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Are We Alone.ppt - Are We Alone? Lecture 5D 6/26/19 Recap...

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Are We Alone?Lecture 5D6/26/19
Recap of 6/26What were conditions like in the earlyuniverse?What is the history of the universeaccording to the Big Bang Theory?Is there any evidence for the Big Bang?How does inflation explain the BigBang?
Are We Alone?Our learning goals:What qualities on another world doscientists believe are necessary forlife?Does primitive life exist elsewhere?How do scientists detect planets?Are Earth like planets rare orcommon?
EARLY Believers of E.T.Metrodorus of Chios, a Greek philosopher (4thcentury B.C.E) - “To consider the Earth as the onlypopulated world in infinite space is as absurd as toassert that in an entire field of millet, only one grainwill grow.”Epicurus, (300 B.C.E) - “There are infinite worldsboth like and unlike this world of ours...We mustbelieve that in all worlds there are living creaturesand planets and other things we see in this world.”Italian Giordano Bruno, (1600s)- “There arecountless suns and countless earths all rotating abouttheir suns in exactly the same way as the sevenplanets of our system...The countless worlds in theUniverse are no worse and no less inhabited than ourEarth”.
What qualities on a world doscientists believe are necessaryfor life to exist there?
Habitable PlanetsDefinition:Ahabitableworld contains thebasic necessities for life as we knowit, including liquid water.It doesnotnecessarily have life.
Constraints on star systems:1)Old enough to allow time for evolution(rules out high-mass stars - 1%)2)Need to have stable orbits (mightruleout binary/multiple star systems -50%)3)Size ofhabitable zone”: region inwhich a planet of theright sizecouldhave liquid water on its surface.Even so… billions of stars in the Milky Way seemat least to offer the possibility of habitable worlds.
The more massive the star,the larger the habitable zone— higher probability of aplanet in this zone.
Qualities Necessary for Lifeto Exist:Earth is an unusually suitable planet forcomplex life vs. extrasolar planets, why?(ref. chapter 8 of your online textbook)Hot Jupiters
Hot Jupiters
Qualities Necessary for Lifeto Exist:Earth is an unusually suitable planet forcomplex life vs. extrasolar planets, why?

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Planet, Extraterrestrial life, Extrasolar planet

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