Probability Moon (The Probability Trilogy #1)

Blurb

Probability Moon is a 2000 science fiction novel by Nancy Kress.
The novel concerns a xenological expedition to the planet World, where aliens live who have developed a strange form of telepathy or collective unconscious, "shared reality", which causes piercing "head-pain" whenever "Worlders" attempt to hold strongly differing opinions. Simultaneously, an artificial satellite is found in orbit of the planet which has uncharted powers, and may be the key to winning a war against a xenocidal alien race, the "Fallers."