New Horizons left Earth nearly 9 years ago, and the craft has spent almost two-thirds of that time in one of 18 hibernation periods designed to keep its systems operational. But even though wake-ups have become routine, this one was special: It's the last time the spacecraft needs to wake up before it gets to Pluto.
And what will it find there? We just don't know, and that's the most exciting part. The mission's principal investigator Alan Stern of the Southwest Research Institute has said that New Horizons will radicalize our knowledge of Pluto in the way that Mariner 4's flyby in 1965 changed our view of Mars.
For reference: Many people assumed that Mars was lush and full of water and life before that flyby, and were surprised to see the cold, red planet we now know well.
Pluto may have lost its full-fledged planetary status in recent years, but it has just as many secrets to reveal to NASA as the rest of the solar system's bodies.
The real excitement will start on Jan. 15, when New Horizons gets close enough to Pluto to start taking measurements. By mid-May, the spacecraft should send home the best images we've ever had of the dwarf planet. To date, the best we have comes from the Hubble -- and even that powerful telescope shows Pluto as a blurred splotch.
(And why can't the Hubble, which takes beautiful images of far-away galaxies, catch something in our own solar system? Pluto may be much closer than those space objects, but it's also so, so, so much smaller.)
By July, the spacecraft will make its closest approach, coming within just a few thousand miles of the dwarf planet and its moons.
New Horizons will look at the surface and atmospheric compositions of Pluto in the hopes of learning something about dwarf planets in general -- which we now know are more common in the solar system than rocky worlds like our own and gas giants like Jupiter combined.
“New Horizons is on a journey to a new class of planets we’ve never seen, in a place we’ve never been before,” project scientist Hal Weaver said in a statement. “For decades we thought Pluto was this odd little body on the planetary outskirts; now we know it’s really a gateway to an entire region of new worlds in the Kuiper Belt, and New Horizons is going to provide the first close-up look at them.”
Scientists are also excited to study Pluto's largest moon, Charon. The two form a binary planet. Instead of orbiting Pluto, which is about twice its size, Charon circles around a fixed point in tandem with it -- like two ice dancers holding hands and spinning together. This will be our first chance to study a such a system, even though they're not uncommon in the galaxy.
You can read more about NASA's reasons for going to Pluto at the missions website. And we'll keep you updated as New Horizons blinks off its sleep sand and starts doing science.