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Life: What Do We Expect?

Life: What Do We Expect?. George Lebo 24 October 2012 AST 2037. 1. Life Needs. Need energy source and reproductive code Likely energy sources: light, chemical energy Reproductive code: likely chemical, and requires complex molecules/chains

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Life: What Do We Expect?

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  1. Life: What Do We Expect? George Lebo 24 October 2012 AST 2037 1

  2. Life Needs • Need energy source and reproductive code • Likely energy sources: light, chemical energy • Reproductive code: likely chemical, and requires complex molecules/chains • A little weaker: May have a preference for liquid phase? • Probably need a powerful solvent 2

  3. Complex Molecules • Abundant elements in the Universe: • H (can only bond with one electron) • He (noble gas) • C • O • Ne (noble gas) • N • Si • Fe 3

  4. Other Options? • Oxygen only makes two stable molecules with hydrogen: water (H2O) and hydrogen peroxide (H2O2) • Nitrogen only makes two also: ammonia (NH3) and hydrazine (N2H2) • Fe also relatively limited in its bonding • Carbon makes a nearly endless number of molecules/isomers with H • Si also makes lots of molecules too 4

  5. Si vs. C • Both C and Si can make complex chains and diverse molecules • But … C-C bond is about as strong as C-H and C-O bonds • Si-Si bond is about ½ as strong as Si-H and Si-O bond • Carbon can make long C-C-C chains • Silicon unstable for long chains; Si-O can form chains (silicone), but they don’t like to attach other elements (often used as lubricants) • If oxygen present, Si forms SiO2 preferentially (while many C molecules about equal – CH4, CO, CO2, alcohol, sugars, etc.) • SiO2 (quartz/sand) is a solid at most reasonable temperatures for complex chemical reactions; only soluble in hydroflouric acid 5

  6. Si Life? • Develops elsewhere, comes to Earth • “Skin” must be resistant to oxidation  SiO2 (rock) “armor” • Digestion might produce silane SiH4 (analogy to CH4 methane) • Belch silane into oxygen atmosphere  preference for Si-O bonds creates rapid chemical reaction in the gas  ignites into flame • What would that look like? • Rock for skin  impervious • Breathes fire 6

  7. Solvent Issues • Want broad temperature range for liquid state • Common molecules • High thermal capacity • Can “move” heat around for temperature regulation (important for complex life – probably …) • High heat of vaporization • Evaporative cooling • Lower heat of vaporization means less efficient cooling 7

  8. Possible Solvents • H2O is most common molecule in the Universe, after H2 • Other contenders: • Ammonia • Methyl alcohol • Ammonia has only ~45C temp range as liquid • Methyl alcohol has OK temp range but ~1/2 heat capacity of water • Water has about x2 higher heat of vaporization • These others can work (esp., liquid at lower temps than water); but, we expect water to be better 8

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