Astronomy 1021 Chapter Notes - Chapter 6: Interstellar Cloud, Kelvin, Oort Cloud

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16 Aug 2016
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Chapter 6: Formation of the Solar System
Solar System and Telescopes
All 3 techniques used in study of solar system
oImaging
oSpectroscopy
oTiming
Measuring sizes
With the aid of telescopes, we can measure the angular diameter of planets
Since we also know the distance, we can calculate the diameter in kilometers
Measuring masses
Observe moons going around planet > measure angular distances & orbits and periods > tells
you mass of planet
From mass & size: we get density, tells us material and distribution
Rotation
Infer rotation by watching planet's appearance change over time
Telescopes and spacecraft
Pros and cons
Solar System
8 planets
170+ known moons
5+ dwarf planets
Billions of smaller bodies
Sun
Mostly hydrogen and helium
Contain 99.9% of solar system's mass
Mercury
Metal and rock
Large iron core
Bit bigger than moon
Desolate, cratered; long tall steep cliffs
425C (day), -170C (night)
Venus
Nearly identical in size to Earth but has surface hidden clouds
Rotates clockwise very slowly, one venus day = 243 Earth days
Hellish conditions deu to extreme greenhouse effect
470C day and night
Earth
Only surface liquid water in solar system
Surprising large moon
Only known place with life
Most known extrasolar planets are more massive than earth
Mars
Cold desert
Giant volcanoes, huge canyon, polar caps, etc
Water flowed in distant past
Number of active Mars missions
Jupiter
More massive than all other planets combined, 300x earth's mass
Mostly hydrogen and helium, no solid surface
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Many moons, rings
Moons
oIo: most volcanically active body
oEuropa: possible subsurface ocean
oGanymede: largest moon in solar system
oCallisto: large cratered "ice ball"
Saturn
Giant and gaseous like Jupiter
Spectacular rings and many moons
Rings are made of many small chunks of ice and rock
Uranus
Ice giant
Smaller than jupiter and saturn but larger than earth
Made of hydrogen/helium gas and hydrogen compounds
Extreme axis tilt, 90 degrees
Moons and rings
Neptune
Colder and less axis tilt compared to Uranus
Many moons
Moon Triton:
oBigger than pluto
oOrbits backwards
Pluto (other dwarf planets)
Icy and much smaller than major planets
Pluto's main moon (Charon) is almost as big as Pluto
Planet Densities
Study Table 7.1
Know the meaning of properties
Which planets have extreme properties
Know the compositions of planets
Know moons of terrestrial planets
oWhich planet has the most moons
oSpecial moon names
oEtc
Dwarf Planets
Currently 5
oCeres
oPluto
oHaumea
oMakemake
oEris
Objects are massive enough to be rounded by their own gravity
We only know Ceres and Pluto are round
The Nebular Theory of Solar System Formation
1. Patterns of Motion Among Large Bodies
oAll planetary orbits are nearly circular and lie nearly in the same plane
oAll planets orbit the sun counter clockwise
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oMost planets rotate in the same direction in which they orbit, with fairly small axis
tilts. The sun also rotates in this direction
oMost of the solar system's large moons exhibit similar properties in their orbits
around their planets, such as orbiting in their planet's equatorial plane in the same
direction that the planet rotates
2. Two Major Types of Planets
oTerrestrial planets
Mercury, Venus, Earth and Mars
Relatively small and dense, rocky surfaces and an abundance of metals in
their cores
Few moons, if any
Our moon has been shaped by the same processes that shapes terrestrial
planets
oJovian planets
Jupiter, Saturn, Uranus, Neptune
Much larger in size, lower in average density
Have rings and many moons
Lack solid surfaces: made mostly of hydrogen, helium and hydrogen
compounds (compounds containing hydrogen such as water, ammonia,
methane)
Terrestrial planets Jovian planets
Smaller size and mass Larger size and mass
Higher density Lower density
Made mostly of rock and metal Made mostly of hydrogen, helium and
hydrogen compounds
Solid surface No solid surface (“gas giants”)
Few (if any) moons and no rings Rings and many moons
Closer to the Sun and closer
together, with warmer surfaces
Farther from the Sun (and farther apart)
with cool temperatures at cloud tops
1. Asteroids and Comets
oAsteriods
Rocky irregularly shaped bodies that orbit the sun like planets, but are
much smaller
Largest asteroids are smaller than our moon
Most known asteroids are within asteroid belt between orbit of Mars and
Jupiter
Duck specks to dwarf planet sizes (950km diameter)
oComets
Small objects that orbit the sun
Made largely of ices (water ice, ammonia ice, methane ice) mixed with rock
May be visible to naked eye, but vast majority never visit inner solar
system
Orbit the sun in one of two distinct regions
Kuiper belt
Donut-shaped region behind orbit of neptune
Orbit in same direction and plane as planets
Pluto and Eris are largest known
Oort cloud
Much farther from the sun
May contain a trillion comets
Comets have random orbits, giving cloud a roughly
spherical shape
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