When Worlds Collide

In the good old days before physics and maths got all post-modern on us, the solar system ran like clockwork and the trains were always on time. Planets knew their place and wouldn't dream of spinning out of orbit and smacking each other in a Michael Bay-style extravaganza of explosions and mayhem. Unfortunately, standards have since slipped.

Actually, the idea that the planets were stuck in their tracks like some sort of cosmic Scalextric set was in trouble as far back as Newton, who could do the maths to prove the stability of a single planet orbiting the sun but wasn't able to produce a general solution to the problem of the Moon's orbit. Newton believed a general solution for all the planets was impossible and that the long-term stability of the solar system was thanks to God fiddling with the celestial clockwork every so often.

Thanks to computers, we can now run simulations of the solar system for billions of years into the future before tiny unknown forces like the mass lost by the sun due to the solar wind, or the effects of galactic tidal forces make a joke of the numbers. The possible planet-smashing predictions reported by the press are the result of 2500 simulations run by Jaques Laskar and Mickaël Gastineau of the Paris Observatory who in each run simulated the next five billion years of the solar system's future, up until the point where the Sun grows into a red giant and vaporises most of the inner solar system.

The interesting thing to me is what the difference was between each run: They changed the initial position of Mercury by a single metre.

In 20 of their cases, Mercury's orbit eventually went nuts; sometimes falling into the sun, sometimes smacking into Venus. Regardless of how Mercury flew off the rails, the peturbations it caused on other planets was enough to cause some serious orbital shennanigans, including a possible Mars-Earth smackdown of the Hollywood kind.

So, given time, the tiniest planet (Sorry, Clyde) can throw the solar system into disarray. Makes me think of the old joke about the Earth falling into the Sun if everyone in China jumped at the same time. Well, it might not happen right away...

One for Mythbusters, perhaps.

Oooh! I'm quite fat! what if I jump up and down for a really long time? What would happen first; the Earth falls into the Sun, the Sun eats the Earth or I get in shape?