Artist illustration of New Horizons with Pluto and Charon. Image credit: NASA/JPL. Click to enlarge.
Listen to the interview: There Goes New Horizons (4.5 MB)
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Fraser: Congratulations on the launch of New Horizons. That’s got to be a big relief.
Alan Stern: Yeah, it’s wonderful to have a spacecraft on the way.
Fraser: So you’ve got 9 years ahead until you reach Pluto. Can you describe the path the spacecraft’s going to take, and what you might be seeing along the way?
Stern: Sure I can. First, it’s easy to remember, we’ve got 9 years on the way to the 9th planet. Our trajectory takes us first to Jupiter for a gravity assist. And we will have closest approach to Jupiter on the 28th of February next year, 2007. Following that, we have a long coast out to Pluto. About 8 years worth. And then we begin the encounter in the early months of 2015.
Fraser: Now as I understand, you’re going to just be going right past Pluto, get some photos on the way, but you’re definitely not going to be able to stick around.
Stern: Well, we have a long encounter. It’s about 150 days of observations of the system on the way in. And then we’ll make some observations on the way out as well. We have 7 scientific instruments, so it’ll be a pretty intensive course of observations. I think it would be selling it short if I characterized it as taking a few pictures of Pluto.
Fraser: And you’re going to be able to do a close flyby of its moon as well?
Stern: Well, you know Pluto has 3 moons. We’re flying through the Pluto system with very specific targeting because there are specific events that we want to make happen. Like we want to make the Sun rise and set so we can study Pluto’s atmosphere; and make the Earth rise and set for similar reasons – for both Pluto and Charon. And so, as we go through the system, all of our closest approach distances are set by those constraints. But we have very good telescopic cameras, and they’ll be studying Pluto, its 3 known moons, and any other moons that we find between now and 2015.
Fraser: And I think that one of the exciting parts for a lot of people is just to see it in photographs up close, because right now, all you get to see are some blurry pixels from Hubble. But just getting some pretty pictures isn’t everything. What’s some of the science that you’ll be pulling from this mission?
Stern: Well, quite a bit. First, this is the first exploration of a fully new type of object – these so-called ice dwarf planets. And so our objectives are very broad. To map Pluto and all the Pluto objects in the system. To map the surface composition as well, so that for every pixel we have a spectrum to determine what things are made of. And to assay the structure and the composition of Pluto’s atmosphere. Those are our 3 main objectives. We’ve got about a dozen others. But unlike a mission like Cassini or Mars Reconnaissance Orbiter, where we’re going back to a target we have visited in the past several times, this time it’s a real first time exploration, so our objectives more have to do with the data sets that we want to collect, and the specific answers we’re answering. We expect to be surprised when going to a new type of object; it’s always been the history in this type of planetary exploration.
Fraser: Well, I guess that’s the thing. Each mission tends to come up with some surprises. Obviously you don’t know what things are going to surprise you, but do you have some hunches on some stuff that you might be finding out?
Stern: We’re very interested to know the structure of Pluto’s atmosphere; what its dominant constituent is. We think we know from the ground, but we’re not sure. We have a hypothesis that Pluto’s surface will be young because the atmosphere is rapidly escaping. It’s removed the ancient terrains by escaping into space. There may be some evidence that Pluto is internally active, so we’ll be looking for evidence of that. For example, in the form of geysers or volcanoes; recent tectonic features, or flows. Similarly on Pluto’s largest moon, Charon, we’re going to be looking for ancient terrains; we’re going to be looking to count craters that tell us the history of the ancient Kuiper belt. And we’re going to be looking to see if we find ammonium hydrates, which have been detected at unfortunately tantalizingly low signal to noise by ground-based observers. But it would say a lot about small worlds.
Fraser: I heard recently that Pluto’s colder than people were expecting. That Charon is actually warmer. Will you be able to do some followup on this?
Stern: I’ll say a word or two about that, because I saw that reported in the press. It’s an incorrect story, in fact, exactly that result was obtained in the 1990s by two groups, published both in Science and the Astronomical Journal. So, I think the press release was flawed. Those results had been obtained about 12 years before.
Fraser: Not new… okay.
Stern: It’s correct, Pluto’s colder than Charon. It’s not colder than expected, because we’ve expected since the early 1990s. Pluto’s exactly the temperature that was found.
Fraser: Right, well I guess the hypothesis though, is that Charon is the result of a large object slamming into Pluto and turning it into a moon, sort of like our own Moon was created.
Stern: That’s right, but it has nothing to do with the surface temperature.
Fraser: Once the spacecraft gets past Pluto, and heads out, where do you want to go next?
Stern: Well, our secondary objective of the mission, and to a lot of scientists, it’s the primary objective of the mission is to see Kuiper Belt objects; the building blocks out of which Pluto and Charon were made. And so, our plan is to go onto one or two, or possibly even more Kuiper belt objects in the years following the Pluto encounter as we move further outward in the trans neptunian region.
Fraser: And I guess that’ll tell you how Pluto might be similar or different to those objects.
Stern: Right, exactly, we want to look and understand the composition of these bodies, learn their histories, and see whether they have atmospheres, the nature of small satellites around them. Count craters on their surfaces to compare to the bombardment of Pluto, and understand the accretion of these bodies.
Fraser: And if you had more time for a longer mission, or more advanced technology that you could put into the spacecraft, more powerful propulsion, what were some stuff you wished you could have added onto the mission if you had more budget?
Stern: I don’t really have any thoughts about the propulsion, and other fantasy land things. We built the mission when we could, and of course in the future decades or centuries, you could always do it, but it was time to do a Pluto mission. You have to build it with the best technology available. If spaceflight’s typically about the very real world engineering problems, were you have constraints of budget, time, mass you can send, things like that. But if we could suspend all belief, and remove those, it would have been very much to our liking to have flown a longer wave infrared spectrometer, so we could look for things like oxides of sulphur on the surface of Pluto and other bodies that we fly by. Perhaps a magnetometer as well.