Currently, there's a race on. Mathematical models suggest that there's another planet out there that's part of our solar system. But, as of yet, it hasn't actually been observed. In The Search for Planet X, you get to join in on that race (at least, vicarously on the tabletop). Who will get the honor of being added to the history books as someone that discovered a new planet? The game is up on Kickstarter now.
From the campaign:
The campaign's up and over its funding goal with 12 days left to go.