Baby solar systems
Baby solar systems
Billions of years ago, our solar system was just a bunch of random gas and dust floating around as a nebula. As it collapsed, it formed a rapidly spinning merry-go-round of a flat disk around the young and hungry proto-sun. Over the course of 100 million years, that disk somehow became the planets and other smaller denizens of our home system.
Computer simulations of the disk-to-planet process are fantastically difficult, due to all the rich and complex physics involved, but they have a few general features. The innermost worlds tend to be small and rocky, while the outermost planets tend to be big and gassy and/or icy. Plus the process of formation leads to a bunch of random junk floating around.
Another general feature is that newborn planets tend to move quickly into resonant motion, meaning that orbits become integer multiples of each other. For example, Mars might orbit four times for every Jupiter orbit, and Jupiter might orbit twice for every turn around the sun that Saturn gets.
And when it comes to our solar system in particular, in simulations the giant planets tend to form much closer together, and much closer to the sun, than they are today.
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