How did the Solar System form? Is our solar system unique? Are there other Earth-like planets, or are we a fluke? Under what conditions can Earth-like planets form? Is life common or rare?

Ways to Find Out Look at our own solar system, and think about how it might have formed Look at other solar systems while they form Look for and study other solar systems Create computer models and see if you can produce a solar system

Ways to Find Out Look at our own solar system, and think about how it might have formed Look at other solar systems while they form Look for and study other solar systems Create computer models and see if you can produce a solar system

Solar System Geometry Terrestrial planets closer than gas/water giants Planets get smaller beyond Jupiter Most planets orbit in the same plane Some small bodies are tilted

Summary of Planetary Interiors

Summary (Things a formation theory must explain) The sun, with most of the system mass Giant planets with solid cores (far from sun) Terrestrial planets (close to sun) Most planets orbit in a flat plane Many planets have moons

Our theory Solar system formation begins because of gravity - most stuff ends up in the sun A disk is formed because of rotation Planet cores form in the disk because rocks hit and/or gravitationally attract each other If there’s ice around (> 5 AU from the star, where it’s cold) the cores are bigger. If big enough, they’ll suck gas out of the disk and form giant planets Moons form via collision or capture or in mini disks

Why might material in clouds collapse to form stars? What force keeps clouds from collapsing?

Why might material in clouds collapse to form stars? What force keeps clouds from collapsing? gas pressure pushes out (like in a balloon)

Why might material in clouds collapse to form stars? What force helps clouds collapse?

Why might material in clouds collapse to form stars? What force helps clouds collapse? gravity pulls inwards

If the cloud is big and cold, gravity will win out and the cloud will collapse. gravity pulls inwards

The cloud is spinning. What happens as it collapses? (Think of the water in your bathtub drain) gravity pulls inwards

The cloud spins faster and faster, until it can’t support itself, and flattens out (think pizza dough)

Lucky for us, this is the perfect way to form a solar system. blob = future sun disk = future solar system

Formation basics

Ways to Find Out Look at our own solar system, and think about how it might have formed Look at other solar systems while they form Look for and study other solar systems Create computer models and see if you can produce a solar system

Stars form in Dense Clouds of Dust and Gas What do we mean by dust? What do we mean by gas?

The Orion Nebula

Disks really exist!

Young stars have asteroid belts and Kuiper belts but notice how much bigger this is than the solar system!

In reality, disks are very hard to image. Why do you think this is?

In reality, disks are very hard to image. Why do you think this is? So we usually use spectroscopy to study disks. Here ’ s what stars look like with a spectrograph. What would it look like with a disk around it?

In reality, disks are very hard to image. Why do you think this is? So we usually use spectroscopy to study disks. Disks produce infrared light (just like planets) Here ’ s what stars look like with a spectrograph. What would it look like with a disk around it?

Our theory: What do we think now? Solar system formation begins because of gravity - most stuff ends up in the sun A disk is formed because of rotation Planet cores form in the disk because rocks hit and/or gravitationally attract each other If there’s ice around (> 5 AU from the star, where it’s cold) the cores are bigger. If big enough, they’ll suck gas out of the disk and form giant planets Moons form via collision or capture or in mini disks

Ways to Find Out Look at our own solar system, and think about how it might have formed Look at other solar systems while they form Look for and study other solar systems Create computer models and see if you can produce a solar system

Ways to Find Out Look at our own solar system, and think about how it might have formed Look at other solar systems while they form Look for and study other solar systems Create computer models and see if you can produce a solar system

Ways to Find Out Look at our own solar system, and think about how it might have formed Look at other solar systems while they form Look for and study other solar systems Create computer models and see if you can produce a solar system

Our theory: What do we think now? Solar system formation begins because of gravity - most stuff ends up in the sun A disk is formed because of rotation Planet cores form in the disk because rocks hit and/or gravitationally attract each other If there’s ice around (> 5 AU from the star, where it’s cold) the cores are bigger. If big enough, they’ll suck gas out of the disk and form giant planets Moons form via collision or capture or in mini disks

Why can’t we make a huge computer simulation to explain everything? How do you design a computer simulation?

What models would you create?

A model of planets growing in a disk.

Some things we ’ ve learned from models: Our basic theory holds up pretty well, but... It ’ s hard to get little particles to stick to each other when they collide. It takes a really, really long time to make planets (maybe too long??) It ’ s hard to form planetary systems as flat as ours.

Solar System Formation: Take-away messages Solar system formation begins because of gravity - most stuff ends up in the sun A disk is formed because of rotation Planet cores form in the disk because rocks hit and/or gravitationally attract each other If there’s ice around (> 5 AU from the star, where it’s cold) the cores are bigger. If big enough, they’ll suck gas out of the disk and form giant planets Moons form via collision or capture or in mini disks Theory: Observations generally agree with theory, but it’s hard to see details. They also show us that stars and disks are all very different from each other. And, they gave us the surprising observation of outflows. Simulations also agree with theory, but they can’t model everything at once, and there are some problems (things take too long, for one)

Is our solar system unique? Are there other Earth-like planets, or are we a fluke? Under what conditions can Earth-like planets form? Is life common or rare?