I just finished Usurper of the Sun
by Housuke Nojiri - it's about a young girl who's a member of her school's astronomy club, and one day is observing Mercury when she sees what appears to be a tower being constructed on the planet. Eventually, it becomes clear that a ring is being built around the Sun - but by whom? She makes it her life's work to find out, and to learn why, and to try to stop them (because it's big enough that it's blocking sunlight from getting to Earth and adversely affecting the climate).
Now I'm in the mood for a classic, so I started reading The Stars My Destination
by Alfred Bester this morning.