The wanderer.

All eyes were watching the eclipse of the Moon when the Wanderer--a huge, garishly colored artificial world--emerged. Only a few scientists even suspected its presence, and then, suddenly and silently, it arrived, dwarfing and threatening the Moon and wreaking havoc on Earth's tides and weather. Though the Wanderer is stopping in the solar system only to refuel, its mere presence is catastrophic. A tense, thrilling, and towering achievement. Winner of the Hugo Award for Best SF Novel of the Year!