The New Horizons spacecraft has been speeding toward Pluto for almost nine years, covering 2.9 billion miles. To conserve energy and general wear and tear, the spacecraft has gone into intermittent hibernation, often for months at a time, slumbering for a total of five years. When sleeping, it was almost completely shut down, maintaining only enough power to send a weekly beep home telling mission controllers that it's doing fine.

But now it's go time.

The spacecraft's systems are programmed to start up again on Dec. 6 at 12:00 p.m. PST/3:00 p.m. EST. An hour and a half later, it will send a signal back to Earth confirming that it's awake. But because it's so far away, it will take more than four hours for the message to reach mission control—around 6:30 p.m. PST/9:30 p.m. EST. Mission controllers will then take six weeks to check all of the spacecraft's systems and prepare its approach toward Pluto, which starts in earnest on January 15, 2015.