Will orbital chaos cause Earth, Venus and Mars to collide?

To answer that question, you would need to account for the movements of all the planets, as well as all of the forces being exerted as that movement occurs. Then you'd need to let the solar system run, like a clock, so that the planets cycled through hundreds of thousands of orbits. As this occurred, you would need to track key data about each planet. One of the most important pieces of data to collect would be orbital eccentricity -- the measure of how far a planet deviates from a perfectly circular shape -- because eccentricity determines whether two planets occupy the same airspace and run the risk of having a close encounter.

Think you would be able to run such a simulation in your head or with a desktop model of the solar system? Probably not. A supercomputer can though, which is why Laskar and Gastineau selected the JADE supercomputer to do their heavy lifting. Their inputs consisted of 2,501 orbital scenarios, where each one altered Mercury's orbit by just a few millimeters [source: Laskar and Gastineau]. They chose Mercury because, as the runt of the solar system, it's the biggest pushover and because its orbit synchronizes with Jupiter's to create changes that ripple across the entire solar system.

For each hypothetical scenario, they tracked the motion of all planets for more than 5 billion years (the estimated life span of the sun), letting the computer make all of the complex calculations. Even with the high-powered CPU in the JADE unit, each solution required four months of computing to generate results.

Luckily for life on Earth, the solar system remains stable in 99 percent of the French pair's scenarios -- no planets get set on collision courses or get ejected from their orbits [source: Laskar and Gastineau]. But in 1 percent of them, where the orbital chaos has the greatest cumulative effect, Mercury's orbit becomes eccentric enough to cause catastrophic changes in the solar system. Some of those catastrophes only involve Mercury, which could either crash into the sun or get dislodged from its orbit and flung out into space. But other, more troubling scenarios play out with Earth colliding into either Mars or Venus. A collision with Venus would occur through five steps, all of which illustrate the cumulative effects of orbital chaos [source: Laskar and Gastineau]:

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.

Writing this made me think of a phrase I often read when I was a kid: "the clockwork precision of the universe." Apparently, the universe isn't running with the quiet regularity of a sweeping second hand. As space telescopes and supercomputers look across the cosmos and far into the future, we're finding an unsettled, uncertain universe. But don't stop paying your taxes just yet -- it seems the Internal Revenue Service won't be going away anytime soon.

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