Searching for Life in Our Solar System: Chapter 6 Introduction Environmental requirements of life –Elements of the periodic table –Energy for metabolism –Liquid solution for living systems Concept of “habitability zones” Passing the baton to Professor Geller

Searching for Life in Our Solar System Where would you go to search for life in our solar system? Systematically, how would you prioritize the criteria to use in the process of searching? For each criteria, for what would you specifically look? What methodologies would you use? How confident/uncertain would you be relative to proving or disproving “life signs”?

Elements of the Periodic Table

Elements of the Solar System Source and abundance of H (hydrogen) and He (helium) due to Big Bang (conversion of energy into mass) –98% of solar mass Source of all “other” elements was the interior of stars (chemical reactions among elements and subatomic particles) –Rare relative to H and He Planetesimals everywhere should contain elements needed for life

Elements of the Solar System: Role in Living Systems 25 of 92 natural elements are known to be essential to life on Earth 4 of the above make up 96% –Carbon (C), Oxygen (O), Hydrogen (H) and Nitrogen (N) Remainder (4%) are mostly Phosphorus (P), Sulfur (S), calcium (Ca) and Potassium (K) Compare to solar abundance and discuss relative to evolution of biochemistry in origin of life

Energy for Metabolism Introduction Sunlight and photochemical energy –Energy decreases with square of distance from source (e.g., Sun) –Example: leaf on Earth versus leaf twice as far out from Earth (1/4 as much energy) –Example: 10 times further out, energy would be 1/10 2 or 0.01times as much

Energy for Metabolism Chemical energy: ongoing chemical reactions that can supply energy for metabolism Example: FeS + H 2 S FeS 2 + H 2 + free energy Requirements –Atmosphere with mixing –Liquid medium with mixing –Solid-liquid reactor/mixing

Energy for Metabolism Internal sources of heat for mixing –Moon and Mercury (?) –Earth, Mars and Venus –Jovian planets (surface lacks solid surface) –Jovian moons (Io, Europa) Atmospheric mixing –Jovian planets (chemical and electrical energy) Conclusions –Our solar system (internal geology and liquid medium) –Other systems?

Liquid Solution for Living Systems Introduction –Life on Earth in water….~4 BYA –First 3 BY of life in water alone –All life tied to watery medium (plants, animals and microbes) –“Habitability” of Earth f [water] Simplicity and complexity of the nature of the water molecule –Deceptively simple in structure –Exquisite in function

Water and Its Properties: Elemental Composition Elemental composition of H 2 O –Hydrogen is the most abundant element in universe –Oxygen is the 5 th most abundant element Conclusion: H 2 O is probably common throughout the Universe

Water and Its Properties: Polarity Composition and structure: a polar molecule Features –Attraction is electrical –Hydrogen bonding among two molecules of H 2 O Exquisite properties of H 2 O arise from chemical attractions because it is a polar molecule: emergent properties O H+H+ H+H+ -

Water and Its Properties: Liquid State Water is liquid over broad range of temperatures 0 o C to 100 o C Other CompoundChemical FormulaFreezeVaporRange ( o C) ( o C) ( o C) Water H 2 O Ammonia NH Methane CH Ethane C 2 H

Water and Its Properties: Liquid State Significance of broad range for water to exist as a liquid –Temperatures on many planetary bodies must have been or are within range so water exists as a liquid –Water in a liquid state is not too cold to slow reactions and bonding of carbon and not too hot to break bonds

Water and Its Properties: Cohesion of H 2 O Molecules Cohesion: H 2 O molecules are “sticky” Liquid: fragile hydrogen bonds (5% of covalent) Each bond last 1x seconds Constant formation and breakage of bonds: any moment a substantial number of H 2 O molecules are bonded to neighbors Consequence: more structure than other liquids

Water and Its Properties: Water Moderates Temperatures on Earth Water stabilizes temperatures by absorbing heat from air Mechanism –Specific heat (SH): usually high SH for H 2 O –Change temperature less when absorbing or losing heat (e.g., metal pot with water) –Due to hydrogen bonding Relevance –Absorption of heat in the summer by ocean and re-release of heat (i.e., evening, winter) –Evaporative cooling Define: vaporization and loss of heat Evaporative cooling of tropical systems Evaporative cooling of your body

Water and Its Properties: Freezing of Oceans and Lakes Water is unusual in that H 2 O is less dense as a solid than a liquid (it floats) Mechanism –H 2 O expands when it solidifies –Due to hydrogen bonding Consequence –Ponds, lakes and ocean freeze from the top down

Water and Its Properties: Solvent of Life Water is versatile solvent, due to its polarity and dissociation H 2 O H + + OH - –In pure water, 1 molecule in every 554 million is dissociated (10 -7 molar concentration)…pH scale –Statistically very rare BUT exceedingly important in chemistry of life (e.g., proteins, macromolecules) H + and OH - are very reactive and affect much of the chemistry of living systems on Earth (e.g., membranes)