Chapter 6 Our Solar System and Its Origin How was the Solar System Formed? A viable theory for the formation of the solar system must be based on physical principles (conservation of energy, momentum, the law of gravity, the law of motions, etc.), able to explain all (at least most) the observable facts with reasonable accuracy, and able to explain other planetary systems. How do we go about finding the answers? Observe: looking for clues Guess: come up with some explanations Test it: see if our guess explains everything (or most of it) Try again: if it doesn’t quite work, go back to step 2.

What does the solar system look like from far away? NASA Figure Sun, a star, at the center… Inner Planets (Mercury, Venus, Earth, Mars) ~ 1 AU They are all rocky planets… Asteroid Belt, ~ 3 AU Outer Planets (Jupiter, Saturn, Neptune, Uranus), ~ 5-40 AU They are all gaseous planets.. Pluto: odd ball planet, more like a comet… Keiper Belt ~ 30 to 50 AU Oort Cloud ~ 50,000 AU Where comets come from… Cool link about solar system: http://liftoff.msfc.nasa.gov/academy/space/solarsystem/solarsystemjava.html

Clues - The Orbits of the Planets All the planets orbit the Sun in the same direction The rotation axes of most of the planets and the Sun are roughly aligned with the rotation axes of their orbits. Orientation of Venus, Uranus, and Pluto’s spin axes are not similar to that of the Sun and other planets. Why do they spin in roughly the same orientation? Why are they different?

Summary - What do the inner planets look like? They are all… rocky and small! No or few moons No rings

Summary - The Jovian Planets They are all… gaseous and BIG! Rings Many moons

Common Characteristics and Exceptions of the Solar System We need to be able to explain all these!

The Nebular Theory* of Solar System Formation Interstellar Cloud (Nebula) *It is also called the ‘Protoplanet Theory’. Protoplanetary Disk Protosun Gravitational Collapse Metal, Rocks Condensation (gas to solid) Sun Gases, Ice Heating  Fusion Terrestrial Planets Accretion Nebular Capture Jovian Planets Asteroids Leftover Materials Comets Leftover Materials

It starts from a Nebula… Nebula- large cloud of gas and dust Mostly Hydrogen and Helium P.O.C- (light years in length) Horsehead Nebula (Infrared Image)

Why are they there in the first place? Carina Nebula Lagoon Nebula

https://www.youtube.com/watch?v=Uhy1fucSRQI

Supernovas or Novas Supernova- an explosion from the result of the death of a star Provides material (elements) for nebulae The Helix Nebula (Recognize it?) Infrared Light Crab Nebula- a supernova remnant (Visible light)

1. Gravitational Collapse Thought to be started by a Supernova OR thought to be started by overdensity Starts very slowly at first, but as it collapses the rotation begins to move faster…

Conservation of Angular Momentum Spinning speed increases as you move mass towards the middle https://www.youtube.com/watch?v=tFLOsRSuW0E

Collapse Continued As collapse furthers, speed increases and kinetic energy increases Faster particles start ‘dominating’ the direction of the spin, force others to go in their direction Remember this video https://www.youtube.com/watch?v=MTY1Kje0yLg (2:50)

http://www.nowykurier.com/toys/gravity/gravity.html

Why all planets revolve,rotate in the same direction This explains… Why all planets revolve,rotate in the same direction

2. Protosun (Part B in pic) Eventually, the collapse causes a huge increase in heat and pressure Fusion begins, and a sun formed in the middle of the cloud

3. Protoplanetary Disk The rest of the cloud that didn’t form the sun Why is it all on the same plane? (Part B&C)

Same reasons as the physics of this…

Or this…

Why all the planets exist on the same plane This explains... Why all the planets exist on the same plane

4. and 5. Condensation/Accretion Condensation: Gas turning into liquid or solid particles due to cooling Accretion: Process in which liquid/solid particles ‘stick together’ and form larger pieces Planetesimals: Small, planet-like bodies formed from accretion

The Nebular Theory* of Solar System Formation Interstellar Cloud (Nebula) *It is also called the ‘Protoplanet Theory’. Protoplanetary Disk Protosun Gravitational Collapse Metal, Rocks Condensation (gas to solid) Sun Gases, Ice Heating  Fusion Terrestrial Planets Accretion Nebular Capture Jovian Planets Asteroids Leftover Materials Comets Leftover Materials

Gravitational Collapse A Pictorial History Gravitational Collapse Interplanetary Cloud Condensation Accretion Nebular Capture

Asteroid Belt Asteroid Belt: Leftover material within the frost line that did not accrete into a planet Frost line: Area within which heavy metals can condense into liquid/solids (3.5 AU) Inside frost line = metallic elements Outside frost line = hydrogen compounds, helium, hydrogen

Why no accretion? https://www.youtube.com/watch?v=-BMoD7k7q4o

Jovian Planet Formation: Step by Step Accretion- Just like terrestrial planets, only this material is composed of hydrogen compounds (Water, Methane) Planetesimals are much LARGER than terrestrial planetesimals. Why? (Think composition)

3. Nebular Capture 3. Nebular capture- Gases being ‘captured’ by Jovian planets’ gravitational pull Nebular capture happens after accretion

Nebular capture More mass = more gravity Planets have enough mass to attract hydrogen and helium gas Remember- 71% Hydrogren

In conclusion… Accretion of icy compounds Planetesimals became massive enough to attract hydrogen and helium Planetesimals attracted TONS of the two gases through nebular capture Jovian Planets formed

Terrestrial Planets? Did not attract Hydrogen and Helium because their mass was much too low to attract Hydrogen and Helium (Two lightest elements) So they do not have a large gaseous area of these two gases Explains size difference

Kuiper Belt

Kuiper Belt Similar to asteroid belt… “Dirty snowball-” an asteroid with icy compounds on it Leftover material that did not accrete into a jovian planet https://www.youtube.com/watch?v=XjW6k--6Oi0

In summary… https://www.youtube.com/watch?v=efbdqPRVX9c