The Solar System’s story

For almost two decades my research has focused on understanding how our Solar System came to be. Why does our planetary system look like it does, and why is it so different than most of the exoplanet systems we see? What were the key events that shaped the planets (including delivering Earth its water)? How would our Solar System have turned out if things were just a little bit different?

This blog series will discuss what we know (and don’t know) about the formation and evolution of our Solar System.

I’ll explain the latest thinking on the different pieces of the puzzle. I’ll go pretty deep, but I’ll do my best to make it understandable and interesting. (I’ll treat it like a 20-piece puzzle, not a 1000-piece one.)

There are lots of “Solar System puzzles” out there, but they don’t really put the right pieces together ;).

A satisfying origins story explains how we got where we are now. It describes the landscape. It explains how the central conflict came to be. It describes the hero’s quirks and where those originated (I’m looking at you, whiny Luke Skywalker). And it makes the villain believable and, ideally, relatable.

I’ll guide you through the Solar system’s story, starting from the gas cloud that formed the Sun, to the present-day planets, asteroids and comets, and beyond into the distant future. As you will see, not all scientists agree on every detail of this story, and I’ll explain the pluses and minuses of different ideas.

From my astronomy poem book, Black Holes, Stars, Earth and Mars. Credit: Owen Raymond (yup, he’s my son).

The goal of this story — or of any scientific “model” — is to reproduce what we see. What exactly do we know about our Solar System? Let’s list the most important things:

  • The planets, of course! Specifically, their masses/sizes, orbits and compositions.
  • The asteroids and comets — their orbits and compositions.
  • Meteorites. Analyses of meteorites can tell us about how fast and even where different objects formed, although this is admittedly circumstantial evidence.
  • Astronomical observations. While we can’t take pictures of the Solar System in formation, we can put our Solar System in context by observing how other stars form (also circumstantial).

Science-based ideas about the origin of the Solar System have been thrown around for centuries. In the 18th century, Kant (the bigwig German philosopher) and Laplace (the famous French mathematician) proposed the “nebular hypothesis” — the idea that the Solar System formed from a disk of gas, to explain why the planets all orbit the Sun in nearly the same plane. In the early 20th century, Moulton (an American geologist) and Chamberlin (an American astronomer) proposed the “planetesimal hypothesis” — the idea that the planets were all formed from smaller, asteroid-sized rocky objects.

We now know that both of these ideas were right. Well, sort of. Each is basically a piece of a much larger puzzle.

I’ll break the Solar System’s story into digestible chunks. Some chapters are about specific processes and others try to pin down exactly what happened in our Solar System. Some are mostly about meteorites while others are largely based on astronomical observations, with computer simulations sprinkled throughout.

Below are links to each of the chapters. I will continuously update them as needed to reflect changes in thinking.

Chapter 1: The Sun’s birth cluster and planet-forming disk
Chapter 2: From dust to planetesimals
Chapter 3: From planetesimals to “planetary embryos”
Chapter 4: Orbital migration
Chapter 5: Growth and migration of gas giants
Chapter 6: Formation of the rocky planets: choose your own adventure!
Chapter 6.5: Water delivery and the origin of life on Earth
Chapter 7: The giant planet instability (the “Nice model”)
Chapter 8: The Moon-forming impact and late accretion on the rocky planets
Chapter 9: Asteroids, comets, and dinosaur-killing impacts
Chapter 10: Billion-year evolution of the Solar System: climate forcing and orbital chaos
Chapter 11: The end of the Solar System

Additional resources

  • A 2-lecture series I gave at a summer school in 2021 (with slides nicely incorporated into the background) — part 1, part 2.
  • The MOJO videos (11 short videos about different pieces of the puzzle)
  • A couple of technical review papers about planet formation: downloadable versions here and here.


14 thoughts on “The Solar System’s story

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