If you're like most people, you've probably grown up with the idea that Earth has only one moon. Do we need another? Well, we might not have any choice if York astronomy professor Kim Innanen's hunches are right.

    Innanen's work on the stability of the solar system has revealed an unusual new kind of orbit around Earth. "We're calling it a 'quasi-satellite' orbit," says Innanen who has been working on the project with astronomy professor Seppo Mikkola of Finland's Turku University. The new orbit was discovered through computer simulation.

    If the second moon exists, it orbits Earth in a kind of a distorted ellipse. Unlike the moon's 28-day orbit, however, Earth's second moon would take an entire year to circle us. So why haven't we discovered it yet? Innanen says people wouldn't be looking for anything there, and even if they found something, they wouldn't realize what they were seeing.

    "We need to search carefully to see if there are other natural objects in the orbit. If it turns out there aren't, we may be able to find other practical uses for it -- like putting a space station there," Innanen says. Any search would take at least two or three years.