9. Missing Planets

Imagine the surprise of a really smart scientist who runs the latest computer model, loaded with a decades-old, widely accepted theory about how our solar system formed, and the computer spits out a diagram with only seven planets.

Uranus and Neptune have been missing, in theory, for some time now. The problem arises because the standard model of planet formation requires material to crash together and stick over millions of years. Once a large core is built, gas can be attracted to create planets like Jupiter and Saturn. But out where Neptune and Uranus roam, there would never have been enough hard material for this to work.

This year, theorist Alan Boss of the Carnegie Institution of Washington put forth a radical new idea, a planet-formation mechanism that conveniently builds the two outer ice giants, too. Boss figures the four big planets in our solar system did not develop from rocky cores, as the standard model once held, but that they collapsed from large gas and dust clouds.

To round out his theory, and the planets, Boss had to put our fledgling solar system in another part of space. He chose a region of intense star formation, so that the UV radiation from a nearby star could strip Uranus and Neptune down to fighting weight. The solar system then migrated to its present, more pleasant region of the galaxy.

All well and good, but other astronomers are very skeptical. We're left with an old theory that doesn't work and a new one that is, in the words of its creator, a wild idea.

Maybe in 2003, while some scientists are busy looking for planets around other stars, someone will figure out for sure how the planets in our own solar system were created!

Next Page: Can we even survive 2003?