Dr Hal Weaver, Johns Hopkins University
Part of the show Science Question and Answer - New Horizons Mission
Chris - We're going to be joined this evening by Hal Weaver who's from the New Horizons mission, and he's joining us now from Johns Hopkins University over in the States. Why are you going to Pluto? What's the point of this?
Hal - It's been dramatic how our image of the solar system has changed over the last ten years. Pluto's been at the forefront of that new understanding. There's been a big controversy about whether or not Pluto is a planet, but it's definitely something called a Kuiper Belt object. This is a new region just outside Neptune's orbit and it was just discovered in 1992. We now know of roughly 1000 objects out there and it's a whole new region of the solar system that hasn't been explored yet; a region that we're calling the realm of the icy dwarfs. Pluto is the prototype of those objects.
Chris - So what do we think is out there, Hal? What are these objects like and why are they worth studying?
Hal - They're worth studying for a number of reasons. One is that because they are so far away from the sun and outside of Neptune's orbit most of the time, they've always been cold since the time that they formed roughly 4.6 billion years ago. As you know, one of the best ways to conserve material is to keep it in a deep freeze. That's exactly what's been done with these objects. They've got a lot of ice and the molecules that they have retained over these last 4.6 billion years basically give us a window back to the time of the formation of the solar system. So by studying these objects now we have a much better insight into what's happening in the early solar system in that region of the solar system. This is in comparison to observing the Earth or other planets, where these objects have had so much evolution over the age of the solar system.
Chris - How long is it going to take New Horizons to reach Pluto? It left in what, February of this year wasn't it?
Hal - It was January the 19th of this year that we took off. We went screaming off the surface of the Earth; it was the fastest spacecraft ever launched going at about 36 000 miles per hour. But even going at those kinds of speeds it's going to take nine and a half years to get to Pluto because Pluto is so far away. It's roughly 30 times further from the Sun than the Earth is. So even though we had the most powerful rockets available and had a very favourable launch, it's going to take a long time. We're heading first of all towards Jupiter and one of the big reasons for going by Jupiter is to get gravity assistance. We're going to get a sling shot effect because Jupiter is so massive, and is by far the largest planet in the solar system with a mass of 320 times that of the Earth. The most important objective of our Jupiter encounter is to hit a little key hole in space; a little spot near Jupiter that will propel us on towards Pluto and cut off three to five years of our travel time and increases our speed by about 20%. But still, it's going to take about nine and a half years to get to Pluto. We know now that we're going to arrive on July 14th 2014.
Chris - How do you actually know that the probe is a) going to survive the journey, and b) be able to operate under those extremes of temperature? It must be about minus 200 degrees Celsius out there near Pluto. How's it going to operate?
Hal - Yeah that's right. There are very harsh conditions out there. But our spacecraft are actually nice and toasty; it's almost like a thermos flask. We have multilayer insulation wrapped around the entire spacecraft and just from the heat generated by the electronics, we generate enough heat to keep all the instruments, the spacecraft body and the telescope and so forth at roughly room temperature even when they're out by Pluto.
Chris - So what sort of science will you be doing at Pluto? In what way will you be interrogating that part of the solar system with the probe?
Hal - There are basically some questions that we want to address that are just too hard to do remotely. We are so far away from Pluto, so first of all we want to know: what does it look like in detail? The Hubble space telescope is the most fantastic space observatory available to us here on Earth, but it can barely resolve Pluto. It's done some magnificent imaging of Pluto but even with Hubble, it looks like a bunch of about ten pixels across. All you can tell is that there are some very bright regions and some very dark regions but it's very hard to tell what's going on. Why are these regions bright and why are they dark? We'll do thousands of times better than that by flying the spacecraft by.
Chris - And when you're out there, how long will it take a message or any of this data you're collecting to get back to Earth each time?
Hal - It's amazing. It turns out that from Pluto it takes four and a half hours for the light to reach the Earth. So the round trip will take about nine hours.
Chris - So it's a long old time. Once you've got to Pluto, will you carry on a go beyond the orbit of Pluto and keep exploring?
Hal - That's exactly right. What we're hoping to do is not to stop at Pluto but continue plunging into this region called the Kuiper Belt. As long as everything is still working then, we have a very good chance, we estimate something like 95% probability, that we'll be able to encounter another small Kuiper Belt object. Even with Pluto, we just discovered a year and a half ago two more satellites that Pluto has besides Charon, the one that was discovered in 1978. We have two more mini satellites; our own mini solar system out at Pluto, so effectively we have four Kuiper Belt objects to look at for the price of one by going past Pluto. The neat thing is that we have one of the largest members of that class and the smallest satellites in that system, and plus we hope to encounter more of the small Kuiper Belt objects to see whether they are like the objects of the Pluto system or very different.