A manufactured system 
I've read theories suggesting that our solar system could one day fall apart due to a resonance between Jupiter and Mercury causing Mercury's orbit to elongate crossing the orbits of Venus and Earth.
Well, in all honesty, we are toast in several billion years when the sun turns nova. Or when Milkdromada happens. I'm not going to worry.
I'm more worried about some idiot getting a bomb or an Emp or bringing back something like smallpox or Spanish flu and bye bye humanity, or throwing us back to the dark ages.
Out out brief candle? :(
