Thursday, September 30, 2010

Finding Life in Unexpected Places

I wanted to start off with a few articles here and here that I found referencing a certain planet named Gliese581g in the Gliese581 system, nicknamed the "Goldilocks" planet, and I'm sure you can imagine why:

One of the articles refers to a laser signal coming from its solar system, while the other claims that there is no doubt that this planet has water on it, possibly an atmosphere, and is just the right distance away from its star to harbor a stable, reasonable temperature.

Of course, as it points out, we're on a fantastic delay when it comes to communicating with the distant 20-light-year path to its star, taking around forty years to actually get a response, and a lot can happen in forty years.

What I wanted to do in this blog post, however, is talk about the limits of life. Is water truly a necessity as these articles seem to claim? What about ammonia? I found a National Academies of Science report on The Limits of Organic Life in Planetary Systems that took this idea and asked a few important questions. Here are some I believe are more relevant to the topic at hand:

"What life forms are possible, still based on carbon, but not functioning in water?"

"Can mineral systems be identified that interact in interesting ways with organic compounds in nonaqueous systems?"

"Can asymmetric induction, and spontaneous resolution that leads to the homochirality assumed to be necessary for life, be achieved in nonaqueous solvents, especially those found on solar system bodies other than Earth?"

"Can a system capable of Darwinian evolution be demonstrated in the laboratory using nonstandard monomers and/or biopolymers in nonaqueous environments?" (preface. x)

So, there's the question at hand: is water all that necessary?

Here's what the report says about why water is just so great:

"Many specific properties of water are cited to make the case that water is an ideal biosolvent uniquely suited to support life: Frozen water floats. Water is an excellent solvent for salts. Water is liquid over a broad range of temperature. Indeed, the concept of a habitable zone, a region around a star where life is presumed to be possible, largely posits a region in which a planet’s surface or subsurface might support liquid water" (69).

So, let's take a look at ammonia, since that's the one we were talking about last class.

Ammonia stays liquid throughout a large range of temperatures, 195-240 K, and it's reasonably good at being a solvent. It's also abundant in the cosmos. However, something strikes it down when compared with our own living situation:

"The increased strength of the dominant base in ammonia,as well as the corresponding enhanced aggressivity of ammonia as a nucleophile, implies that ammonia would not support the metabolic chemistry found in terran life" (72).

So, as I look through some of the other profiles for other biosolvents (things like carbon dioxide clouds and sulfuric acid), I've noticed how different the workings of a non-water planet might be, even if it may be able to sustain "life" as we don't know it. This leads me to believe that the likelihood of finding intelligent life--according to the current definition--is much slimmer in these environments, since many of their missing aspects have contributed greatly to our evolution.

One of the more interesting topics is whether evolution is a necessity, or if a constantly changing environment may continuously create new and different types of life. While this may hinder intelligent life, it might have untold positive effects elsewhere.

"The unity of biochemistry among all Earth’s organisms emphasizes the ability of organisms to interact with other organisms to form coevolving communities, to acquire and transmit new genes, to use old genes in new ways, to exploit new habitats, and, most important, to evolve mechanisms to help to control their own evolution. Those characteristics would probably be present in extraterrestrial life even if it had a separate origin and a unified biochemistry different from that of Earth life" (8).

So, maybe not necessarily traditional evolution as we know it, but there are similarities that would make life on Earth and life on a non-water-based planet--if it is filled with life--very similar in terms of what we consider biochemical progress Although from what I've read, I can't imagine it would be the intense, laborious evolution that would breed what we would consider intelligent life.

Water is just too convenient in too many ways.


  1. Hi Nik,
    Thank you for looking into the issue of ammonia as the potential liquid medium for life. It does seem that the nitrogen in ammonia makes life hard for carbon-based polymers; I think in class we talked about the problems of using Silicon or another similar element as the skeleton for life, and came to the conclusion that the bond energies were just too weak.
    I'm not sure that there's an alternative to sequential evolutionary steps--a model in which abiotic chemistry spins off a succession of one-off life forms is not a recipe to get anything complex (of course, it might actually have happened that way on our planet, before life took hold for good). It's really hard to build a radio telescope if you're not multicellular and specialized in some way.

  2. Oh, also, rereading the article on the "laser signal" was encouraging, as the guy seems not to be totally loony...

  3. Hey Nik,

    I was looking at a site that relates to your post ( which adds a few more pros of ammonia as a solvent (as used by organic chemists), but ultimately decides that one of the major problems is its inability to pack hydrophobic regions together, since its hydrogen bonding is weaker than that of water.
    Yet again, we determine that ammonia is just not as convenient as water.