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36-DrakeEqnDebate - Is Extraterrestrial Intelligence Common...

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Is Extraterrestrial I t lli C ? Intelligence Common? Bi l 190A Biology 190A Lecture 40 ‐‐‐ Prof. Steve Schneider Dept. of Astronomy
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The Copernican Principle vs. The Rare Earth Hypothesis Much of the progress of scientific thinking since the 1500s has been made as a result of recognizing that our place in the Universe is like almost any other. But is the Earth really a very average place or is it extraordinarily unique?
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Essential or Incidental? – 1 • The Sun is a particular type of star that is more luminous and more massive than about 99% of all stars but still lasts long enough for life to form. – The great majority of stars live longer, but have such low luminosities that a planet would have to lie very close to them for liquid water to be present. – At such small distances, the planet would become “tidally locked” with one face always toward the star. However, with a thick atmosphere (as on Venus), the temperature evens out over the planet even if it rotates l l very slowly .
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Essential or Incidental? – 2 • The amount of heavy elements in the Solar System is critical to the formation of earthlike planets. – With much less, no planets form, and most stars formed earlier than the Sun with less heavy elements. However, heavy element amount rose quickly. – With much more, so many giant planets form that they are likely to swallow or knock out smaller planets. However, reasonable sized planets may end up as satellites of the giant planets, and besides, this is only true of recently formed stars, which haven’t been d l h f i ili i f around long enough for civilizations to form.
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Essential or Incidental? – 3
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