02_OriginSolarSys - GEL36 SOLAR SYSTEM Lecture 2: Origin of...

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1 GEL36 SOLAR SYSTEM Lecture 2: “Origin of the Solar System” (Ch. 19, p. 396-400, p. 407-423) Goal of the Lecture: To use the fundamental characteristics of the solar system as support for the solar nebula hypothesis for the origin of the solar system. Second goal is to discuss planetary evolution within the context of condensation from the solar nebula. I: Origin of the Solar System Solar Nebula Hypothesis Nebula are clouds of gas and dust in space that mark the birthplace of stars ("star nurseries"). - the dust is composed of small amounts of various ices, oxides, carbon and some heavier elements such as iron. (size of the dust is about the size of smoke particles, just a few atoms big) - the gas is almost entirely hydrogen (which you know as the simplest element, consisting of one proton and one electron). - hydrogen makes up about 75% of all the mass in the universe. Elemental abundance in cosmos (Fig. P-14 in textbook, 7 th ed., figure P-11 in 6 th ed.) shows the dominance of hydrogen and helium on both the log plot and linear plot. H and He dominate the sun and the Jovian planets. Note the common occurrence of C, N, O (the stuff of life) and the relative abundance of Si, Al, Mg, Ca, Fe, S, Na, K that form rocky planets and moons. - “the atoms of which we are made are just a tiny impurity in the cosmos” - the elements we’ll talk about most in this class are the common ones that comprise a large part of the solar system: H, He, O, Si, Fe, C, N (if you don’t recognize the element symbol, look them up in the index at the back of the book) Nebula are “star factories” and the solar nebula from which our solar system formed was a fragment of a larger interstellar gas cloud. * The solar nebula hypothesis "proposes that the planets were formed from the disk of gas and dust that surrounded the sun as it formed." (i.e., planets form as a byproduct of star formation from nebula.)
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2 Stages in the formation of the solar system . . . (this model applies to all stars) (You just need to understand the major concepts behind this model. Don’t sweat the details or the exact sequence of events.) - this process occurs over millions of years . . . . 1) Begin with a slowly spinning cloud of gas and dust ( solar nebula ) within the Milky Way galaxy. 2) The spinning nebular cloud begins to collapse toward its rotating center under the influence of gravity, forming a dust disk (aka gas disk) . ( Gravity is the dominant force in the universe.) 3) As the cloud collapses, gravity supplies the energy to heat up and compress the center. The nebular cloud heats up because the velocity of the atoms falling inward is so great . (Temperature is proportional to velocity of atoms in a material – the faster the vibration of an atom, the higher its temperature.) - most of the nebular gas and dust fall inward toward the central concentration, which eventually becomes the “protosun”. Protosun still surrounded by a tenuous cocoon of gas and dust at this stage, but with a greater concentration along the rotating central plane. 4) Inward motion of gas and dust causes an increase in the speed of rotation of the
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This note was uploaded on 05/31/2011 for the course GEL 36 taught by Professor Osleger,d during the Spring '08 term at UC Davis.

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02_OriginSolarSys - GEL36 SOLAR SYSTEM Lecture 2: Origin of...

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