AST 248 Lecture Notes - Lecture 22: Gravitational Lens, Tropopause, Sagittarius Window Eclipsing Extrasolar Planet Search
1 Aug 2016
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Sun has sufficient main sequence lifetime for life to develop and evolve. Earth has the right dista(cid:374)(cid:272)e fro(cid:373) the u(cid:374), i. e. , is i(cid:374) (cid:862)ha(cid:271)ita(cid:271)le zo(cid:374)e(cid:863). Li(cid:373)its deter(cid:373)i(cid:374)ed (cid:271)y runaway greenhouse and refrigerator effects. The size of earth large enough formed with significant but not too large atmosphere. Varying luminosity of sun compensated by greenhouse effect. Has large (cid:373)oo(cid:374) that produ(cid:272)es sig(cid:374)ifi(cid:272)a(cid:374)t tides a(cid:374)d sta(cid:271)ilized earth"s spi(cid:374) a(cid:454)is. Jupiter and other giant planets removed asteroids and comets from earth-crossing trajectories, reduced cometary impact rate during last few billion years. But jupiter also prevented a planet from forming, resulting in asteroids. Solar composition has c/o < 1 (0. 55), so free oxygen is available. Existence of plate tectonics also contributes to climate stability, being an important part of the. Plate tectonics are possible for earth-sized planets containing water. This is (cid:272)aused (cid:271)(cid:455) i(cid:374)(cid:272)reasi(cid:374)g a(cid:373)ou(cid:374)t of he ash i(cid:374) u(cid:374)"s (cid:272)ore whi(cid:272)h redu(cid:272)es abundance of h fuel.
