Is our solar system missing a planet?

Possibly, according to some scientists who are trying to understand the early days of Sol and friends.

One way that researchers study events like the creation of the solar system is to model what might have happened using computer software. The basic idea works like this: We know a decent amount about the physical laws (like gravity) that govern the creation of planets and the formation of a solar system. So scientists can take those laws, and program them into a virtual universe that also includes other real-world data ... like what we know about the make-up of the Sun and the planets orbiting it. Then, they recreate history. Then they do it again. Over and over and over, thousands of times, the scientists witness the creation of our solar system.

It doesn't happen the same way each time. Just like you can get a very different loaf of bread out of multiple attempts and baking the same general recipe. But those recreations start to give us an idea of which scenarios were more likely to have happened, and why. If our solar system tends to form in one way and resist forming in another, we have a stronger basis for assuming that the former way was more likely to be what really happened.

That's what you're seeing in this study, which Charles Q. Choi writes about for Scientific American.

Computer models showing how our solar system formed suggested the planets once gravitationally slung one another across space, only settling into their current orbits over the course of billions of years.

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