The piddling human lifespan affords mankind a unique sense of security. Since we're only around for about 80 years or so, its hard to comprehend the churning death-box of chaos that is the universe. Take our Solar System. Seems pretty static: everything is out there, just doing laps with comforting regularity of a ninth grade gym class.
Or so it would seem.
Turns out, Ol' Lady Gravity is constantly at work, making subtle changes as the planets exert little tugs on each other. A lot of little tugs eventually add up to some spectacular changes, like Earth colliding with Mars or Mercury. D'oh.
Such a collision would be a game-ender:
In the case of a smash-up with Mars, for example, "all life gets extinguished immediately, and Earth glows at the temperature of a red giant star for about 1000 years", says Gregory Laughlin, a co-author of one of the studies at the University of California in Santa Cruz, US.
The good news is that this probably won't happen for at least 40 million years. Which is bound to irritate the Sun, which was all set to burn Earth to a cinder in 5 billion years. Stupid uppity and/or drunken planets.