Wherever Seeds May Fall

Astronomers from around the world watch in awe as an extrasolar comet approaches Saturn, being drawn in by its immense gravity. When the comet grazes the planet rather than plunging beneath the clouds, speculation is rife. With the comet now on course to collide with Jupiter, even the most skeptical scientists can no longer deny what's happening—an alien spacecraft has entered the solar system and is using the gas giants to slow its approach to Earth. -Goodreads