Gravity Assist Podcast: The Kuiper Belt, with Alan Stern, Part 2
The Gravity Assist Podcast is hosted by NASA’s Director of Planetary Science, Jim Green, who each week talks to some of the greatest planetary scientists on the planet, in the process giving a guided tour through the Solar System and beyond. After last week’s chat with Alan Stern, who is New Horizons’ Principal Investigator from the Southwest Research Institute, Stern returns to discuss the next phase of the New Horizons mission, which will be an encounter with an object deep in the Kuiper Belt, called 2014 MU69, on New Year’s Day 2019.
Here’s a short teaser of this week’s podcast:
Jim Green: During the Pluto fly-by we were worried about the safety of our spacecraft as we flew past. Are there similar concerns about debris in the area around MU69?
Alan Stern: Yeah, and we’re worried, primarily, because we’re going so fast. You know, we’re going at ten miles [16 kilometers] per second. So even if you hit something small, it’s a very powerful wallop, and there’s basically no good place to hit New Horizons. Even [something as small as] a rice pellet that hits the spacecraft could cut a fuel line or take out a circuit board or destroy an instrument or what have you. So, we’re trying to certify the path as best we can. The occultations help us with that, because [immediately] before and after the main occultation of the hard body itself, you can look for dips in the light due to rings or other debris structures that could be in orbit. Fortunately, we didn’t find any. So, that tells us that some of the worst disaster scenarios that could be out there aren’t out there at MU69. They might be somewhere else, but they’re not at MU69. But, still, we have to look even harder to certify the path on approach. We’ll do that with our own telescopes on board, and our own cameras on board, by sending that data back to Earth throughout the fall of 2018, and we’ll be scrutinizing those images as best we can. If we find anything that’s concerning, we’ve planned an entire backup fly-by at a greater distance, which is presumably safer, to give ourselves some options for still getting good data, but avoiding danger if it’s in our path for the very closest approach.
Jim Green: One of the things that I always wondered about is that we get comets from very far away in the Oort Cloud, but there’s got to be comets coming out of the Kuiper Belt, too. What do you think the relationship between Pluto-like objects and comets is?
Alan Stern: Well, that’s a really good question. We know that comets, the short-period comets, come from the Kuiper Belt. We’ve seen quite a number of those up close with spacecraft missions; Rosetta recently orbited one for two years, but we had various American and European spacecraft fly by comets, also some old Soviet spacecraft that flew by comets in the 1980s. They don’t look anything like planets. They’re small and lumpy and they don’t have the geological processes that big worlds, like Pluto have.
Alan Stern: Also their composition turns out to be quite different. We see on the surface of Pluto much more exotic ices than we see on the surfaces of comets, things like nitrogen-ice that are very rare in comets. We see a bound atmosphere that we don’t see around comets. So, just like the asteroids and the Earth are different, the comets and the small planets of the Kuiper Belt are very different. But, they’re all teaching us about the origin of the Solar System and about the types of objects we can expect to find around other stars. It’s all part of the basic exploration that we do, as we open up the Solar System to space travel.
Jim Green: After it flies by MU69 on 1 January 2019, New Horizons is heading out of the Solar System. Is it going in the same direction that the Voyager spacecraft are?
Alan Stern: It is going in roughly the same direction as the Voyagers and, like the Voyagers, it will escape out into the Galaxy.
Jim Green: New Horizons has radioisotope power and that will last for a considerable length of time past MU69. Do you think it can make it to the heliopause?
Alan Stern: We have a lot of Kuiper Belt work left to do before we get to the heliopause. The heliopause is probably 100 astronomical units (AU) out [Editor’s note: New Horizons’ fly-by with MU69 will take place 43.3 AU out from the Sun]. If you calculate the amount of power that we have on board, we could still be operating then. It’ll be in the mid-to-late 2030s. The thing about the heliopause is that it ‘breathes’ in and out with the solar cycle, and sometimes it’s further and sometimes it’s closer. Although we can predict exactly where New Horizons will be in any given year, no one knows how to predict [the Sun’s activity at any given time]. So, it’s hard to know whether in the 2030s the heliopause will be farther away and we run out of power before we get there, or if it will be closer and we cross it into interstellar space. That’s part of the excitement of that part of the mission that’ll come after the planetary science is more or less done, which will probably be in the 2020s. That will be a very valuable mission scientifically because the instrumentation on board New Horizons is a generation more sophisticated than the Voyagers carry. So, we can learn new things about that whole region of the Solar System with these much more sensitive instruments.
Jim Green: One of the things that New Horizons is doing between now and when it flies by MU69 is looking at other Kuiper Belt objects. What do you hope to achieve by doing that?
Alan Stern: We’re trying to put MU69 in context. We’re going to swoop down on it and study it with this spectacular battery of instruments and get all this detail, but the question is, how do the other ones look in comparison? What are their shapes like? How many satellites do they have? What are their surface properties like, compared to MU69? So, we’re actually looking at dozens of other [objects] with our telescope camera, called LORRI, on board, and not just before MU69. There are a lot of them to look at after MU69, because the Kuiper Belt doesn’t run out. It actually turns into what’s called the Extended Belt, or the Scattered Disk, that goes out hundreds of astronomical units. So, it’s all about context and making sure that we understand this valuable data set at MU69 compared to all the other things out there in the Kuiper Belt.
Jim Green: I always ask my guests about what their ‘gravity assist’ was. What really got you excited about what we’re doing today?
Alan Stern: Well, I’ve had a number of gravity assists in my life, but I want to tell you about a very special one that occurred just a few weeks after the New Horizons fly-by. I was in Vermont at a convention of amateur astronomers in August 2015, and after my talk was over and most of the crowd had dissipated, there was someone there who said, “I’ve just been waiting and waiting to come up and tell you something.” She said, “You know, people often say that our generation missed the boat on history, that we didn’t see the great world war that triumphed over evil, and we didn’t have a chance to see the Moon landings or the birth of the computer revolution that we all live with now, and so many other things. We often hear the meme that we came too late for all those historic things.” Then she said, “I just want to tell you New Horizons is the best thing that’s ever happened in my lifetime.” And, wow, what a gravity assist for a scientist to hear something like that, when you’re a physicist and a planetary scientist who works on the research aspects and the technical aspects, and to hear that you could change people’s lives with the project that we did and that those of us on New Horizons could actually inspire someone that way, that was my gravity assist. And, it’s going to power me for the next 30 years to do more exploration.