The Kuiper Belt is the largest mapped structure in our planetary system, three times as big as all the territory from the sun out to Neptune's orbit.

When I started working with NASA in 1989 as part of a mission to send spacecraft to Pluto, I knew it would take at least 10-15 years to see results of my efforts.

To keep everyone invested in your vision, you have to back up a little bit and really analyze who the different stakeholders are and what they individually respond to.

It's very hard to motivate yourself and others with only one goal - particularly if it's complex and you might not get there until years down the road. That's why intermediate goals are so important.

One thing scientists do is to find order among a large number of facts, and one way to do that across fields as diverse as biology, geology, physics and astronomy is through classification.

Back before the Kuiper Belt was discovered, Pluto did look like a misfit that didn't belong with either the terrestrials or the giant planets.

To say that what a planet is doesn't matter would be to imply that a planetary scientist couldn't explain to someone what the field is about.

Just because Pluto orbits with many other dwarf planets doesn't change what it is, just as whether an object is a mountain or not doesn't depend on whether it's in a group or in isolation.

When we first sent missions to Jupiter, no one expected to find moons that would have active volcanoes. And I could go down a long list of how often I've been surprised by the richness of nature.

We really just didn't realize the diversity of planetary types in our solar system. Pluto looked like a misfit because it was the only one we saw. And just as a Chihuahua is still a dog, these ice dwarfs are still planetary bodies. They're large enough to make themselves round by self gravity, and they surely pass the test of planethood.

I tell public audiences, don't go to a podiatrist for brain surgery; don't go to an astronomer for planetary science.

Liquids may have existed on the surface of Pluto in the past.

People dig exploration.

Why would you listen to an astronomer about a planet?

No one working as an astronomer is shackled in chains. This is a tremendous profession. There are lots of neat people, and you get to do cool things. If I had to say something negative, it's that there's often a whole lot of travel that takes me away from my children. That can be a bummer a lot of times.

I like the planets because they are real places that you can go to and send machines to. Faraway astronomy - galactic astronomy and extra-galactic astronomy - is really cool stuff, but to me, it's about destinations.

We're in the space exploration business, and the outer solar system is a wild, wooly place. We haven't explored it very well.

I actually started my career in planetary science with a master's thesis on Pluto.

New Horizons isn't just visiting Pluto; it's visiting this entire region. Whatever it finds, this will be a signal moment for planetary exploration - the capstone to our first reconnaissance of the planets of our solar system.

I tend to think of Pluto and its moons as presents sitting under a Christmas tree. They're wrapped, and from Earth all we can do is look at the boxes to see whether they're light or heavy, to see if something maybe jiggles a bit inside. We're seeing intriguing things, but we really don't know what's in there.

There are lots of really interesting little planets out there in the Kuiper Belt, but Pluto's the only one that's got all the cool attributes.

One of the implications of the discovery of the Kuiper Belt and its many small planets is that many scientists now think of the solar system as having not two but three zones.

Most of the oceans in the Solar System are deep beneath ice shelves.

Pluto is still active four and a half billion years into its history. It was expected that small planets like Pluto would cool off long ago and not still be showing geological activity. Pluto is, in fact, showing numerous examples of geological activity on a massive scale across the planet.