Eon

The 21st century was on the brink of nuclear confrontation when the 300 kilometer-long stone flashed out of nothingness and into Earth's orbit. NASA, NATO, and the UN sent explorers to the asteroid's surface...and discovered marvels and mysteries to drive researchers mad.
For the Stone was from space--but perhaps not "our "space; it came from the future--but perhaps not "our" future; and within the hollowed asteroid was Thistledown. The remains of a vanished civilization. A "human"--English, Russian, and Chinese-speaking--civilization. Seven vast chambers containing forests, lakes, rivers, hanging cities...
And museums describing the Death; the catastrophic war that was about to occur; the horror and the long winter that would follow. But while scientists and politicians bickered about how to use the information to stop the Death, the Stone yielded a secret that made even Earth's survival pale into insignificance.
Greg Bear was born in San Diego in 1951. His father was in the navy, and by the time Greg was twelve years old, he had traveled with his parents to Japan, the Philippines, and various parts of the United States. He is the author of over twenty books, which have been translated into a dozen languages. He has won four Nebulas and two Hugos for his SF writing and was awarded the 2006 Robert A. Heinlein Award for outstanding published work in hard science fiction or technical writings inspiring the human exploration of space. In this novel, Bear offers what "may be the best constructed hard SF epic yet" ("The Washington Post").
The 21st century was on the brink of nuclear confrontation when a 300-kilometer-long stone flashed out of nothingness and into Earth's orbit. NASA, NATO, and the UN sent explorers to the asteroid's surface. They discovered enough marvels and mysteries to drive all researchers mad.
The strange Stone was from space--but perhaps not "our "space; it came from the future--but perhaps not "our" future. Within the hollowed asteroid was Thistledown, the telling remains of a vanished civilization. Indeed, a "human" civilization--English, Russian, and Chinese-speaking--with seven vast chambers containing forests, lakes, rivers, and hanging cities.
Thistledown also contained museums describing the Death; the catastrophic war that was about to occur; the horror and the long winter that would follow. But while scientists and politicians bickered about how to use the information to stop the approaching Death, the Stone yielded a secret that made even Earth's survival pale into insignificance.
"Sharing aspects of Clarke's "Rendevouz with Rama," this novel's] uniqueness arises from Bear's bold imagination. Bear is a writer of passionate vision." Eon "is his grandest work yet."--"Locus"