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Extraterrestrial Life
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Extraterrestrial 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 judgments
Controversial Issues:EvolutionVisits by Aliens (UFO’s)
Themes:Cosmic EvolutionThe Drake EquationContact
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The Cosmic Context
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The Nearest Stars
Galaxy RotationSun
Light Year
To Cen
ter
of Gala
xy
Barnard’s StarAlpha Centauri
ProximaCentauriB
Lalande 21185
Wolf 359
SiriusA + B
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25 Nearest Star Systems
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Larger 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) ly• Most distant galaxies we can see are about
13 billion (13 x 109) ly away
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The Milky Way
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Our Location in the Milky Way
25000 light years
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The Local Group2 million light years
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Central Part of Virgo Cluster
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The Hubble Deep Field
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Try this Link
http://www.atlasoftheuniverse.com/index.html
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Questions
• How far from Earth are the astronauts in theSpace Station?
• 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?
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Life
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Five Attributes of Life1. Composed of Organic Molecules (Carbon Based)
2. Engages in Metabolism
3. Reproduces
4. Mutates (Evolves)
5. Changes in Response to Environment (Sensitivity)
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Questions
• Can you think of a counter-example to eachof these?
• Something alive without these attributes?• Something not alive with these attributes?
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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)
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Requirements for LifeTo Make a: You Need:
Virus < 17 ElementsBacteria ~ 17Human (Mammal) ~ 27Phosphorus (P) and Potassium (K) in shortest supply
Average 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 existed
Facts from R. Davies U. Penn.
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Leaving aside rare elements, all life hassimilar composition: (All % by number of atoms)
HCON Essential, most common P,S Also essential Ca Bones
Also Fe (Iron) HemoglobinMg (Magnesium) Chlorophyll
Human Beings61%26%10.5%2.4%0.13%0.23%0.13%
Bacteria63%29%6.4%1.4%0.12%
0.06%
ElementHydrogenOxygenCarbonNitrogenPhosphorusCalciumSulfur
SymbolHOCNPCaS
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Composition of the Earth:
Atmosphere
21%
78%
(0.011% Carbon)
Ocean
~ 33%
~67%
Crust
47%
28%
Element
Oxygen
Silicon
Nitrogen
Hydrogen
Question: Which is most similar to that of life?
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Composition of life more likeComposition of Sun (Universe)
% in Sun
93%
6.4%
0.06%
0.03%
0.011%
Element
Hydrogen
Helium
Oxygen
Carbon
Nitrogen
Symbol
H
He
O
C
N
Aside from He, HOCNWhere did these elements come from?
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The Drake Equation
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Drake 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 planets suitable for life on which life actually arisesfi = Fraction of life bearing planets where intelligence developsfc = Fraction of planets with intelligent life which develop a
technological phase during which there is a capacity for and interest in interstellar communication
L = Average of lifetime of communicable civilizationsr = Average distance to nearest civilization
*