I read a book a few years ago that looked like a mass-market paperback from the 1990s or so.
It was about humans just barely colonizing our own solar system and doing wormhole experiments around Pluto/Uranus. When their experiment worked, it sent a signal to an alien rock/machine race across the galaxy, who then all warped to Saturn or something and started invading. The Moon had one of the aliens inside its core, hibernating, and when it woke up, it teleported to the aliens' home galaxy, along with a human ship that was orbiting the Moon.
It was written much like a disaster film from the '70s, with lots of characters, cutting back between scenes. It also ended on a cliffhanger; were there ever sequels made? What was the title?