AST101H5 Lecture Notes - Formation And Evolution Of The Solar System, Collision Theory, Tidal Force

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Published on 23 Nov 2011
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Astronomy Ch. 6 - Survey of our Solar System (Oct. 24)
Sun
- Sun is the heart of the solar system
- Sun’s radiation warms all the objects in the solar system
- Sun’s gravity holds the solar system together
- But, we will ignore the Sun (it is covered in AST201 as the nearest star) to focus on
everything else in the solar system
How large is the Solar System?
- Recall from Ch 1, “edge” of the solar system is about half way to the nearest star -
measured using parallax
- 100,000AU = 1.5 X 10^13 km
- “edge” varies because the Sun and the nearby stars move around
- This is far beyond Pluto or the new dwarf planets (“only” about 100 AU) or the comets
Major Planets
- Planets like Earth - “terrestrial” planets = Mercury, Venus, Earth and Mars
-close to the Sun warm
-small diameters small volumes
- small masses (Earth is most massive)
- large average densities = mass/volume 5 g/cm^3
-note: rock 3 g/cm^3 rock + metals
- few moons
- Planets like Jupiter - “jovian” planets = Jupiter, Saturn, Uranus and Neptune
-far from the Sun cold
-large diameters large volumes
- large masses: 14.5 to 318 X Earth’s mass
- small average densities 1 g/cm^3
- note: water 1 g/cm^3
- many moons
Dwarf Planets (New Class)
- Pluto (1930), Quaoar (2002), Sedna (2004), Orcus (2004), Eris (2005), Makemake
(2005) + ...
-beyond Neptune very cold
- tiny diameters (less than Earth’s Moon)
- tiny masses (less than Earth’s Moon)
- medium average densities 2 g/cm^3
"" contain a mixture of ice/rock
Other Members
- Small rocky objects
- Asteroids (minor planets)
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Nov. 18
Clues to the Formation
- We are trying to understand something that took place 4.5 billion years ago
- What clues can we see today that give us information about how the solar system
formed long ago?
- The general properties of the solar system, things that were caused by how the solar
system started
Systematic Properties of Orbits
- All large objects orbit counterclockwise when viewed from above Earth’s (and Sun’s)
north pole
- All large objects have nearly circular orbits - just slightly elliptical
- Most larger objects spin in their orbit direction = counterclockwise
- Most orbits are nearly align with the Sun’s equator = a solar system’s plane
- Most of the larger moons share these traits:
-counterclockwise orbits
-counterclockwise spin
-aligned above their planet’s equator
Systematic Physical Trends
-Rocky terrestrial planets are all close to the Sun
-Gas jovian planets are all far from the Sun
-Icy dwarf planets are all very far from the Sun
-Properties of the asteroids and comets
Deviations from the Trends
-Most planets spin counterclockwise, same as their orbit direction, but not Venus and
Uranus
-Comets have very elliptical orbits
-Most moons are much smaller than their planet, but Earth’s Moon is similar in size
Theories of the Solar System must be flexible enough to handle these deviations
Theories of Formation
Nebular Theory
- Kant 1755, Laplace 1800
- Nebula (cloud in Latin) of gas (H, He, ...) with a small amount of dust
- Nebula’s diameter 200,000 AU
- Pulled together by its own gravity to form the Sun - planets, asteroids and comets form
around it in a flattened disk
Collision Theory
- 1900
- Our sun formed without planets
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Document Summary

6 - survey of our solar system (oct. 24) Sun is the heart of the solar system. Sun"s radiation warms all the objects in the solar system. Sun"s gravity holds the solar system together. But, we will ignore the sun (it is covered in ast201 as the nearest star) to focus on everything else in the solar system. Recall from ch 1, edge of the solar system is about half way to the nearest star - measured using parallax. Edge varies because the sun and the nearby stars move around. This is far beyond pluto or the new dwarf planets ( only about 100 au) or the comets. Planets like earth - terrestrial planets = mercury, venus, earth and mars. Planets like jupiter - jovian planets = jupiter, saturn, uranus and neptune. Large average densities = mass/volume 5 g/cm^3. Note: rock 3 g/cm^3 rock + metals. Large masses: 14. 5 to 318 x earth"s mass.

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