Searching for Life As We Don't Know It
Written by Nancy Atkinson
When discussing the possibility of finding life on other worlds, we usually add the phrase "life – as we know it." But we've been surprised at exotic forms of life even on our own world and we need figure out how life might evolve elsewhere with foreign biochemistry in alien environments. Scientists at a new interdisciplinary research institute in Austria are working to understand exotic life and how we might find it.
Traditionally, planets that might sustain life are looked for in the ‘habitable zone’, the region around a star in which Earth-like planets with carbon dioxide, water vapor and nitrogen atmospheres could maintain liquid water on their surfaces. Consequently, scientists have been looking for biomarkers produced by extraterrestrial life with metabolisms resembling the terrestrial ones, where water is used as a solvent and the building blocks of life, amino acids, are based on carbon and oxygen. However, these may not be the only conditions under which life could evolve.
The University of Vienna established a research group for Alternative Solvents as a Basis for Life Supporting Zones in (Exo-)Planetary Systems in May 2009, under the leadership of Maria Firneis.
“It is time to make a radical change in our present geocentric mindset for life as we know it on Earth,” said Dr. Johannes Leitner, from the research group. “Even though this is the only kind of life we know, it cannot be ruled out that life forms have evolved somewhere that neither rely on water nor on a carbon and oxygen based metabolism.”
One requirement for a life-supporting solvent is that it remains liquid over a large temperature range. Water is liquid between 0°C and 100°C, but other solvents exist which are liquid over more than 200 °C. Such a solvent would allow an ocean on a planet closer to the central star. The reverse scenario is also possible. A liquid ocean of ammonia could exist much further from a star. Furthermore, sulphuric acid can be found within the cloud layers of Venus and we now know that lakes of methane/ethane cover parts of the surface of the Saturnian satellite Titan.
Consequently, the discussion on potential life and the best strategies for its detection is ongoing and not only limited to exoplanets and habitable zones. The newly established research group at the University of Vienna, together with international collaborators, will investigate the properties of a range of solvents other than water, including their abundance in space, thermal and biochemical characteristics as well as their ability to support the origin and evolution of life supporting metabolisms.
“Even though most exoplanets we have discovered so far around stars are probably gas planets, it is a matter of time until smaller, Earth-size exoplanets are discovered,” said Leitner.
The research group discussed their initial investigations at the European Planetary Science Conference in Potsdam, Germany.
Source: Europlanet
Filed under: Astrobiology
Tags: AstrobiologyRelated stories on Universe Today
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September 17th, 2009 at 7:51 pm
I read somewhere (I don't remember where) that water is really the best choice for a life-sustaining solvent due to the fact it's one of the few substances that's lighter as a solid than as a liquid (which helps ice float). If, say, it gets colder (relatively speaking) and a methane lake freezes, the "ice" would tend to sink, probably suffocating any marine life at the bottom of the lake. Also, this would expose more liquid to freezing temperatures above, causing more and more of the body of liquid to freeze until the whole thing is rock solid. On Earth, water doesn't have that problem as the ice stays on top and "insulates" the liquid below from freezing during the winder months.
September 17th, 2009 at 7:54 pm
Oops, the last two words of my previous post should read "winter months". At least I didn't misspell "shot" like someone else famously did a couple of months ago (for those that don't know/remember, note that the "o" and "i" keys are very close together on a standard US keyboard)
September 17th, 2009 at 9:57 pm
Today's XKCD seems relevant to this.
http://xkcd.com/638/
September 18th, 2009 at 4:55 am
This is the type of research that as a layman you have only to shrug your shoulder at. It's quite impossible to estimate its potential impact.
For one, detection of biospheres will probably rely on identifying thermodynamically unstable situations and distinguish them from geological processes, such as ozone on Earth and methane on Mars (Earth) as opposed to methane on Titan.
For another, the idea of a likely habitable zone is merely (IMHO) to focus investigations and enable estimates. It will be very hard to place probabilities for actual habitability since there are so many pathways. At least until we have more examples of biospheres.
IIRC investigators for Phoenix took a more practical approach to habitability, placing bayesian estimates on contributing factors in a Drake equation type model.
[For one example of funny pathways, the recent discovery of high temperature abiotically synthesis of pyrroles on salts comes to mind.
Pyrroles are constituents of hemes and are made higher up in the metabolic hierarchy, just after the citric acid cycle. But they look for all this layman can tell as a potential substitute for sugars in nucleosides, much the same planar geometry albeit a nitrogen has been substituted for oxygen. They do interfere with DNA, but I'm not sure about the mechanism yet. (Damn paywalls!)
Sugars seems to be rare abiotically, which was a problem for the RNA world model.
Now at least two nucleosides have been shown abiotically synthesized in toto from linear fragments. It looks schematically very like the biologic synthesis of pyrroles from the same. (Making you wonder how this pathway were missed for so long.) Perhaps instead pyrroles were the previous backbone in an RNA analog, which would explain later metabolic incorporation and exaptation for rather complicated heme.
Then you would need to add salt deposits and heat vents in the pathway to us.]
September 18th, 2009 at 6:09 am
We need to look at the possibility of silicon based life, or life that uses ammonia as a solvent. Hydrogen peroxide might be something to investigate as well.
September 18th, 2009 at 6:57 am
And now, the Rock People of Epsilon Zeta 5 say: "Hmmm…perhaps these carbon-based life forms are not so ignorant after all."
September 18th, 2009 at 7:14 am
The approach described in the article is rather interesting.
The various attempts to define life, and especially to characterize what distinguishes life from the inanimate objects, appear — at least for me, not being a biologist — only descriptive or accidental, i.e. as in philosophy "relating to or denoting properties that are not essential to a thing's nature". Without wanting to insult anybody — it looks like there is no sound foundation of biology regarding this basic concept. This situation is in contrast to physics with the basic concepts of length, time, mass etc.
Hmm … or is "life" not a basic concept of the science of biology? Does anybody know? And if not, then why?
At least as long as there is no essential definition of life, researchers should look into many directions.
September 18th, 2009 at 10:11 am
Time to brush up on cryogenic fluids methinks… because now I've got some questionszuh….
Q: What elements remain fluidic at these temperatures?
Q: Which of those are effected by magnetic fields?
Q: Which of those elements are are easily ionized?
Q: Which of them are lo-temp superconductors?
Q: What implications might superconducting properties have for cryogenic lifeforms?
Coherent cold plasmas anyone?
September 18th, 2009 at 10:26 am
Q: What kinds of crystals might be formed from elements with superconducting properties?
Q: Are superconducting elements good antenna's?
Q: Does this imply the possibility of light speed synapse for vast (Planetary scale) organisms?
Recent temp. maps from LCROSS have found a perfect laboratory for answering such questions in lunar pole craters
September 18th, 2009 at 11:39 am
It joins the vast family of other such concepts, such as mind (no definition) or species (at least 26 different definitions). Or similar fuzzy concepts outside biology, such as "financial capital". Yet one can use it.
There is one sound definition, the problem is that it doesn't tell you much about outcomes.
Life as we know it is a process, the process of evolution on biological populations. It is likely to be the most probable form of biology, as static eternally living life forms or non-genetic modifiable communities evidently are out-competed. It is a local Earth variant on the Fermi question, "where are they?".
Evolution can of course be soundly defined based on observation, for example:
"Evolution is a process that results in heritable changes in a population spread over many generations."
Note the observationally based similarity to for example a definition of gravitation:
"Gravitation is a process that results in accelerations in a test mass caused by another mass."
Some biologists, especially those who wants to incorporate virus in a natural way with the rest of biology, has proposed to elaborate a definition of life based on this. Beyond, somewhat redundantly, being the process itself. Or more specifically being a property of the participating populations.
But as a derived property of individual biological entities as well, for example:
"An organism is the unit element of a continuous lineage with an individual evolutionary history."
So _we_ may be alive too, not just our species.
Whatever you choose, there is a problem here: biology as a product of evolution is a highly contingent outcome. How do you recognize a biosphere?
Contrasted to this you have "the NASA definition" optimized to find and recognize biological entities, roughly "replication and metabolism". Or as I noted above, signatures of biospheres.
Of course, looking for either evolutionary processes (or replication) or metabolism are inclusive. Then genetic algorithm software (or crystals) and recycled cars are "life".
Specifying biochemistry works to resolve that ambiguity, it seems to me.
[But also using both evolution and metabolism at the same time. Then replicating robots would be recognized as life, which is also fine with me.]
September 18th, 2009 at 11:54 am
duh! "Then replicating robots would be recognized as life" – Then sloppily self-replicating robots would be recognized as life.
September 18th, 2009 at 2:50 pm
"Only that world can appear to us which we mentally perceive."
"Man's experience is the logical outcome of his inner vision; his horizon is limited to the confines of his own consciousness."
SOM
September 18th, 2009 at 3:08 pm
UNBIND your mind, there is NO time! To lick your stamps! And paste them in! Discorporate and we'll begin!
Ahemm.. Spraking of speaking with aliens! HeyNOW!
September 18th, 2009 at 6:28 pm
Torbjorn Larsson OM: duh! "Then replicating robots would be recognized as life" – Then sloppily self-replicating robots would be recognized as life.
Of course, I have read a lot in books, newsletters, and on the web about the various approaches to defining life. I have not been surprised, that there are at least two camps of biologists (and lay people): (a) one camp thinking, that there is a clear cut distinction between living beings and robots or computers or computer programs or something like that; (b) a second camp thinking, if it looks the same at the surface, then it is the same, i.e. certain robots (etc.) are or will be (considered as) animate.
I'm a member of the first camp. If a very sophisticated *something* comes along, and somebody claims this something to *be* a living being, then, I think, we will, by looking inside, be able to recognize, that the claim is not justified. This is difficult or impossible, when observing — and only observing — a distant planet. Even if we see a lot of pertinent biomarkers, there may be no life, but something different.
September 19th, 2009 at 6:14 am
I tend to agree with Torbjorn Larsson. This is not empirical territory exaclty. It may well be the universe permits a wide range of complexity which permits self-replicating structures of considerable diversity. We might be fortunate if we can study any of this sort of thing.
To really understand this issue we ever more data on extrasolar systems, such as imaging terrestrial planets. To really have some idea of what complex structures might exist there we would need to plant probes and robots on planetary surfaces around other stars. My book "Can Star Systems be Explored?" addresses some issues with this problem.
LC