Formation of the Solar System

Which one is bigger

• solar system

• Galaxy

Galaxy

Solar system

Refers to system surrounding the sun, different from galaxy

Galaxy

Collection of many different suns and stars (billions of solar systems)

Scale of solar system

Hard to get a good pic of solar system because the scale is huge

• planets are tiny compared to the distances between them

• Can’t show both accurate sizes of planets AND accurate distances, can only show one or the other

Watch the YouTube video

Yessir

Watch “To Scale: The Solar System”

Yippee

Properties of our solar system

1. The sun, planets, and large moons orbit and rotate in an organized wat

2. Two types of planets (terrestrial and Jovian)

3. Asteroids and comets

Sun, planets, and large moons orbit

Orbits are nearly circular and lie in the same plane

Terrestrial planets

• Small, rocky, and close to the sun

• Smaller size and mass

• Higher density

• Made mostly of rock and metal

• Solid surface

• Few (if any) moons and rings

• Closer to sun (and closer together), with warmer surfaces

• ex. Earth

Jovian planets

• Large, gas rich, and far from the sun

• Larger size and mass

• Lower density

• Made mostly of hydrogen, helium, and hydrogen compounds

• No solid surface

• Rings and many moons

• Farther from the sun (and farther apart), with cool temperatures at cloud tops

What are rings made of

A bunch of rocks from moons that didn’t form

Watch the Saturn video

Wowowow

Which planets in our solar system are Jovian

Jupiter, Uranus, Saturn, Neptune

Asteroids and comets

• Rocky asteroids

• Icy asteroids

• Far outnumber the planets and their moons

Rocky asteroids

Between mars and Jupiter

Icy asteroids

In vicinity of Neptune and beyond

Summary of properties

1. Large bodies have orderly motions

2. Two types of planets

   1. Small, rocky terrestrial planets

   2. Large, hydrogen-rich Jovian planets

3. Swarm of asteroids and comets exist in certain regions

Nebula

Cloud of gas in space

• hydrogen and helium most abundant gas in universe

Interstellar

In between stars

Nebular theory

The solar system formed from giant cloud of interstellar gas

• gas has mass, anything that has mass has gravity (an attractive force)

• If you have a cloud of gas with enough mass, the force of gravity will try to collect it to make it smaller

What happens when gravity causes the gas to shrink

The cloud will begin to spin faster and faster

• because of conservation of angular momentum (radius decreases)

• Cloud heats up because of conservation of energy

• Collapses into a disk

What happens when the gas mass collapses into a disk

Disk rotated in the same direction as the nebula, but faster

• then planets formed from the material in the disk

• Planets inherited their motion from the disk, so they rotate in the same direction

• This explains why large bodies have orderly motions!

Orderly motions in solar system

• sun formed in center of nebula

• Planets formed in the disk

• Explains the following

  • All planets lie in one plane (in the disk)

  • All planets orbit in one direction (the spin direction of the disk)

  • Sun rotates in same direction

  • Planets tend to rotate in this same direction

  • Most moons orbit in this direction

  • Most orbits are nearly circular (Collisions in the disk)

Planetesimals

Tiny solid particles stick to form this

• start in random directions, and eventually gravity makes them stick together into a ball

explain relationship between planetesimals and planets

gravity draws planetesimals together to form planets

What are planets formed from

From solid chunks

What kind of solid materials exist in the protoplanetary disk? How much material is available to form planets?

Depends on the temperature

Solar nebula (and most things in the universe) made of:

• hydrogen and helium gas (98%)

• Hydrogen compounds, like NH3 and CH4 (1.4%)

• Rock and metals (.6%)

Condensation

The formation of solid or liquid particles from a cloud of gas

When do hydrogen and helium condense

Never condense in nebulae

When do hydrogen compounds condense

Condense at low temps

When do rock and metal condense

Higher temperatures

If you move further away from the sun in the early solar system, how would you expect temperature to change

It decreases (gets colder) with distance from the center

Frost line/snow line

• in a young solar system, temp changes with distance

  • Close to the star, it is too warm for ices to survive

  • Farther out, ices can form and remain solid

• The transition is called this

What materials can condense (form solids) INSIDE the frost line

Rocks, metals [hydrogen compounds stay gaseous]

What does the amount of solid material available to form planets depend on

The temp of the disk

What materials can condense (form solids) INSIDE the frost line

Hydrogen compounds, rocks, metals

Why does the frost line matter

the frost line affects what kinds of materials are available to build planets

Inside frost line

Mostly rock and metal

Outside frost line

Rock, metal, AND ice (easier to build planets)

Where do you expect to find more solids of any kind from which to build planets

Beyond (outside) the frost line

What happened to the planets formed beyond the frost line

Grew much bigger because they had more solid material to build from

Terrestrial planets formation

Dust —> pebbles —> rocks —> boulders —> planetesimals —> create a massive icy rocky core with more gravity (which can hold more gas), making a terrestrial planet

Jovian planets formation

Icy dust —> icy pebbles —> icy rocks —> icy boulders —> icy planetesimals → icy/rocky core —> capture gas —> Jovian planet

Key difference between icy/rocky cores and terrestrial planets

icy/rocky cores have much more mass than terrestrial planets. More mass means more gravity. Icy/rocky cores are able to capture lots of gas

more mass means…

more gravity, and all that gravity means it was easy to capture lots of gas (H and He)

how did moons of jovian planets form

miniature disks formed inside disks, those became moons

modern picture of planet formation

planets form in disks of gas and dust around young stars

• temp affects what materials are available

• but disks change over time

• material moves around

• planets can migrate

some planets probably did not form where we see them today

where did comets and asteroids come from

they are leftover planetesimals, the solar wind blew away leftover gases

solar wind

outflowing matter from the sun

why are asteroids rocky

because they formed inside frostline

why are comets icy

because they formed outside frostline

read 14.3 (solar nebula, but also all of it), but also 7.1-7.2

yessir