“Of course Pluto is a planet: It's massive enough to have its shape controlled by gravity rather than material strength, which is the hallmark of planethood.”

“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.”

“Competition-driven innovation and price pressure that commercial practices foster can only make human spaceflight ever more common and U.S. leadership in this domain ever clearer.”

“Of course Pluto is a planet: It's massive enough to have its shape controlled by gravity rather than material strength, which is the hallmark of planethood.”

“A river is a river, independent of whether there are other rivers nearby. In science, we call things what they are based on their attributes, not what they're next to.”

“The big lesson of planetary science is when you do a first reconnaissance of a new kind of object, you should expect the unexpected.”

“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.”

“I'm hopeful that commercial space exploration will takeoff. To really fuel the spaceflight revolution will require an investment of hundreds of billions of dollars a year, and I think that's only going to happen in the commercial sector - if there are large profits to be made.”

“It says something very deep about humans and our society, something very good about us, that we've invested our time and treasure in building a machine that can fly across three billion miles of space to explore the Pluto system.”

“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.”

“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.”