Aliens are in the solar system and headed for Venus. They completely ignore Earth and humans, and when some contact is finally established their message is basically saying to leave them alone and they won’t harm Earth.

Of course humans being humans can’t handle their curiosity, so even though several unmanned probes come back destroyed, a manned expedition is still sent to see what the aliens are up to at Venus.

What they find can best described as a giant hoop that is cutting Venus in half like a cheese string cutter. They get too close to the thing and most of the story is dealing with engineering and physics problem solving.

This is proper hard sf complete with diagrams and math equations. I don’t believe you need any special knowledge on physics to get the story, but a certain interest in these kinds of thought experiment stories is probably required. I can appreciate these kinds of stories, Greg Egan is a master in it, but there needs to be more than just the problem and the weird physics thought experiment. The protagonist has an interesting AI assistent that helps him on the way, but other than that, it feels like the story mostly exist for the author to play around with a fun physics problem.

Read in The 1990 Annual World’s Best SF
Originally published in Amazing Stories, March 1989
Rating: 2+