Beyond the orbit of Neptune lies the Kuiper Belt, a disc-shaped region of space containing the leftover material from the formation of our Solar System some four billion years ago. 20 times as wide and 200 times as massive as the asteroid belt between Mars and Jupiter, it contains countless celestial bodies composed of frozen ices such as water, ammonia and methane. Known as Kuiper Belt objects, they can range in size anywhere from a small rock to over 100 kilometers or more in diameter.
Occasionally, the orbit of a Kuiper Belt object may be disturbed by the gravitational interactions of the giant planets, and cause the object to cross the orbit of Neptune. If one should come close enough to Neptune, it can be attracted by the planet's massive gravitational field and sent on a new course into the inner Solar System, where it will become a comet.
It was believed that only the interaction of planetary gravitational fields, or a collision between two Kuiper Belt objects, could alter the trajectory enough to send one of these proto-comets toward the Earth.
The alien sighed as the red blinking light on his computer indicated yet another negative result. His frustration was compounded by the many months of fruitlessly searching for an object of just the right size and composition. Too small, and it would burn up in Earth's atmosphere before reaching the surface. Too large, and its impact could devastate the planet, threatening the very civilization he was trying to save and dooming the future of not one, but two worlds. The destiny of two civilizations and countless billions of lives all depended on the successful completion of this mission. He shuddered at the enormity of that thought.
Turning back to his controls, he once again reconfigured the ship's sensors and piloted his craft toward the next object, only a few thousand kilometers distant. Suddenly, the computer began to beep, its green indicator light bringing a look of hope to the alien's face. The size of the scanned object appeared to be well within ideal parameters. His hope rising, the computer next performed a spectral analysis of the object. Although the size was correct, if the distribution of its frozen elements was not in the right balance, its trajectory would be flawed and hitting its ultimate target could not be guaranteed. He held his breath as the computer silently completed its analysis. A few moments later it gave him the result he had been hoping for.
Without hesitation, he manuevered his ship closer to the object. Within minutes, he had landed on the icy sphere. Upon contact, robotic grapples attached themselves to the frozen surface of the object, and a high speed drill was deployed which quickly bored through to its icy core. Once the center was reached, a robotic arm placed the alien's priceless technology package deep within the nucleus of the proto-comet. With a touch of a button, he activated the device. Rainbow hues began to emanate from deep within, its coruscating colors shining brightly through to the surface of the proto-comet's translucent body. With another touch of a button, the craft detached from the future comet and manuvered to its opposite side. He then activated a tractor beam and began to slowly accelerate until the critical velocity was reached that would carry the comet to its destination. The alien smiled as he released the tractor beam, allowing the comet to continue on its pre-set course. The automatic tracking and guidance system was now locked in on its target, a small city located on the planet Earth's North American continent.
The alien smiled as he turned his craft for home.