Astronomers looking at the long-term future of the solar system have concluded that "a collision with Mercury or Mars could doom life long before the Sun swells into a red giant and bakes the planet to a crisp in about 5 billion years." USCS astronomers Gregory Laughlin and Konstantin Batygin, and Jacques Laskar of the Observatoire de Paris, ran computer simulations of the solar system. According to the New Scientist,
The studies suggest that the solar system's planets will continue to orbit the Sun stably for at least 40 million years. But after that, they show there is a small but not insignificant chance that things could go terribly awry....[T]here is a 1 to 2% chance that Mercury's orbit will get seriously out of whack within the next 5 billion years.
This would tend to destabilise the whole inner solar system and could lead to a catastrophic collision between Earth and either Mercury or Mars, wiping out any life still present at that time.
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....
In one of Batygin and Laughlin's simulations, Mercury was thrown into the Sun 1.3 billion years from now. In another, Mars was flung out of the solar system after 820 million years, then 40 million years later Mercury and Venus collided.
