Titans of Science: John Zarnecki
PodcastsThe Naked ScientistsTitans of Science: John ZarneckiPushing the boundaries of space exploration. . . 27 January 2026Titans of Science is back with John Zarnecki, a towering figure in the UK's space. . .
PodcastsThe Naked ScientistsTitans of Science: John ZarneckiPushing the boundaries of space exploration. . . 27 January 2026Titans of Science is back with John Zarnecki, a towering figure in the UK's space community. He has played a crucial role in designing instruments for groundbreaking space missions, and has also helped shape Europe's planetary science programme. In this episode, John shares compelling stories from his career with Chris Smith - including the significance of the Cassini-Huygens mission to Titan, the value of the Hubble Space Telescope, andhis early work on rockets in Australia. . . John Zarnecki: rockets, comets, and telescopesJohn Zarnecki, The Open UniversityJohn Zarnecki was born in London on the 6th November, 1949. He attended Highgate School in north London where, in 1961, pupils were given the day off to see the first man in space, Yuri Gagarin, visit the tomb of Karl Marx at nearby Highgate Cemetery. John was among them. From an early age, perhaps motivated by seeing Gagarin, John developed a fascination with space. He went on to study Natural Sciences at the University of Cambridge before graduating with a doctorate in Physics and Astronomy at University College London. John later made significant contributions to the field of astronomy. Alongside his team, he helped develop scientific instruments for a range of space probes and telescopes. These included the Hubble Space Telescope, the Giotto probe which studied Halley’s Comet, and the Huygens probe that landed on Saturn’s moon Titan - making him a truly genuine Titan of Science. This work earned John and his colleagues the International Academy of Astronautics’ 2006 Laurels for Team Achievement, and the NASA Group Achievement Award. John also served as the Director of the International Space Science Institute, and is currently an Emeritus Professor of Space Science at the Open University in Milton Keynes. Chris Smith began by asking him when he first realised he was destined for a career in space science…John - I saw an advert, I don't know where it was, maybe New Scientist, something like that, from UCL and basically said, come and do a PhD with us and you can launch rockets in Australia. I couldn't resist that, it was just a fabulous opportunity, you know, to go and launch rockets because I was a product of the 60s, you know, I'd grown up with the space age, I'd loved the theatre, the drama of the space age, which I'd watched on our grainy black and white television at home. So the opportunity to work on instruments that would go on Skylark sounding rockets that are launched from the Woomera rocket range in South Australia and they give you about 10 minutes above the Earth's atmosphere and the thrust of the UCL group was X-ray astronomy. So it was a very young branch of astronomy and X-rays of course are absorbed by the Earth's atmosphere, which is a bad thing from the point of view of astronomy, but for us as humans it's rather good because X-rays are very dangerous, it's partly why there's life on Earth. But then with the advent of the space age we could build X-ray telescopes if you like, put them on these rockets and start to explore this new aspect of the electromagnetic spectrum because for millennia we had been only able to use visible light. Then of course since the 40s, 50s we'd been able to do radio astronomy and then this was another part of the spectrum, the electromagnetic spectrum, that was opened up by the advent of space vehicles. Chris - Was the recording made while the rocket was airborne then? Was that why you said you get 10 minutes, you get it up there and you've got enough time to make some observations? How do you get the data back?John - Okay, there's a telemetry system on these rockets, generally, so the data is relayed in real time down to the ground. I started with my own project, I mean this was unbelievable, I was I think 23 when I was given a Skylark rocket of my own. Chris - They sent you to Australia to launch rockets?John - Oh absolutely, absolutely. My PhD project was Skylark 1012, 1-0-1-2, and I mean it was just a wonderful experience, it was sink or swim. This was the Mallard Space Science Lab, which is part of University College London, which had tremendous expertise, you know, in electronics, in mechanical engineering and there was no formal training you learnt on the job. Chris - Quite amazing, I can't see that happening today, can you?John - No, absolutely impossible, but I mean what a way to learn and these, I mean they were risky projects and of course sometimes they failed. Chris - You got a PhD though, so you didn't fail, so you must have got data?John - Oh absolutely, we were looking at a supernova remnant, so a supernova remnant is what is left over after a star goes bang. Most people have heard of supernovae, they're these very dramatic events, but what happens afterwards? You get an enormous shockwave ploughing out into the interstellar medium, very hot material, which is, because of the temperature, it's emitting mostly in X-rays and so the one that I was looking at, Puppis A supernova remnant, in the southern sky, in one of the brightest X-ray sources, about 40,000 years old and we were not sure why supernovae, or remnants of them - and there were several that had been detected - why, you know, what was the mechanism that was producing the X-rays and there were two possibilities. And so if we could see a spectral line in the emission of X-rays, that would tell us that the mechanism was what's called Bremsstrahlung radiation, that's thermal radiation, basically, the X-rays are being produced because of the heat. The X-ray detectors then had very, very poor spectral resolution, it's very difficult to pick out colours if you like, X-ray colours, so we built a Bragg crystal spectrometer, that's a device which basically enabled you to look at X-ray colours and we detected, for the first time ever, an X-ray spectral line from an X-ray source other than the sun. Chris - We take all this for granted these days, don't we? I mean, you must look back on that and think the effort you had to go to, to make that measurement, and now you've got people building telescopes where they're surveying half the universe in an evening, I mean, it's eye-watering now, isn't it?John - Absolutely right, and this was because in the early days of space-based astronomy there were very few, if any, satellites available for that, so, you know, the early days were done with sounding rockets, you had at most 10 minutes of observation, so by the time the rocket had locked onto the object, you know, was pointing in the right direction and that was very difficult to achieve, we only had two minutes worth of data and I got this little hump, you know, in the spectrum and it was just enough to be able to stick your neck out, publish a paper and say we've detected an X-ray spectral line. Go on about eight years, and one of the first satellites that was devoted to X-ray astronomy was able to look at this object for 10 hours, and the little bump that I detected was resolved into three separate spectral lines. You know, it could just stare for 10 hours instead of my puny two minutes, and of course, you get so much more light, so much more x-rays, you can really, you know, see what you're doing then. Chris - But it was there, that's the critical thing, and you were proven right, but how did you end up then, because really the defining thing in your career must be to say you have put a probe on the biggest moon of Saturn? So talk us through that journey - I don't mean as in launching the probe yet, but how did your career begin to evolve that would take you in that direction?John - I loved pretty much everything about it, the discipline of being a rocket scientist, but also the technology that went into it. When I finished my PhD and had to, you know, look at where to go and what to do, it was actually a recession of the late 70s, jobs were incredibly difficult to come by in the universities, so in fact I went into the aerospace industry, to British Aerospace, who had what looked like a very interesting project, it was called at the time the Large Space Telescope. Now you probably know it differently. While I was working on it, it was renamed the Hubble Space Telescope. Now, a lot of people don't know that, actually, about 20 percent of Hubble, even to this day, is European. So of the original five instruments, one was European, that was the faint object camera, and that was designed and built in Germany and the UK. So I went to British Aerospace in Bristol to join the team working on building the faint object camera. Chris - It wasn't your mess up that meant the mirror was wonky, was it?John - No, that was the Americans, I mean, what do they know? It was a company who, in fact, changed their name not long after that disaster, so that they wouldn't be associated forever with that. Chris - It did get fixed, though, didn't it? Because that was another amazing space first, that not only had we put this thing in space, but realised what the problem was, and then were able to deploy a mission that fixed it in situ. I mean, obviously, it's a bolt-on to fix it, but then look at the outcome, look at the results. John - Absolutely, and of course, Hubble was pretty much the first space instrument, at least of any size, that was designed from the very beginning to be serviceable by astronauts, delivered by the space shuttle. So, you know, without that, it would have been just a disaster. It would have, you know, never worked properly. Chris - Your engineering stood the test of time there, hasn't it? Because you think decades later it's still up there, it's still working, we're still doing science with it, in a really very inhospitable environment. John - Absolutely. Even when we were working on it, it was fairly old technology. The core of the detector and camera system was what's called a vidicon, which, you know, goes back to the 30s, the technology. I mean, it was a very sophisticated vidicon, but it was already kind of old-fashioned when we launched in, what? 1990, I think it was. That instrument lasted for 12 years and was replaced. All of the original instruments have been replaced, and much of the electronics. But yes, it's a remarkable testament to good design. Chris - Did your time with British Aerospace end then with the launch of the Hubble? Was that the project, or did you carry on for a bit longer? How did you then get back into, shall we call it, proper science, where you're actually leading research?John - Yeah, well, I spent three years at British Aerospace, and it was a tremendous experience. I learnt a lot about the, if you like, the formality of how you build instruments, and the rigour, quality assurance, and so on, which, you know, is kind of difficult to learn about in the universities, and is more important probably on long-term satellite missions than a short-term rocket flight. In the end, I was slightly frustrated. I missed the what, the cut and thrust of the academic world, and, you know, you're more able to try new ideas and new things. And I saw an advert for a job to work on a mission to go to Halley's Comet. It was like, you know, seeing the advert to go to Australia and launch rockets in the desert. It was just too much to resist. So this was the Giotto mission of the European Space Agency, and I would say this was the first really, really daring project that ESA had undertaken. Chris - What was it going to do?John - It was going to go to Halley's Comet, fly past it at a close, close distance, and for the first time see what is really at the core of a comet, because we, you know, with the best telescopes on the ground, you just cannot see what is at the heart of a comet. You see a head, a coma, and a long tail stretching out, but you just don't have the resolution to know what is it that's causing this phenomenon. Chris - 1986, was it, Halley's Comet came on its closest flyby?John - So I moved to the University of Kent, where Tony McDonnell, who's my boss there. He had been selected to provide one of the, I think, 12 instruments for Giotto, an instrument to measure the dust particles, which make up much of the comet. And I moved there in 1981, not long after the mission was selected. Chris - So there's a five-year lead time to do this?John - Well, in fact, the launch was ‘85. It was something like a nine-month journey to meet Halley's Comet. So the launch was mid-85, arrival was March ‘86. And the thing about Halley, it's, I mean, it's been observed for centuries, and we know its orbit very well. It is one of the most active comets, so that means there'd be a lot going on to measure and observe. But its orbit is retrograde, which means it's going around the Sun in the opposite direction to the Earth and the planets. So it inevitably means that the relative speed between your spacecraft and the comet is going to be very high. In the case of Giotto and Halley, it was 68 kilometres per second. Goodness knows how many tens of thousands of miles an hour. So the decision was taken from the start that this would be a kamikaze mission. We would go as close as we could and with the expectation that the spacecraft would be destroyed, because at that speed, even a tiny dust particle, you know, milligrammes would be sufficient to do irreparable damage. Chris - We were talking about space debris on the programme recently, and one of the Warwick scientists who works on this said a centimetre cubed particle in space at the trajectory and rate they're moving has the energy of a hand grenade. I mean, so something like what you're saying would just destroy your spacecraft very, very quickly. John - Absolutely. And I mean, in low Earth orbit, debris typically has speeds of seven kilometres a second. We're talking 68 kilometres a second. So in fact, Giotto was designed with a dust shield. This was sometimes called a Whipple dust shield, proposed by, in fact, a cometary scientist American by the name of Fred Whipple. He wrote this up in the 1950s before even Sputnik 1. And so this was basically two shields at the front of the spacecraft. The first shield would break up a particle and then the second shield about 20, 25 centimetres behind would then absorb the shock that had been generated by the impact on the front shield. We were hoping that that would enable us to get close, but we knew we would almost certainly be destroyed. Chris - Did it work?John - Yes. In fact, it worked better than we'd expected. So the decision was taken just a few days before encounter - we would aim for a missed distance of 600 kilometres. One of the most bizarre meetings I've been to was when PIs, the principal investigators, the head of each instrument team, was arguing for what distance to go for. Some wanted to go for zero to actually try and smash into the comet. Others wanted to go further away, which would give us a chance to survive and make more distance measurements. So 600 was the compromise. And actually, what was achieved was 594, so staggeringly good. And I'll never forget that day. We're watching the data coming in and, you know, we're being bombarded with dust particles which are hitting the spacecraft. And at about a missed distance of 2,000 kilometres or so, the screens went blank. We'd lost it. We'd assumed that the spacecraft was destroyed. And, you know, the champagne came out. We were all absolutely ecstatic. After about, I can't remember, 20 or 30 minutes, somebody shouted out, hey, there's some data on the screen. Communication had been re-established. But what had happened was that a big particle, and big is a few milligrams, I kid you not, had knocked the spacecraft. So it had started wobbling. So the data beam back to the Earth was missing the Earth. But there was actually an on-board damping system. So after this 20 or 30 minutes, the link was re-established. And we were getting data as the spacecraft was going away out from Halley's Comet, which was absolutely remarkable. Now, when we, you know, finally analysed all the data, we realised that several instruments had been damaged. The camera was destroyed. We had six or seven dust instruments and two of them were destroyed. But basically, the spacecraft was functioning. It had lost some bits and pieces, and to cut a long story short, the spacecraft was put into hibernation - I think the first time that had ever been done in deep space - and it was re-targeted to encounter a second comet. We flew past the Earth in 1990, which gave us a kick and modified the orbit because there was no onboard fuel to do that, and in 1992, we encountered a second comet. And I mean, it's absolutely remarkable, and I think it was so important for the European Space Agency. I think it gave them the confidence that they could do difficult, exciting stuff, and I think the rest of the space world said, hey, this is a serious organisation. John Zarnecki: Titan, Saturn, and beyondJohn Zarnecki, The Open UniversityChris Smith first crossed paths with John Zarnecki in Cambridge during the 1990s, when Chris was immersed in his medical studies. It was there that John revealed his plan to land a probe on Titan - which is Saturn's enigmatic and clossal moon. . . John - There were six instruments, six scientific instruments on the Huygens probe, and I was one of the PIs, one of the six leaders. And of course, with all of these projects, there's an enormous team involved. I mean, not full-time, you know, some come and go, teams in space agencies, in industry. In fact, one of the things that I loved about the work was this collaborative way of working and, you know, I mean, being a child of the 60s, a bit of a hippie, really, you know, this is an example of people working together for no reason other than pure science. Chris - Why did you pick Titan?John - It picked me, really. Science missions are selected competitively. It's really very democratic. And so after Giotto, I got involved with doing studies for a mission called Vesta. This was a French-Soviet ESA mission to go to an asteroid and to fire a dart, if you like, a penetrator into the asteroid to try and make measurements, and this was in competition. I think there were five or six missions in the competition. And I remember going to Bruges in Belgium, where there were the presentations of each of the missions, and then the top committee in ESA would go away, deliberate and decide which one to choose. And to my horror, rather than choosing Vesta, which was clearly a magnificent project, they chose something which I think at the time was called the Titan probe. It was a project to work with NASA. NASA would provide a big spacecraft called Cassini, and Europe would provide a probe, a smaller probe, that would be detached and would land on Titan, the largest moon of Saturn. Chris - Did you know much about Titan at the time? Or do you just sort of have this as an afterthought, “Oh, it's a moon I've heard of”?John - It was a moon I've heard of. I hadn't published a single paper with the word Titan in it, but I remember going back to our lab, really deflated and saying to my colleagues, you know, we spent a year working on this Vesta project, we've done some interesting work, is it all wasted? Can we adapt any of it and use it for this dreadful mission, which ESA and NASA have chosen, which, you know, maybe we can get in on it? And so we sat down, and I literally remember it was a coffee break, and we had a new coffee room, and we went in there, and we got an enormous sheet of blank paper, and I said, “Right, if you land on a somewhat mysterious and unknown moon on the surface, what measurements would you like to make? And is there anything that we've done that could contribute to that?” So we wrote down just all of the physical and chemical properties that we could think of. Remember, we knew virtually nothing about the surface of Titan. Chris - It's shrouded in a very dense atmosphere and bloody cold. It's what, minus 200 degrees or something, isn't it?John - Minus 180, yeah, something like that. And it's covered, Titan, which is the second-largest moon in the solar system, but it's shrouded in orange smog. So the Voyager 1 spacecraft had flown past in the early 1980s and produced a couple of thousand of images, all of which showed basically an opaque orange blob, no view of the surface. Chris - Was that the attraction then? Because it was mysterious, people thought, let's go there. John - More than that, there was lots of data about the atmosphere from the Voyager flyby, and the inference from that was that the surface could actually be covered with liquid. Not water, of course, at minus 180, but hydrocarbon, so liquid methane or liquid ethane. So there was a real possibility that this was a really exotic place, the only other place in the solar system with liquids on the surface, and the fact it is also the only moon in the solar system with an atmosphere, a thick atmosphere. So really it stands out for all sorts of reasons, and that is why the target of the Cassini-Huygens mission, as it came to be called, was the Saturnian system, but with an emphasis on Titan. Chris - And how did you get in on the action then? Was your pitch that, well, we actually know how to do some of this stuff then, and this is what we think we can deliver?John - Yeah, sort of. Basically, ESA threw open - this is normally the way it works - the opportunity to propose an instrument. So they would say, we have committed to fly this mission, it's got this much mass, volume, power, data available; we think we should fly these instruments, so respond to this AO, we call it, announcement of opportunity. So from that started over coffee, I put together a team - international team - and we proposed a collection of instruments called the Surface Science Package. Basically nine individual sensors, which would, each of which would try and make a particular measurement on the surface of Titan, and this was particularly difficult because, A, we didn't know if the surface was, could have been hard ice, it could have been a gooey, tarry surface, it could have been liquid methane lake or sea. And also we had no idea how long we'd survive. ESA always told us we should aim for three minutes on the surface, so most of the measurements of the six instruments would be done during the descent and maybe we'd get three minutes on the surface. So we made a proposal to fly this instrument and we were selected. Chris - That took off in 1997. It reached the Saturnian system in 2004. What was then the process to get to Titan? Because that was just Cassini-Huygens got there. How did you then get to Titan?John - Once Cassini-Huygens had been captured into orbit around Saturn, Huygens was released just on a set of springs. It was essentially pushed away and it was then on a ballistic trajectory, so it had no rocket power, it was just on a path, on an orbit that would take it inexorably three weeks later to Titan. It would hit the atmosphere, had a series of three parachutes, so it would sail down to the surface in two and a half hours, something like that, land on the surface, and if we were lucky, it would survive for, well, we were designing for three minutes. As it turned out, we got 72 minutes on the surface. Chris - Was your heart in your mouth? Because you must have been, because you went to America to be at mission control for this coming down the descent, didn't you?John - The descent was monitored and controlled from ESOC, we call it, European Space Operations Centre in Darmstadt in Germany. I mean, it was the highlight, I suppose, of my professional career. This was the culmination of 15 years of work. And I mean, you do have to be a little bit mad to do this sort of work because it could have been lost just like that. We could have ended up with zilch, no data whatsoever. And I mean, there are many bizarre aspects of it. One is that we were monitoring essentially what had happened four or five hours previously, because the data could not be transmitted straight to the Earth. It was transmitted from Huygens, our probe, up to the Cassini spacecraft, which was flying over Titan, you know, a few thousand kilometres away. Cassini would record the data, and then it would turn to point its large antenna to the Earth, and then it would squirt the data down to Earth. And so this all meant that we got the data four or five hours after whatever had happened had actually happened. So that was kind of bizarre. Chris - I bet you were standing there watching the clock, thinking, “It's now in the lap of the gods. This thing has, whatever's going to happen has happened. Now I'm waiting for the radio signals to make it all the way back across the solar system. ”John - I mean, it was a highly emotional culmination of all these years of work. And we'd worked as a team pretty much very closely together. Chris - What did you learn about Titan, though? What did that magic 72 minutes, that you were hoping for three and got 72, what did it reveal?John - Well, that Titan is really a remarkable place. The surface is mostly icy, but about 10% of it is covered with lakes and seas of liquid ethane, mostly. The largest sea is larger than the largest of the Great Lakes, for example. And the atmosphere is thick; we know a lot about its composition, and we know a bit about what’s underneath the surface, the icy surface, and there’s a real possibility that there is a sea, a sub-surface sea. So it’s a truly remarkable place, Cassini-Huygens just scratched the surface, and this is why now NASA are building a mission to go back to Titan due to launch in, I think, in a couple of years.