Destiny

From the introduction:

Humanity is not alone in the universe. We at last learned this long ago, when a strange sphere was seen entering the Martian atmosphere, traversing with apparent purpose along its surface. The mission sent to investigate made contact with a miracle. The Traveler. A marvelous being of Light and technology that came to us through the Void, and brought knowledge and innovations beyond our wildest dreams. Human lifespan tripled, disease all but eradicated. The solar system was colonized, the inner planets terraformed, even Mercury turned into a vast garden world. We were ushered into a new Golden Age.

But it was not to last.