Terrestrial_Planets_-2_13Feb08

Terrestrial_Planets_-2_13Feb08 - Todays Presentation...

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1 Interiors of Terrestrial Planets Road Map: Planetary Densities Moments of Inertia Seismology Layered Structure of Planets Composition of Deep Earth Planetary Cores Planetary Mantles Planetary Crusts Planetary Differentiation Today’s Presentation 12 February 2007
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2 Internal Structure of a Terrestrial Planet In the previous discussion we talk about layered structure of the Earth – lithosphere and asthenosphere. The interior of the Earth has much more detailed structure than what we discussed before. The interior of the Earth is made 3 primary regions: A metallic core ( dominated by Fe, Ni and other elements) A silicate mantle ( largest zone by volme and made of silicates of Fe and Mg) Thin crust ( nerest to the surface ad made of Ca, Al, Na, K, Ti etc) The metallic composition of the Earth’s core was inferred long time ago from the composition of Fe meteorites. All terrestrial planets are inferred to have a sructuresimilar to that of the Earth – that means they have core, mantle and crust. Experimentally; How far can we reach using mines and Drill Holes ? Deepest Mines ~ 4 kms and Drill Hole ~ 6 km. This is a scratch on the surface of planet with a radius of ~6378 kms. So how do we find out about interior of Earth and other planets like it?
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4 Astronomical Measurements provide sizes and masses of planets. How we use Eq which periodicity of planetary rotation with time period. Densities of terrestrial planets differ from one another suggesting that they are not made of similar material but not same. The differences are partly due to pressure. How? There are two effects which one needs to consider: (i) Temperature (this expands the rocks) (ii) Pressure (this compresses the rocks) Because some planets are larger the rocks in the interior gets compressed. Therefore, rocks in the interior take up less space than otherwise if there were no pressure. In order to compare intrinsic density we need to correct for this pressure effect (which is not straight forward). The pressure profile in each planet is assessed, compression due to pressure is estimated, and expansion of rock in the absence of pressure is estimated. It is also necessary to take into account temperature. There are two ways of explaining the density difference: they contain different proportions of core, mantle and crust Since metallic core density > density of silicate mantle, different proportions of the two would produce planets of varying densities. Mantle and core have different composition in each planet and therefore densities of planets are Different.
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6 Note on Moment of Inertia-1: The moment of inertia, I of a body about a particular axis of rotation is a description of distribution of mass about this axis. I =
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This note was uploaded on 09/18/2010 for the course GLG 130 taught by Professor Srinivasan during the Spring '07 term at University of Toronto- Toronto.

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Terrestrial_Planets_-2_13Feb08 - Todays Presentation...

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