 For my parents' generation of scientists, there were lots of first missions to new places to be a part of, to be first to Mars and Venus and Jupiter and Saturn and all that. And by the time I got out of graduate school, Pluto was really the only one left. Even though the missions that I've worked on otherwise are great science, it was just irresistible to get on what we used to call the first mission to the last planet. This is Alan Stern, the project leader of the New Horizons mission, which flew by Pluto on July 14, 2015. It marked the first time a vehicle had ever visited the dwarf planet, and nearly a year later, the mission is still giving us crazy amounts of detail about the tiny world at the edge of our solar system. What had we known about Pluto before the mission even got started? I mean, what was the extent of our knowledge? Well, we knew some really interesting things. For example, we knew that Pluto was really a binary planet with a moon half its own size and that there was nothing else like it. We didn't see anywhere else in the solar system, that that system probably formed like the Earth-Moon through a giant impact, which again was super interesting because there's not another analog for the formation of the Earth-Moon system except way out there at Pluto. Pluto is located in a region of the solar system called the Kuiper Belt. It's a big cloud at the edge of our galactic neighborhood filled with tiny icy bodies ranging from the size of Manhattan to the size of whole countries. Scientists used to think Pluto was the only tiny world orbiting beyond Neptune when it was first discovered in 1930 by Clyde Tombaugh. But in the 1990s, researchers started finding more objects and even more dwarf planets in this Kuiper Belt region. It became obvious to planetary scientists, even the whole National Academy, that there was this third class of planet in the solar system and that Pluto was the harbinger of that. Because of Pluto's potential as a destination, a planetary survey in the early 2000s listed the dwarf planet as the number one priority for space exploration among those in the scientific community. The report helped to secure funding for the New Horizons mission, which launched in January 2006. New Horizons was launched on a very, very large expendable launch vehicle in 2006 called an Atlas V. In fact, we bought the most souped up, tricked up version of it you can get with every add-on, every rocket, lightweight nose cone, everything. It ended up being the fastest spacecraft ever launched. We flew it to Jupiter first where Jupiter's gravity gave it a slingshot to make it go even faster so that we could cross the entire solar system in nine years. New Horizons stayed in hibernation mode throughout most of its journey to Pluto, with its last hibernation ending on December 6, 2014, just one month before the spacecraft entered its approach phase in January. That's when things started to get exciting and a bit scary. We had to fly through one little window in space. It was only 60 by 100 miles across and you could not arrive more than nine minutes earlier, nine minutes late after a nine year journey. Somebody did the math and said that that aim is equivalent to hitting a golf ball from LA to New York and landing in a soup can in Manhattan. So we were taking images of Pluto on approach against the star fields and shipping them back to Earth by radio and having teams analyze those to see how far we were off course and to compute engine burn corrections, which we did a series of, to home in and we flew right through that little soup can window. As New Horizons got closer and closer to Pluto, photos taken by the spacecraft showed the dwarf planet in clearer detail. The images revealed the diverse shading and geography of Pluto, as well as the presence of a large heart-shaped region on its surface. Finally, after six months of approaching and one terrifying software glitch, it was time for New Horizons to execute its primary mission. The right word just to say it was emotional. We had put so many years and so much of our lives into that and as much as you practice with ground simulations or with software simulations, as much as we tested it on the ground, it came down to just one day. And at the same time, most of us were pretty exhausted. We'd been working seven days a week and very long days for many weeks on approach because in addition to taking care of the spacecraft and looking under every rock, there was also new data landing all the time and the press was interested in hearing about it, so we had to quickly analyze it. The day of the flyby consisted of two big moments. There was the time of the actual flyby, which occurred at around 7.50 a.m. Eastern time that morning, and then there was the time when the scientists got word back from New Horizons confirming that the flyby actually happened. That signal didn't come until after 9 p.m. There are always unknown unknowns. And New Horizons was traveling so fast that if we'd run into just one little rock pellet in orbit around Pluto the size of a rice grain, it'd be game over and we'd never hear from it again. So in the morning, we all knew the spacecraft had gone by, but because the spacecraft was busy taking data while it was there, it wasn't talking to us until many hours later. And then the signal from the spacecraft took almost five hours to get back to the Earth. So we knew down to the minute when the moment of truth would come, and we were ready for it. And when New Horizons checked in and all the signals were green, it was bedlam. It was awesome. During the flyby, New Horizons took over 450 different observations of the Pluto system. The spacecraft has a big memory bank for storing this data, but a less powerful communication system for sending it all back to Earth. We took a lot of data, but we're sending it back at slow speed, so it takes more than a year for it all to get shipped back to Earth. And even here as we do this interview, we've still got months to go. And there are a lot of goodies up there, and no one knows what discoveries are in it. Every week, new data lands, and we open those packages and see what's inside. And it's been, there's never been a mission really like that. And the data so far has shown Pluto to be something of an anomaly. Actually smaller and smaller worlds have less and less going on, and that's the norm. When you look at, for example, the moons of Saturn and Uranus and Neptune, the bigger ones are a lot more interesting. The smaller ones, the bigger planets tend to be more active than the smaller ones. And then we get to Pluto, and we found, well, there's the exception to the rule. It's every bit as complicated as the Earth or Mars. And on top of it, the thing is active. It should have cooled off by now. It's four billion years on, and it's just roaring with geologic activity and atmospheric activity. Given how much we've learned from New Horizons, Stern says we need to make even more spacecraft just like it. It would be super if we could build a next generation set of missions like New Horizons, three or four more, and fly them to other small planets and sample the diversity of that crazy part of the solar system. We spent dozens of missions going to Mars and Venus, and even Jupiter's up around ten missions now. This is the biggest zone in the solar system, the most populous zone in the solar system. It's where most of the planets lie. They're of this really strange type that Pluto is, and I think they easily deserve several more exploration missions. And for the first time in the multi-million year history of our species, we're kind of stepping out of the cradle right here at the beginning of the 21st century and going out to explore the universe. This is where Star Trek begins. It's awesome.