10¹⁵ meters = 1,000,000,000,000 kilometers

Now the sun is but a bright dot among other stars. You have entered the region of the Oort Cloud. This is the remnant of the original cloud of dust and gas that formed our solar system.

In the five billion years since it first came together, that dust and gas has slowly been building itself into deep-frozen comet cores, probably billions of them! But they're all much too far away to be seen with any telescope we've built yet.

Once in a very long while, a passing star—or other disturbance in the force . . . of gravity!—jostles a comet core loose and sends it on a trajectory towards the sun.

As these so-called non-periodic comets move toward the sun, they pick up speed and can enter the region of the planets traveling at incredible speeds!

Worse, they can hit a planet (like Earth) moving in a direction opposite to the planet's motion around the sun and add the planet's speed to the force of the impact.

All this makes them very dangerous characters, indeed, and very difficult to predict because, although they may actually be periodic, their orbital period may be more than one million years!