Mare Marginis
Nigel meets the Snark, which disables Nigel's conventional weapons and begins talking to him. It says that organic civilizations and species are inherently unstable; they flash brilliantly and commit suicide sooner or later. The autonomous machines they craft live on long after them, going on and evolving. But they cannot truly compete with the organics, who live "in the universe of essences". That is the reason for the Great Silence. Nigel's superiors order him to use the nuclear weapon, but he refuses. They override him and fire it anyway but the Snark flees the Solar System faster than the missile can follow. The decision to fire is covered up, but Nigel blackmails NASA into letting him go to the Moon; the Snark had directed a transmission at Mare Marginis for unknown parties, and Nigel wanted to find those parties.