Probability moon

When a new race of aliens stumbles upon the ancient star gates that make interstellar travel possible, humankind sends a team of scientists to study a newly discovered planet populated with an alien society in which everyone agrees on the truth. Humanity has expanded into other solar systems using the remnants of an ancient technology of star gates--instant travel devices left in place by a now-vanished superrace. Yet now an alien race also has discovered the gates, a race with which no communication is possible, and they are determined to exterminate humanity.