So, @MauriceBroaddus' "Sweep of Stars", the first volume in a trilogy of Space Opera.
It builds a world somewhat similar that the one of #TheExpanse - an impoverished Earth, inhabited Moon, Mars, and Titan, mining in the Asteroid Belt and an alien-made portal object (in this case, a wormhole) on the solar system's edge.
The culture inhabiting Moon, parts of Mars and Titan, however, is /very/ different and its development is at the heart of the novel.
(1/n)