The Engines of God (The Academy, #1)

Two hundred years ago, humans made a stunning discovery in the far reaches of the solar system: a huge statue of an alien creature, with an inscription that defied all efforts at translation. Now, as faster-than-light drive opens the stars to exploration, humans are finding other relics of the race they call the Monument-Makers - each different, and each heartbreakingly beautiful. But except for a set of footprints on Jupiter's moon Iapetus, there is no trace of the enigmatic race that has left them behind. Then a team of scientists working on a dead world discover an ominous new image of the Monument-Makers. Somehow it all fits with other lost civilizations, and possibly with Earth's own future. And distant past. But Earth itself is on the brink of ecological disaster - there is no time to search for answers. Even to a question that may hold the key to survival for the entire human race...