Origin of the Solar System

Astronomy 311Professor Lee

CarknerLecture 8

Quiz 1 Monday Covers lectures 1-8 and associated readings About half multiple choice (~20 questions), half

short answer/problems (~4 questions) Study:

Notes Can you write a paragraph explaining each major concept?

Exercises Can you solve all the exercises with no resources?

Readings Can you do all the homework with no book and Quizdom

questions with no notes?

Bring pencil and calculator! No sharing!

The Solar System

Questions When did it form? Why does it have structure?

Structure of the Solar System

The solar system has three distinct regions

Mercury, Venus, Earth, Mars, Asteroids Made of metal and rock

Outer region Jupiter, Saturn, Uranus, Neptune and Moons Made of ice and gas

Kuiper Belt and Oort Cloud Made of ice

Where Did the Solar System Come From?

We can’t look back in time to see how the Sun and planets formed, but we can look at young stars that are forming today

Star Formation

Due to an external stimulus (e.g., supernova shockwave, stellar wind)

Gravity causes the core to contract to a star

Conservation of angular momentum makes the clump spin faster Rapid rotation causes the outer layers to form a disk

Circumstellar Disks

Disks are fairly cool and can be detected with infrared and millimeter telescopes

Disks are common around young stars

From Disks to Planets

Where does the disk go? Formed into planets

Disks you can see, planets you can’t

How Do Planets Form?

There are 4 stages to planet formation grains stick together to form

planetesimals gas and leftover planetesimals are

cleared from solar system

What Was the Solar Nebula Made of?

Solar Nebula --

From studying meteorites and star forming regions we hope to discover what the solar nebula was made of

Two basic components Gas -- Dust -- made of rock (silicates), metal (iron) and

ices (water, methane, ammonia, carbon dioxide)

Solar System Dust Grain

Accretion of Grains

Grains get larger by sticking together and settle to the center of the disk

Eventually the grains form into larger bodies (a few km in size) called planetesimals At the end of this stage the solar system is populated by a few

thousand planetesimals, such a system is invisible to telescopes

Accretion in a Protoplanetary Disk

Star

Disk

High Density LowDensity

Larger Grainsmove to center

Temperature and the Solar Nebula

Two basic types of dust in solar nebula: Volatiles -- Refractory Material --

Temperatures were higher in the inner solar system and lower in the outer solar system

Inner solar system -- rocky planetesimals Outer solar system -- icy planetesimals

Regions of Formation Temperature

Rocky Icy

Gas

Planetesimals to Planets

Due to gravity and intersecting orbits the planetesimals collide with each other

Planet formation happens differently in inner and outer solar system

Formation of Gas Giants In the outer solar system you have more

material (both volatiles and refractory material), so planets are larger

No more hydrogen gas after a few million years Thus, in the outer system where the

temperatures are lower you have gas giants

Formation of Terrestrial Planets

Result is small rocky planets with no large gassy outer layers

Accretion of the Inner Planets

Orbital Evolution

This causes: Shifting of the orbits of the Gas Giants

Icy planetesimals ejected to form the Kuiper Belt and Oort cloud

The Final Solar System Our picture of planet formation is driven

by an attempt to explain our own solar system and its three regions Outer or Gas Giant region Trans-Neptunian or Cometary Region

We have also found other types of planetary systems different from our own

Steps in Solar System Formation

1 Inner solar system -- volatiles boil off, resulting in small rocky planets

2 Outer solar system -- large planet cores form rapidly from refractory and icy material, acquire large gas envelopes

3 Edge of solar system -- leftover and ejected icy planetesimals form Kuiper belt and Oort cloud