DS: Before we get started, at the risk of bringing up a touchy subject, is Pluto a planet?
Alan Stern: You know, when I first began studying planetary astronomy, the solar system was neatly divided up into four gas giants like Jupiter and Saturn, and four rocky, terrestrial planets like the Earth and Mars. And then there was the lone oddball, Pluto. But that’s all changed, completely. We now know there are many of worlds like Pluto, maybe hundreds, maybe thousands. Pluto and its cohorts are likely to have a differentiated core and mantle, they have geology, atmospheres, polar caps in some cases, and even clouds we believe. They also have seasons, where material phase changes may occur on or below the surface. In every respect they look and behave like the other planets -- they are just smaller, sort of like a Chihuahua is just a small kind of dog -- but a dog nonetheless. Planets like Pluto are small by planetary standards, but that still means hundreds to thousands of kilometers across. So in our solar system and almost certainly others, Pluto-like planets are the norm, not the oddball -- heck, it looks like our old notions are turned on their heads -- it’s planets like Earth that are the oddballs.
DS: New Horizons will cost about 700 million dollars. Not exactly spare change, but still significantly cheaper than a lot of missions to much nearer objects. How was this accomplished?
AS: With careful planning to control the scope of the mission, and a team that cared to keep it on schedule and very close on cost by space standards. Several previous Pluto mission concepts had been canceled owing to cost overruns. We vowed to not let that happen to us.
I had a small, dedicated team, and we approached the project by focusing on making our spacecraft every bit as good as it had to be, but no more, and as simple and light as possible. I determined there would be a suite of just three essential core instruments and four supplemental ones. And I decided that any of those other four would be cut if we were going to go over budget. In the end, our spacecraft and instruments came in within our budget, though our rocket and our nuclear power supply cost more than we wanted. And we launched it right on time and I think we showed that outer planet missions do not have to cost billions as in the past -- I think we broke the mold!
DS: Given the gloomy economic environment, what would you say to taxpayers who ask what they’re getting for that kind of money?
AS: I’d say they are getting a lot. Jobs for starters -- and good, high tech ones at that. Even though we did this mission at a lower cost than some past and future planned missions, it still meant many jobs for spacecraft and scientific instrument designers, engineers, technicians, scientists, and on and on.
But more importantly: we are expanding human knowledge to the edge of our solar system. This is what great nations do -- they make great history. And New Horizons will be a landmark event in that history -- the first exploration of a whole new class of planets and the Kuiper Belt at the very frontier of our solar system. Years from now, when today’s economic problems are forgotten, when the rock stars and movie stars of today are too, when even the day’s politicians are hardly remembered, a student or teacher anywhere in the world who opens a textbook and sees Pluto or Kuiper Belt Objects, will be looking at images and data from New Horizons. I think that’s worth a lot, because it is a legacy for our nation and our civilization.
DS: It'll be moving at quite a clip when it and if it reaches Pluto, how long will the encounter last?
AS: We planned ahead; we didn’t want a ‘weekend at Pluto’ kind of a mission. But since we’ll be moving about 14 kilometers a second when nearing Pluto’s orbit and Pluto will be orbiting at about 5 km/s roughly across our line of motion, we had to design our instruments to allow us to study the Pluto system for months on approach -- which means being able to start their studies at very great range. So we had to pick the right kind of cameras and other instruments, with the right kind of focal lengths and other properties. And we did that! So as a result, we’ll be studying the Pluto system for months and months on approach.
In late 2014, we will be able to finally resolve Pluto as a disk. But the resolution improves geometrically from there. The real fun starts in the spring of 2015, when we sort of open the big shutters and start collecting images better than anything we have now—even from the Hubble Space Telescope’. Finally, on July 14th, 2015, we sail right through the Plutonian system, inside of the orbit of its largest satellite Charon. We’ll also map and study two other, smaller moons of Pluto, Hydra and Nix, during this time. Then we’ll be capturing more images and data on the way out. So the actual observation period will be almost 6 months.
DS: After Pluto, is there enough power to visit any other object and if so, what would it be?
AS: Yes, we have the power and fuel to at least visit one or two ancient Kuiper Belt Objects. We haven’t settled on which ones yet because it makes more sense to wait and see how many more are discovered. There are an estimated 150,000 to choose from, though our fuel supply is limiting us to just a couple along our path after Pluto! Some of them might be more interesting than others. But we don’t want to choose which ones we’ll visit and study now because we will know so much more, we’ll therefore have better informed choices by 2015. Of course, NASA will have to approve funding beyond the Pluto encounter. I hope they will.
DS: So New Horizons, like both Voyagers, will leave the solar system, what happens to it then?
AS: It won’t be moving quite as fast as the Voyagers after Pluto; New Horizons only had the one gravity assist, from Jupiter, but the Voyagers each had two or more gas giant flyby's, so they are moving faster now and we will never catch up with them. But yeah, our spacecraft is moving plenty fast enough to leave the solar system -- it’s headed to the stars!
You know, that's one of the most amazing things I thought about, when I would look at it in final assembly in the clean room, I thought about how long this bird will be flying through the galaxy. It’s not just that it will outlive corporations or nations, or even human civilization as we know it. New Horizons will outlive mountain ranges, it will outlive the earth and the sun. It may very well go on, until the stars burn out; until the protons making it up decay or until the end of time, if there is one. Amazing, isn’t it. What human beings can build?.
DR. Alan Stern is the principal investigator of the New Horizons mission to Pluto and a former Associate Administrator of NASA, responsible for its Science Mission Directorate. This interview was conducted by phone and represents my notes and recollections of his responses. Any errors are solely mine. Dr. Stern may be available, time permitting, to respond to a few questions in comments below.