Astronomy 1021 Chapter Notes - Chapter 19: Kic 8462852, Dyson Sphere, Volcanism
28 May 2018
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Astronomy 1021
Chapter 19: Life in the Universe
Life Around Other Stars
Requirements for Surface habitability
•The habitable zone- the range of distances from the Sun at which a planet like Earth could have oceans and
surface life
•Volcanism and Plate Tectonics- a planet in the habitable zone must also be large enough to have substantial
plate tectonics and volcanism
•Global Magnetic Field- planet needs to be able to maintain this; thus it needs enough internal heat to
maintain core convections and fast enough rotation to twist and distort the convection pattern
Life Outside Solar System?
•Tabby’s Star: named after astronomer Tabetha S. Boyajian; KIC 8462852, “where the flux” star
oWhy is Tabby’s star so strange?
•Possible explanations- debris after planetary collision; swarm of comets; dyson sphere- sun produces a lot
of energy but only a small portion gets absorbed by the earth; so idea is that we should build a structure
around the Earth (sphere) that intercepts more energy than Earth can
•Search for Extraterrestrial Intelligence (SETI)- tries to find origins of weird signal of Tabby; tries to look
for alien life outside the Earth; tries to find other civilization
•Drake Equation- Frank Drake in 1961; N, the number of civilizations capable of interstellar communication
in our Galaxy; useful for not solving, but for contemplating; N = "R"∗ fp np fl fi fc L
oMakes us think about what factors we need to find life
oN= number of civilizations capable of interstellar communication in our galaxy
oR= average rate of star formation in Milky Way (1-3 stars/year); fp= fraction of stars that have
planets; np= average number of planets per star that can potentially support life; fl= fraction of
planets that develop life
oFi= fraction of planets bearing life on which civilized life has developed; fc= fraction of
civilizations that have developed communications; L= time over which such civilizations release
detectable signals
•Fl= if Fl is 1, then can develop life easily, if number is 0, it is hard to develop life (we just got lucky on
Earth); we only have one example so cannot extrapolate
•Fi; i stands for intelligent conversation; fi= 0 means unlikely to find civilized life; if number is 1 it is
inevitable
•Fc= we are not actively communicating, only passively; only detectable within one light-year away
•L= can we avoid self-destruction? Is there some point where we, as a civilization, can become immortal?
•The Numbers: estimates for N range from Earth being the only example in the universe, to 10s of millions
oWhy can’t we explore the stars? Where are the aliens?
•Slow spacecraft speeds
Document Summary
Fi= fraction of planets bearing life on which civilized life has developed; fc= fraction of civilizations that have developed communications; l= time over which such civilizations release detectable signals. Fl= if fl is 1, then can develop life easily, if number is 0, it is hard to develop life (we just got lucky on. Earth); we only have one example so cannot extrapolate. Fi; i stands for intelligent conversation; fi= 0 means unlikely to find civilized life; if number is 1 it is inevitable. Fc= we are not actively communicating, only passively; only detectable within one light-year away.
