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Lecture 18

ASTA01H3 Lecture Notes - Lecture 18: Silicon Dioxide, Terrestrial Planet, Outer Core


Department
Astronomy
Course Code
ASTA01H3
Professor
Kristen Menou
Lecture
18

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Chapter 13: Comparative Planetology of the Terrestrial
Planets
Lecture 18
-the comparison of one planet with another is called comparative planetology
-it is one of the best ways to analyze the worlds in our solar system
Five Worlds
-the first feature to notice is diameter
-the Moon is small
-Mercury is not much bigger
-Earth and Venus are large and similar in size to each other
-Mars is medium-sized
-size is a critical factor in determining a worlds “personality”
-small words tend to be internally cold and geologically dead
-larger worlds can be geologically active
Core, Mantle and Crust
-the terrestrial worlds are made up of rock and metal
-they are all differentiated:
-rocky, low density crusts
-high-density metal cores
-mantles composed of dense rock between the cores and crusts
-cratered surfaces are old
-one important way you can study a planet is by following the energy
-the heat in the interior of a planet may be left over from the formation of the planet
-it may also be heat generated by radioactive decay
-in any case, it must flow outward toward the cooler surface where it is radiated into
space
-in flowing outward, the heat can cause phenomena such as:
-convective motions in the mantle
!1
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-magnetic fields
-plate motions
-quakes
-faults
-volcanism
-mountain building
-heat flowing upward through the cooler crust makes a larger world like Earth
geologically active
Atmospheres
-when you look at Mercury and the Moon, you can see their craters, plains and
mountains
-the surface of Venus is completely hidden by a cloudy atmosphere even thicker than
Earth’s
-Mars, the medium-sized terrestrial planet has a relatively thin atmosphere
Earth: Planet of Extremes
-Earth is an active planet
-it has a molten interior and heat flowing outward to power volcanism, earthquakes,
and an active crust
-almost 75% of its surface is covered by liquid water
-the atmosphere is N2 dominated (70% by mass)
-it contains a significant amount of molecular oxygen (almost 21% O2)
Earth’s Interior
-Earth’s mass divided by its volume gives its average density — 5.52 g/cm^3
-however, the density of Earth’s rocky crust is only about half that
-clearly, a large part of Earth’s interior must be made of material denser than rock
-each time an earthquake occurs, siesmic waves travel through the interior and
register on seismographs all over the world
-analysis of these waves shows that Earth’s interior is divided into:
-a metallic core
-a dense rock mantle
-a thin, low-density crust
!2
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