Extraterrestrial LifeExtraterrestrial LifeExtraterrestrial implies the UniverseBut we only KNOW about life on Earth (will use as “model”) Danger of “Earth Chauvinism”Objectives:Scientific PerspectiveUnderstand connection between Universe and LifeGive you tools to make your own judgmentsControversial Issues:EvolutionVisits by Aliens (UFO’s)Themes:Cosmic EvolutionThe Drake EquationContactThe Nearest StarsThe Nearest StarsGalaxy RotationSunLight YearTo Centerof GalaxyBarnard’s StarAlpha CentauriProximaCentauriBLalande 21185Wolf 359SiriusA + B25 Nearest Star SystemsLarger Structures• Milky Way Galaxy 100,000 (105) ly across• Local Group about 3 million (3 x 106) ly• Virgo Cluster about 30 million (3 x 107) lyaway• Most distant galaxies we can see are about13 billion (13 x 109) ly awayQuestions• How far from Earth are the astronauts in theShuttle?• How far have humans traveled (in light-timeunits)?• What fraction of the distance to the neareststar is that?• Are we likely to travel to another star in yourlifetimes?LifeFive Attributes of Life1. Composed of Organic Molecules (Carbon Based)2. Engages in Metabolism3. Reproduces4. Mutates (Evolves)5. Changes in Response to Environment (Sensitivity)Questions• Can you think of a counter-example to eachof these?• Something alive without these attributes?• Something not alive with these attributes?Alternative Approach to Definition of LifeBased on Ecological aspectClare Folsom (Onsager-Morowitz)“Life is that property of Matter that results in theCoupled Cycling of bioelements in AqueousSolution, ultimately driven by radiant energyto attain Maximum Complexity”Very general - but what does it mean?Gaia - Geochemical & Biological CyclesLife on Earth as “Organism” (James Lovelock)Requirements for LifeTo Make A: You Need:Virus < 17 ElementsBacteria ~ 17Human (Mammal) ~ 27Phosphorus (P) and Potassium (K) in shortest supplyAverage Human Being contains 6 × 1027atoms⇒ At least one atom of every stable element and someunstable (radioactive) elements (14C, 3H, 40K)⇒ Some atoms from every species that ever existedFacts from R. Davies U. Penn.Leaving aside rare elements, all life hassimilar composition: (All % by number of atoms)HCON Essential, most common PS Also essential Ca BonesAlso Fe (Iron) HemoglobinMg (Magnesium) ChlorophyllHuman Beings61%26%10.5%2.4%0.13%0.23%0.13%Bacteria63%29%6.4%1.4%0.12%0.06%ElementHydrogenOxygenCarbonNitrogenPhosphorusCalciumSulfurSymbolHOCNPCaSComposition of the Earth:Atmosphere21%78%(0.011% Carbon)Ocean~ 33%~67%Crust47%28%ElementOxygenSiliconNitrogenHydrogenQuestion: Which is most similar to that of life?Composition of life more likeComposition of Sun (Universe)% in Sun93%6.4%0.06%0.03%0.011%ElementHydrogenHeliumOxygenCarbonNitrogenSymbolHHeOCNAside from He, HOCNWhere did these elements come from?The Drake EquationDrake Equation: N = R* fp ne fl fi fc LN = number of communicable civilizations in our galaxyR = Rate at which stars formfp= Fraction of stars which have planetary systemsne= Number of planets, per planetary system, which are suitable for lifefl= Fraction of life bearing planets where intelligence developsfc= Fraction of planets with intelligent life which develop atechnological phase during which there is a capacity for and interest in interstellar communicationL = Average of lifetime of communicable civilizationsr = Average distance to nearest
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