Sphere by Michael Crichton

From the author of Jurassic Park, Timeline, and Congo comes a psychological thriller about a group of scientists who investigate a spaceship discovered on the ocean floor. In the middle of the South Pacific, a thousand feet below the surface, a huge vessel is unearthed. Rushed to the scene is a team of American scientists who descend together into the depths to investigate the astonishing discovery. What they find defies their imaginations and mocks their attempts at logical explanation. It is a spaceship, but apparently it is undamaged by its fall from the sky. And, most startling, it appears to be at least three hundred years old, containing a terrifying and destructive force that must be controlled at all costs.