Then Again, Maybe Not
Of course, none of these predictions may be accurate at all. In 2011, as NASA's Dawn spacecraft slipped into orbit around the asteroid Vesta, Laskar checked out the chaotic interactions between Vesta and fellow asteroid Ceres, and between the two large asteroids and the planets. What he concluded was that the interactions between Vesta and Ceres will quickly amplify even the tiniest of measurement errors, making it impossible to predict planetary orbits -- and threats of collisions -- beyond 60 million years into the future [source: Shiga]. While collisions between Vesta and Ceres seem likely in these scenarios, what happens to the planets is uncertain at best.
So, what does this seemingly contradictory information mean? First, the solar system is filled with lots of stuff and that all of these objects, in accordance with Newton's laws, exert forces on one another. Second, these forces can change planetary orbits --a lot -- even if we can't measure those changes over the history of humanity. Finally, and this one is kind of fun, the universe doesn't spawn (or destroy) worlds peacefully, but really, really violently.
In fact, astronomers have evidence of other solar systems self-destructing. In 2008, a team from the Harvard-Smithsonian Center for Astrophysics spotted a Saturn-sized planet orbiting a star in the constellation Centaurus that was giving off way too much heat for its size. The scientists believe now that the large planet is still radiating massive amounts of heat resulting from a collision with a Uranus-sized protoplanet in that star system's recent past.
In 2009, NASA's Spitzer Space Telescope spotted the aftermath of a great mashup between an object the size of our moon and another the size of Mercury about 100 light-years away in the constellation Pavo (the peacock). Instruments on Spitzer detected the telltale signatures of amorphous silica, a substance that forms on Earth when meteorites slam into the ground.
Even if our solar system doesn't succumb to orbital chaos and a billiardlike crashing of the inner planets, we may not be headed to a happy ending. In 5 billion years, when the sun exhausts its fuel supply, our warm, wonderful corner of the universe will start to get pretty uncomfortable. Not long after that, we'll disappear into the belly of our rapidly expanding star and be swallowed whole. Either way, chaos-induced collision or stellar death, our tiny blue world won't go out with a whimper, but with a bang.