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Lecture 14

AS101 Lecture Notes - Lecture 14: Angular Momentum, Molecular Cloud, Space Debris


Department
Astronomy
Course Code
AS101
Professor
Patrick Mc Graw
Lecture
14

Page:
of 3
Astronomy Lecture 14
Scientific Method
- Science is a systematic way to investigate the physical world
Observations of the solar system
- Common plane, directions of revolution and rotation
- Two types of planets in the solar system
- Two types of space debris
- Radioactive dating
The Big Bang Theory
- 1. Making hydrogen and helium 15min
- 2. The universe to become transparent (400,000 years)
- 3. First stars form 4 mil years
- 4. 1st galaxy 1 bil years,
- 5. First and second generations of stars to enrich the universe with the other elements - 9 bil
years.
Star Formation
- Observation the visible surface of the sun and molecular clouds have the same composition
- Hypothesis the sun formed within a large, cool, rotating molecular cloud
- Temperature 10k, radius 4k to 40k AU
- If the gas in the cloud is compressed and become clumpy the force of gravity on other gas
particles increases more gas is attracted
- This core of gas continually grows hotter and denser until a star is born
The solar nebula theory
- Observation- the sun and all the contents of the solar system have a common age
- Solar system bodies share common rotations and revolution in the same plane
- Hypothesis 0 the planets formed in a rotating disk of gas and dust around a newly formed star.
How does a cloud make a disk?
- Gravity from the forming star pulls the particles inward
- The rotation of the particles increases as they fall inwards because of conservation of angular
momentum
- Angular momentum something is rotating and it is hard to stop it
- What happens when the masses moves toward the axis of rotation- it moves faster
- Particles above and below the star collide in the middle; this ends up making a flattened disk
- Reminds of a galaxy
- Prediction if all stars form like this, there should be disks ( and planets) around most other
stars
Different materials at different distances
- Observation two types of planets
- Higher densities closer to the Sun
- The solar nebula was mostly homogeneous but was warmer closer to the forming sun
- The gas must condense, or solidify
- Density increasing going closer to the forming sun
- Closer to the sun will have metals and metal oxides
Accretion just think snow
- Solid grains stick to each other and grow into larger particles
- Lots of planetesimals form, but larger objects grown faster
- Larger surface are for collisions
- Greater mass- stronger gravitational attraction
Terrestrial planet formation
- Formed via accretion over 30 mill years
- Differentiation- radioactive decay “melts” the planet
- Denser elements sink inward, less dense element float to form the crust
- Accretion of icy planetesimals
Jovian
- Ices are also present in the outer solar system
- Jovian planets can accrete more mass
- Since these plantetesimals are more massive they can use their larger force of gravitational
attraction to pull gas rapidly out of the nebula- hydrogen and helium interior/atmosphere
- Condensation- very first solidification of the gas to provide the seed.
Jovian Problem
- Observation most stars form in clusters
- Prediction disks may be evaporated by light from other stars before Jovian planets can grow
large enough
- Possible refinement if the disk is thick enough, jovian plaets could skip accretion, and grown
gravitationally
- If our disks become stable it starts to become clumps
Heavy bombardment
- sThe early solar system was filled with thousands of moon sized planetsimals and many smaller
objects.
- Off centre collisions probably caused:
- Venus’ retrograde rotation and Uranus’ tit/rotation
- Formed of earth’s moons
- A collision with a smaller object caused:
- The end of the Cretaceous period of the Earth 65 million years ago
Leftover construction material
- Observation = twp types of space debris
- Asteroids- remnants of rocky planetsimals that were disrupted by jupiters gravitational
influence
- Comets icry plantsimials that were either
- Scattered into outer solar system
-