ability to recognize such unfamiliar life is infantile at best. Unless on our first stops out there harbor life forms similar enough to recognize and at the same time different enough to expand our knowledge base to include a few of the myriad of other possibilities, we will most likely conclude there is no life on many many worlds we may visit. The likelihood of life as we know it here is really quite remote, even on worlds that have a relatively similar makeup. For us to postulate correctly the types of life we will come across is flat out statistically impossible. The proof of that is in the discoveries made in the 30 years since we launched Voyager. We have discovered many different life forms that give us real pause as to what we should be looking for even on a planet as similar to ours as Mars. We will eventually, after many stops, realize that there was life on several previously explored systems and we failed to recognize it. The fact that we expect life to take the same path as it did on earth is just another facet of our limited knowledge that even further limits our imagination and all that is fueled by a built in arrogance that is not necessarily our fault (we are after all the smartest species we know). I have high hopes for our further exploration of the universe, but I believe there will be many disappointments in that process.
Could Life On Earth Have Come From Ceres
Moffett Field CA (SPX) Mar 06, 2009 – Astrobiologists hope to find life elsewhere in the universe, or possibly even in our own cosmic neighborhood, the solar system. Their efforts are usually concentrated on worlds such as the planet Mars, or icy moons like Europa. However, there are other, less conventional locations in the solar system where scientists think life may be found. … more
http://www.spacedaily.com/reports/Could_Life_On_Earth_Have_Come_From_Ceres_999.html