An image of Pluto

This high-resolution image of Pluto was captured by NASA’s New Horizons spacecraft combines blue, red and infrared images taken by the Ralph/Multispectral Visual Imaging Camera (MVIC). Photo Courtesy of NASA.

Q&A with Alan Stern

Chasing New Horizons book cover

Alan Stern (PhD Astro’89) leads NASA’s New Horizons mission, which successfully sent a spacecraft of that name on a multi-billion-mile journey to Pluto and beyond. Stern and co-author David Grinspoon recently published a book about the endeavor, Chasing New Horizons: Inside The Epic First Mission to Pluto (Picador 2018). Here Stern talks about where the spacecraft is, what scientists have learned so far and dinner in London with the lead guitarist for the band Queen — an astrophysicist.


What's your best guess as to New Horizons’ location right now?

New Horizons is speeding through the Kuiper belt on its way to another fly-by of one of the building blocks of small planets like Pluto. That flyby is on the first of January, 2019. The target is called Ultima Thule, which means ‘beyond the farthest frontier’ in Latin. It will be the farthest exploration of any object in the history of humankind. It's really pretty awesome. This spacecraft, built on Earth, has traveled a little over 4 billion miles now, and it's covering almost a million miles every day.


We know for sure that it's still intact and operating — how do we know that?

Because the spacecraft communicates with us by radio on a regular basis. Sometimes once a week — when it's hibernating, on Mondays — and when it's in active operations, as often as several times a day.


There are many CU Boulder connections to New Horizons. If you would, talk to us a little bit about some of them. I know you can't list them all.

I'm a CU alum and I lead the project for NASA. It actually got started when I was a senior graduate student in 1988 and ‘89. There are two faculty members who are on our science team, Dr. Fran Bagenal and Dr. Mihály Horányi. And then we have quite a number of people who were CU students, either undergraduate or did their PhD, who work on the project here at SwRI, where I work, or they've moved to other institutions.


Remind me, was there any CU equipment onboard?

One of the seven scientific instruments was built at the University of Colorado. It's a dust impact detector called SDC for student dust counter. It is actually the first ever student-built instrument to fly on any NASA planetary mission. There were skeptics when we first proposed it, but it worked out so well that now virtually every mission that NASA flies to the planets includes a student-built instrument.


What did you want to accomplish in the book that maybe hadn't been accomplished by thousands of news stories?

David and I and our editors at Picador wanted Chasing New Horizons to really tell the whole inside story. We wanted people to understand how difficult it was to get this project up on its feet. How tough the competition was to win it. How much intrigue there was…


...including competition from one of your own professors?



Intense competition, right?

Absolutely. The two finalist teams were our team and another team based at CU. That's a whole other story. But in our book we wanted to tell the whole story of how this came to happen, how much work went into it, how much persistence it took, some of the intrigue, and really tell a story of what it takes to build a spacecraft, to fly it across the solar system. And put it all in one place. So that people could see the sweep of the whole story of this epic exploration.

Did the process of writing a book, for you, lead to any new realizations about the mission or about Pluto or shadings on things that you had maybe observed but not fully processed?

This is going to sound lame, but the answer, I think, is no, in any significant way. When you live with it for 26 years, you’ve thought about it a lot. But part of the reason I'm saying no is I know that your follow up question would be, ‘Like, what?’ And I can't think of a single thing.

However, there's a second side to that: I'm getting questions that I've never been asked before, even though I've been talking to the media about New Horizons since the day we won the project. And the question you just asked is an example — I've never been asked that question.


For you, what's the most significant thing that we've learned about Pluto from New Horizons mission? If you're going to narrow it down to one thing you've learned so far, what's the big thing?

Alan stern and team looking at photos of pluto

Alan Stern, center, and New Horizons team view some of the first photos of Pluto on July 14, 2015. Photo courtesy of NASA.

I have been asked that question before…


I'm sure.

And there is no one thing. There are two things that at the very top. And I can put everything else under those two. The first discovery is just how complicated Pluto itself is. Usually in planetary science, smaller bodies are simpler. But Pluto way bucks that trend. It's as complicated as the Earth or Mars. Now, realize Pluto is about the size of the continental United States, and there's a lot of geologic variety in the United States. But what we saw in Pluto just knocked our socks off — glaciers and mountain ranges and a complicated atmosphere with complicated weather and young areas and old areas and tectonics and avalanches. It's snowing there. I could go on and on. We see dynamics in the geology, and we see young surface features that are very large. There are volcanoes the size of Mauna Loa on this tiny little planet, and there are completely different surface compositions from one place to the other. It really rewrote the textbook on how complicated small planets can be.


Okay, so that's one of the big ones.

The other was that we found lots of signs of a geological activity on a vast scale. A common geophysical paradigm is that smaller worlds cool off quicker than big ones. Just like a cup of coffee will cool off a lot quicker than a vat of coffee. Pluto has somehow managed to be massively geologically active four billion years after formation. And we're not sure why.


That's true of Earth too, isn't it?

It is true of Earth, but the Earth is much larger.

So, for example, Pluto’s big satellite, Charon, is half Pluto’s size, and every place we look on its surface is very old. Because that engine ran out 4 billion years ago. As an aside, the way that we get the ages, we count the number of craters per square kilometer. It's the same idea as if it's raining outside and you run outside with a piece of paper: The longer it's out there, the more dots on a piece of paper. But on Pluto we find places like the big glacier called Sputnik is a million square kilometers — it's the size of Texas and Oklahoma combined — yet we can't find a single crater, which means it was born yesterday. Similarly, on Pluto’s largest volcanic feature — itself the size of Mauna Loa in Hawaii — we have a crater expert who thinks she found one crater. The point is, that 15,000-foot tall massif, that caldera, has been erupting in the recent past.


So that's going to provide a lot of fodder for continued study.

We want to go back with an orbiter.


What's a fun thing that we learned about Pluto that might not be scientifically all that interesting, but just kind of makes you go, ‘wow.’

Oh, that's easy. It's the heart. It's the little planet with a big heart.

New Horizons journey info graphic

And remind us, the heart-shaped region visible on Pluto’s surface in photographs represents what?

The western side is the giant glacier I was talking about, called Sputnik. The eastern side, we're not sure. To some of the photo geologists it looks like it’s windblown material that's come off the glacier and just happens to be distributed that way.


In general terms, who's doing what with all of the data that has already been transmitted back?

All the data from the Pluto Flyby is on Earth. It took a long time, but we sent it all back: 460-something separate scientific observations by seven instruments looking at Pluto and each of its five moons. All that data is not only on the Earth, we've archived it in NASA's planetary data system, which is open for anybody to use, anybody, anywhere.


Is there any consensus among those of you who are most closely tied to this about what the most burning question is, based on the information that you now have?

If you asked 25 of us, I bet you’d get 25 different answers. But also, I think you'd find some common themes, like: How is it active after 4 billion years? What's driving that energy source? Why is it so complicated? How did its satellite system form? And there are some big questions beyond that. For example, there's a whole set of discoveries about features on the surface that looked like liquids or slurries flowed or ponded in lakes on Pluto. They look like frozen lakes. But you can't have that on Pluto. It's too cold and the atmospheric pressure is too low to allow liquids to run. That's telling us probably that in the ancient past, Pluto had a much thicker atmosphere. Where did it go? Does it come and go, or was it just there once? How long was it there? We're just stunned — it's like a kid who is overwhelmed with their presents on Christmas morning. And all year long. And here we are, going on three years after the flyby, and feeling like we've got years of work to do just to make sense out of the flyby data, much less what we can do with more.


Do you talk much to Michael Brown from Caltech, [author of How I Killed Pluto and Why It Had It Coming]?

I'm on another science team with him. I know Mike very well. We completely disagree on this issue of what planets are, but otherwise we are colleagues.


That was going to be my next question: Do you agree with him, that Pluto isn't a true planet?

I don’t agree. In fact, most planetary scientists disagree with Mike. I realize Mike has a book, and he wants it to sell, too, so he gave it a very clever name. But it's just the case that planetary scientists consider these small planets, planets. We call them dwarf planets, but the sun is a dwarf star — does that make it not a star? And dwarf galaxies are galaxies — that's a term in astronomy.

The very simplest test you can tell your readers about is what I call “the Star Trek test.” And we all watch Star Trek from time to time, and they show up somewhere every episode and they turn on the viewfinder on the bridge. In about a second, the audience at home knows whether it's at a planet or if they're orbiting a comet or an asteroid or an alien spacecraft or some nebulous space or whatever. And that's really a pretty good test: If Pluto came up on the viewfinder of the bridge of the Enterprise or any other Star Trek vehicle, people would say, ‘Oh, we're orbiting a planet.’


I gather that Brian May, the guitarist for Queen and also an astrophysicist, took a real interest in New Horizons.

He did. In fact, He's got a blurb on the back of Chasing New Horizons.


Did he spend some time with you?

Yes, Brian came to the flyby. We made him an official collaborator. He has come to several scientific meetings. He's come here to Boulder. I saw him once in London for dinner, and we go to this little vegan restaurant in the West End, and he pulls out his laptop and he's got data. He's been working on it…


New Horizons data!

New Horizons data! He pulled that laptop out — it's Friday night about 9:00 — and I said, ‘Hey, I didn't bring any weapons to this table. I came unarmed.’ But he's a very serious guy about his science in addition to being very talented and successful musician.


So what's next for you? I mean, how do you top something like this?

I don't know that I have to top it. I don't look at it that way. I work on a lot of scientific missions, and I've got three kids and lots of things to do. When I was a kid, all I wanted to grow up, be involved in space exploration, I wanted to really make a contribution, to be a part of things that were important. And with New Horizons, I know we truly did.

A lot of people harp about ‘This is not America's greatest time.’ You know, ‘Great things happened in the past, but we're not really on our game.’ New Horizons is an example of this country exactly on its game, doing something historic that all the world could see.


Condensed and edited for length and clarity.

Read more about NASA's voyage to Pluto in the Coloradan.