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Lecture

7.2 Patterns in the Solar System


Department
Astronomy & Astrophysics
Course Code
AST101H1
Professor
C.B.Netterfield

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7.2 Patterns in the Solar System
-Features that provide clues to how our solar system provide clues to how it formed?
Æ Feature 1: Patterns of motion among large bodies
-the theory of solar system formation explains all these patterns as consequences of processes that
occurred during the very first stages of the birth of our solar system
-all planetary orbits are nearly circular and lie nearly in the same plane
-all planets orbit the Sun in the same direction: counterclockwise as viewed from high above
(DUWK·V1RUWK3ROH
-most planets rotate in the same direction in which they orbit, with fairly small axis tilts
-PRVWRIWKHVRODUV\VWHP·VODUJHPRRQVH[KLELWVLPLODUSURSerties in their orbits around their
planets
Æ Feature 2: The existence of two types of planets
-Terrestial planets (Earth-like)
-four planets of the inner solar system (Mercury, Venus, Earth and Mars)
-relatively small and dense, rocky surfaces and an abundance of metals deep in their
interiors
-few moons, no rings
-Jovian planets (Jupiter-like)
-four planets of the outer solar system (Jupiter, Saturn, Uranus and Neptune)
-much larger in size and lower in average density
-numerous moons and rings
-mostly made of hydrogen, helium and hydrogen compounds
-sometimes referred to as gas giants
-do not have solid surfaces and look like balls of gas from the outside
Æ Feature 3: Asteroids and Comets
-Asteroids
-small, rocky bodies that orbit the Sun much lie planets but are much smaller than planets
-most found within the asteroid belt between the orbits of Mars and Jupiter
-Comets
-small objects tat orbit the sun, but are made largely of ices (water ice, ammonia ice, and
methane ice) mixed with rock
-the vast majority of comets never visit the inner solar system, instead orbiting the Sun in
the extreme outer reaches of the solar system where they remain frozen and lack tails
-two groups of comets:
-one group orbits the Sun in the same direction and nearly the same plane as the
planets (occupies a broad region beyond the Kuiper Belt
-the other group does not show any simple pattern to its orbits and resides much
further from the Sun in a region called Oort cloud
Æ Feature 4: Exceptions to the rules
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-Venus rotating backward
-many small moons have much more unusual orbits
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