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Unformatted text preview: dE r R START Asteroid Belt CHAPTER 4 THE CONDENSATION OF OUR SUN & THE ACCRETION OF THE PLANETS In the beginning, the Big Bang created the simplest of atomic nuclei, 1 H, 4 He, 2 H, 3 He, 3 H, 7 Be, 7 Li and 6 Li but nothing much else. All the more massive nuclei were created in the nuclear fires of stars. • Our planets are formed out of late materials = that have evolved through the growth/explosions of large stars (throughout the history of the universe) • Early Big Bang doesn’t create everything = only creates a few elements ( 3 He, 3 H, 7 Be, 7 Li) • Approximately 1 – 2 mil years after the Big Bang, large stars have formed (some are Super nova) = once at Super Nova, they produce the rest of chemistry From the dust of this nucleosynthetis, the elements of our Earth were formed and from these our Earth and Sun and planets condensed. • The rest of chemistry produced when a star is at Super Nova, gets scattered out into the dust clouds, H & He of the universe • Heavier elements get dispersed in and slowly get re-condensed into new sets of stars 4.1 THE CONDENSATION OF THE SOLAR SYSTEM About 5 × 10 9 years ago, when the universe was already, perhaps 8 × 10 9 years old, at some gravitational centre, material from the clouds of dust and gas left behind by supernoval explosions began to assemble the mass of our Solar System. • All elements known to exist in our Solar System, except for Promethium , 141-156 Pm, pre-existed in the condensing cloud. o Promethium = exists in the Solar system, but NOT on Earth (exists only in the Sun) Can be created synthetically through nuclear reactors, but doesn’t exist naturally on Earth. • Why no promethium on Earth? The longest-lived isotope of promethium, 145 Pm has a half-life, τ 1/2 of only 30 years and so all of this element would have been quickly lost to the cloud since no nucleosynthetic processes in the now cool cloud could produce it in replacement. • At the centre of this condensing cloud, a great mass of gas, largely hydrogen and helium began to form a proto-sun. • About the proto-sun, local centers of condensation formed orbits and concentrated the planets. o All stars have planetary like objects about them = we don’t know of any that don’t have a single planet around them • These proto-planets were brought into orbit because the condensing cloud possessed angular momentum and as the infalling material in the gravitational condensation approached the proto-sun, its angular momentum accelerated its rotation rate just as a figure skater accelerates her spin by pulling in her arms. • Angular momentum , usually designated, ⃗ L, is a conserved quantity 72 of physics. o Angular Momentum = quality of spin • Conserving angular momentum, the infalling dust and gas starts revolving ever faster....
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This note was uploaded on 01/09/2010 for the course EPSC 200 taught by Professor Jensen during the Winter '08 term at McGill.
- Winter '08