At the far edge of the solar system, a small machine built by human hands has stirred from a year of silence, resuming its quiet vigil at the frontier of everything we have ever called home. NASA's New Horizons spacecraft, now 5.9 billion miles from Earth, awakened this week from a 321-day hibernation to continue its journey toward the heliopause — the boundary where the sun's reach finally surrenders to the interstellar void. It is the second-farthest working spacecraft humanity has ever made, and its instruments are more sensitive than anything that has crossed this territory before. In its