"Usurper of the Sun" by Housuke Nojiri
Another Japanese novel published here in the US by Haikasoru, which has become one of my favorite publishers in a very short time.
Aki Shiraishi is a high school student in an astronomy club viewing a solar transit of Mercury, when she sees a tower that is being built on Mercury. Using nano technology, it appears that an alien race (dubbed "Builders") are constructing a ring around the sun. The ring eventually threatens Earth's ecology due to it's shadow. Aki pursues a career in the sciences, and travels to the Ring and eventually must confront the Builders as their starship enters the Solar System.
This is truly a hard SF novel. There's very little unrealistic technology development here. Nojiri has thought about alien intelligence, and come up with a clever twist. It somewhat reminds me of Peter Watts' "Blindsight", though not quite as depressing.
It also reads very easily, so I guess that's a tribute to the translator?