Wednesday, 30 June 2010

• Precursors for life possible on Titan?

  
  Living in Buffalo NY, just down the street from CFI as a matter of fact, I got to help out/hang out with some of the student leaders there for the CFI Student Leader Conference that JT’s been blogging about.  While there (and at least a little inebriated) I was asked what I, as a chemist, thought about the recent flurry of news reports about ‘life on Titan’.  In case you’ve had your head buried under a rock, this http://www.ciclops.org/news/making_sense.php?id=6431&js=1 is what I'm talking about.   My response was along the lines of “Seems interesting.  But I’d put Europa higher on the list of probable places for life to develop.”   My reasoning was that Europa has a chemical composition thought to be similar to Earth (silica crust, iron core, water (ice) surface coating).   We know that life exists, and thus probably began, on Earth.  Even Earth’s extremophiles are evolved from an ancestor common to us.  So, we ‘know’ that life can begin in environments similar to Earth’s (or at least it’s pre-biotic environment) and exist in conditions favorable for liquid water.
  
  However, a new article (http://www.lpi.usra.edu/meetings/abscicon2010/pdf/5186.pdf ) seems to indicate, if the models of McKay et al (from the first link) are accurate, that we could have a potential source of organic molecules necessary for life (as we know it) on Titan.  This might very well alter the order of my list of which extraterrestrial bodies we are most likely to find life on.  Which is, of course, highly encouraging as the more places we can find life, the better our understanding of how it could have formed becomes.  And the more likely it is that we’ll be able to understand how ‘we’ came to be.
  
  For the non-chemists, what they've done is essentially replicate the atmosphere of Titan in a chember and the flooded it with UV (high energy) light.  When you get a sunburn you are chemically altering the structure of your outer layer of skin.  This is caused, as is skin cancer, by UV light which has enough energy to disrupt chemical bonds.   In chemistry there is a concept called "Activation Energy".  For a given reaction to occur this energy barrier must be overcome in order for the reaction to proceed.  Take the combustion of Magnesium in a flare for instance.   Once the activation energy has been reached magnesium rapidly combines with oxygen in order to form MgO (Magnesium Oxide).  It does this while releasing large amounts of energy.  So why doesn't any magnesium exposed to air just instantly combust?  It is because the amount of ambient energy available at ‘normal’ temperatures doesn’t donate enough energy to overcome the activation energy required for MgO to form.   But the amount of energy released by the MgO is more than needs to be added to overcome the activation energy.  So what’s happening here?   Well, it’s thermodynamics at work.  Chemical compounds ‘like’ to form at the lowest energy state possible.  The bond energy of MgO is lower than that of just Mg or oxygen gas.   So, when you combine those two compounds and form MgO, you also form heat, the amount of which is equal (assuming perfect conditions) to the differences in energy levels between Mg and O2 and the product, MgO. 

  Okay. . . . So what does that mean?  Well, without UV light it means that the chemicals in Titan’s atmosphere could potentially remain unreacted forever, but if there is enough UV light hitting the cloud layer on Titan where these chemicals exist. . . Then they could potentially react to form organic compounds that we suspect are precursors for life. . .  So it means some potentially really really cool things.  As well as more work for the scientific community.

  
  

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