The more we learn about neighboring solar systems in our galaxy, the more we realize our own solar system is a bit…odd. And it may all be Jupiter’s fault (but thank goodness for Saturn for saving us all!)
A model for the standard solar system setup
Most solar systems have more planets packed in closer to their sun, and those planets are often larger as well. In nearly 500 systems, we’ve observed a pattern where either gas giants or rocky planets (like Earth or Mercury) are several times larger than Earth, and sitting right next to their local star. It’s now thought that our own solar system also followed this pattern before our current inner planets existed. But that all changed when a young Jupiter went on a bit of a joy-ride and broke everything.
Jupiter’s jaunt smashed planets to junk
Even a young Jupiter was large enough to cause havoc when its orbit became disrupted eon ago, in an event dubbed the “Grand Tack.” It migrated closer to the sun, setting off a gravitational chain reaction for the other, super-Earth-sized planets that were then closer to the sun. These planets are theorized to have then destroyed each other, and the remaining debris was either absorbed by the Sun or came together to form our current inner planets. Jupiter probably grabbed some of these raw materials as well, which may explain why Mars is smaller than Earth, despite having been formed in what would have been a resource-rich location.
Jupiter’s destructive romp was then stopped by Saturn. The second gas giant’s gravity probably pulled Jupiter back away from the sun, switching places with the asteroid belt and stabilizing in its current orbit. Without this influence, Earth and its neighbors wouldn’t have had the space to safely form where they did.
Source: Observe: Jupiter, Wrecking Ball of Early Solar System by Andrew Fazekas, National Geographic