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August 21, 2005
Professor John C. Zarnecki, Principal Investigator, Huygens Surface Science Package, 7/27/05
Dr. David Lemberg: Our next guest is Professor John Zarnecki, Principal Investigator for the Huygens Science Surface Package, and Professor of Space Science, Planetary and Space Sciences Research Institute at the Open University, located in Milton Keynes, United Kingdom. Since 1990, Professor Zarnecki has been Principal Investigator on the Huygens Mission, part of the ESA/NASA Mission to the Saturnian system, and Saturn’s largest moon, Titan. On January 14th, 2005, Huygens touched down on the surface of Titan, by far the most distant landing ever achieved.
Professor Zarnecki’s Surface Science Package produced over 3.5 hours of data in Titan’s atmosphere and surface—the data are currently under analysis. Professor Zarnecki is involved in a variety of national and international advisory bodies in the field of space research, and he’s also active in the field of public understanding of science. Welcome, Professor John Zarnecki.
Professor John Zarnecki: Hello there, David.
Lemberg: John, thank you. I know it’s the evening in the U.K., thanks for taking the time to be with us.
Zarnecki: It is, indeed, in fact, though it’s mid-summer here, it’s a gray, damp evening, so it’s good to talk to you. I assume the sun is shining where you are.
Lemberg: It is! John, first, congratulations on the spectacular success of Cassini-Huygens. This is just wonderful for all of us.
Zarnecki: It is, absolutely, and I must say, though, it’s several months since we landed on Titan. I must say that my feet have barely touched the ground since then. I think I’m just about coming down to reality, but yes, it was a day, January the 14th, that, of course, I will never forget.
Lemberg: Yes, and it’s just so great for all of us. I mean, of course, this was science fiction years ago. Can we start by talking about why a mission should go to Titan?
Zarnecki: OK, at one level, that’s very simple. I mean, we’ve got a lot of satellites of the planets in our solar system. In fact, we know of well over 100 satellites, either quite large objects, down to very small objects, the smallest that we know, literally, only a few miles across. But, Titan absolutely stands out, and it’s not just because it’s a relatively large satellite. It’s not the largest, it’s the second largest. Ganymede, which is a satellite of Jupiter, is just a bit larger. Titan is larger than Mercury, for example, so it sort of stands as a small planet, in its own right, just on the basis of size. But, there’s one thing that absolutely makes it stand out, and that is the fact that it has an atmosphere, and that is pretty much unique amongst all of the satellites. And, it’s a really thick and complex atmosphere, so it really does stand out, on that basis, alone.
Lemberg: So, it’s a nitrogen, and complex hydrocarbon atmosphere?
Zarnecki: That’s right, so the main constituent is nitrogen, as you say, like our own earth. But, from then on, it deviates from our own atmosphere. And, it’s the hydrocarbons, or the gases consisting of carbon and hydrogen which make it particularly interesting. These are quite reactive gases, and when you shine sunlight on them . . . now, I know that Saturn and Titan are a long way away, so the amount of sunlight they get is only about 1% of the amount of sunlight that we get. Saturn is 10 times further away, and if you square 10, you get 100, so it’s 100th of the sunlight. But, still, that sunlight, and particularly, the ultraviolet light initiates chemical reactions in the atmosphere, in the hydrocarbons.
And, it is believed that, you know, there’s a whole chain of chemistry taking place in the atmosphere, and that is one of the reasons why we’re particularly interested in Titan.
Lemberg: Well, nitrogen, and complex hydrocarbons, if there was oxygen, then you might have proteins.
Zarnecki: That’s right, but one vital fact that you should know is the temperature. And, this is simply a function of how far away Titan is, and because of the very low sunlight. And, it means that it is very cold. In fact, we knew, even before Cassini-Huygens arrived, we knew this from the Voyager Flyby in 1981, the temperature on the surface, and in the atmosphere, is around minus 180° centigrade. So, this means that the oxygen, which is predominantly in water, is locked up as water ice. So, Titan is, basically, a big ball of ice, and there is very, very little free oxygen at all, almost no free oxygen in the atmosphere. It’s tied up in the water ice in the solid surface.
Sam Kephart: John, one of the questions I have is this whole issue about . . . and, I know there’s a lot of scientific argument about it, but you’re on a satellite that has an atmosphere—this whole question of, are there other planets or satellites that had atmospheres and lost them, and if so, why?
Zarnecki: Well, I mean, this is the unknown, and this is one of the questions I hope that we will answer when we’ve analyzed all the data. And, I should say, and this might sound like an excuse, but bear with us, because it’s a really tough job analyzing this data. It was only January when Huygens arrived and descended. I should say that Cassini, the mother craft, which carried Huygens, is continuing to orbit around the Saturnian system, and every 40 days or so, we get a flyby of Titan.
So, in fact, I think the strength of this project, or one of the many strengths, is that we’ve got the combination of 3.5 hours worth of in situ data, so that’s data from Huygens, in place as it descended through the atmosphere, and landed on the surface. And then, you couple that with data from about 40 different flybys from Cassini. Now, these will be from the whole battery of instruments on Cassini. There’s a fabulous radar. There are various in imaging instruments. There’s spectroscopic instruments, taking measurements on each of the flyby of different parts of Titan.
Remember, when we landed on Titan, we, of course, just sampled one region. So, the real strength is going to come when we’ve put all of this massive data together, and we’re talking about really, several years to process all this, to understand it, and, hopefully, to change our theories and our understanding of Titan. And, not just Titan, of, perhaps, any place like the earth, and, hopefully, some of the extra solar planets, where organic chemistry has started, and primitive, or not so primitive life might have developed.
Lemberg: John, thank you. We’re sitting here with big smiles on our faces. It’s just so great. I know you’re the Principal Investigator for the Huygens Surface Science Package. Can you tell us about that particular mission?
Zarnecki: Indeed. This was one of the six instruments on board Huygens. I should say, if you allow me to digress just for a minute . . .
Lemberg: Sure.
Zarnecki: One of the great things about working on this project was that it was just a fantastic collaboration between NASA (that you’ll be very familiar with, of course) and ESA, the European Space Agency, which is our equivalent on this side of the Atlantic, must smaller than NASA, but still we’re an active player in space. And so, the instruments on both Cassini and Huygens were a real mixture of scientists and engineers from Europe and the U.S. So, I led the team that provided the Surface Science Package.
Now, what you should appreciate, is that we actually, before Huygens, we never saw the surface of Titan. Titan’s atmosphere possesses a haze, a very thick haze or a smog, which meant that we could never see the surface of Titan. Now, there were indirect measurements, and some of these suggested that the surface, or at least parts of it, might be covered in liquid hydrocarbon, so that’s things like liquid methane, liquid ethane, the sort of thing that, certainly, in my country, in England, we call LPG, liquefied petroleum gas, and some people run their cars, use this as a fuel.
So, we didn’t know if we were going to land on a solid, on an icy surface, or we were going to land in a lake, or even a small sea of liquid methane. Methane is liquid at the surface conditions on Titan. So, my instrument, Surface Science Package, designed to try and measure some of the physical properties of the surface, had a real dilemma. How on earth do you design instruments for you don’t even know what you’re going to land on? So, we came up with a collection of sensors, quite simple sensors, they’re quite clever, some of them, nine different sensors which, between them, we believed would cover pretty much any landing scenario, a hard landing, a liquid landing.
Some people have even suggested that the surface might be covered with a hydrocarbon, I like to call it a goo or a gum, something like tar, you know, the sort of thing that if you ever see pictures of when an oil tanker breaks up and deposits dreadful deposits on the sea coast . . .
Kephart: Like a sludge.
Zarnecki: A sludge, that’s a lovely word. So, it could have been that. So, we came up with a collection of instruments to try and handle any of these scenarios, which meant that whatever we landed in, some of the instruments probably would work, and some wouldn’t. Well, to cut a long story short, we didn’t splash down in a liquid. We landed in what looks like a dried up lake bed. It’s very clear from the images. I’m sure you and many people will have seen some of the images. We see what look like river beds, lake shores, but we don’t actually see yet, although, perhaps just recently, that has changed. But, certainly, if you’d asked me the question two weeks ago, I’d have said, “There’s no compelling evidence for standing bodies of liquid, but clear evidence that liquid has flowed, in the past.”
Now, with one of my instruments, it’s actually called a penetrometer, so this is, essentially, a stick which protruded through the front of the probe, and it drove into the surface before the large Huygens probe behind it, smashed into the surface. We measured the physical properties of that surface, and what we think it is, is Titan’s equivalent of sand. Now, on the earth, of course, sand on the seashore and on a river bed is made of rocky material, it’s a product of water flowing over rocks.
On Titan, we have a liquid, but it’s not water, it’s liquid methane, and the bed rock is not rocky stuff, it’s icy stuff. So, it’s a sand made of, we think, tiny ice grains. And so, it’s wonderful. What we think we’re seeing on Titan are physical processes we see on earth, but using alien materials instead of, as I said, water and rock, because the earth is, basically, a rocky body. On Titan, we see liquid methane and ice.
And, it’s fascinating. It’s early days yet, and we’re really only scratching the surface, and the people who have the chemistry experiments, those are really difficult to analyze. But, the first results are just beginning to come out.
And, in fact, we have, probably in about six week’s time, an issue of the journal Nature, which is one of the world’s leading scientific journals, and that’s going to have the first results from each of the six instruments on the Huygens probe.
Kephart: A very quick question, did the Huygens surface lander give up its life when it landed? I mean, obviously, you got several hours of data. Or, can you reawaken it from a deep sleep, given the very cold conditions there?
Zarnecki: Well, that’s an excellent question, and I would say, if only, no. We didn’t know how the probe’s life was going to end. It was either going to break to pieces on impact, it was going to run out of electrical power, because we’re running entirely on batteries. Or, it was just going to freeze to death, remember the temperatures?
So. . . and, in fact, also, the data, we couldn’t send it directly. It had to go via Cassini, which was flying overhead to act as a data relay. It lasted for 70 minutes on the surface before the link to Cassini was lost. Cassini, essentially, disappeared over the horizon, not to reappear for another 40 days, by which time, the batteries were flat, the beloved Huygens probe had probably dropped to –170°.
So, it really was a one off, it was a seven-year journey for, literally, 2.5 hours data during descent, and 70 minutes of data on the surface. But, still, I mean, that’s wonderful data, and until we go back, which I suspect will be, sadly, not for another 20 or 25 years, we’re all going to be pouring over every single bit of that data.
Lemberg: John, thank you for a brilliant conversation.
Kephart: Yes, we certainly hope you’ll come back soon. This is very important stuff.
Zarnecki: Well, it’s very kind of you.
Lemberg: It was wonderful, John, thank you!
Zarnecki: My pleasure!
Posted by David Lemberg at 02:11 PM | Comments (0)