Abaddons Gate - James S A Corey (Book 3 of the Expanse)

For generations, the solar system - Mars, the Moon, the Asteroid Belt - was humanity's great frontier. Until now.

The alien artefact working through its program under the clouds of Venus has emerged to build a massive structure outside the orbit of Uranus: a gate that leads into a starless dark. Jim Holden and the crew of the Rocinante are part of a vast flotilla of scientific and military ships going out to examine the artefact. But behind the scenes, a complex plot is unfolding, with the destruction of Holden at its core.

As the emissaries of the human race try to find whether the gate is an opportunity or a threat, the greatest danger is the one they brought with them.