What is Cassini’s main achievement?
Cassini has been a discovery mission. The only way you can understand a system is to orbit. The Pioneer and Voyager spacecraft gave us little nuggets on fly-bys in 1979 and 1980, but Cassini has given us the full picture. And it will allow us to decide what to focus the next Saturn mission on. Is it going to be Enceladus? Is it going to be Titan? Is it going to be a polar orbiter?
What is your own highlight of the mission?
Our instrument discovering an atmosphere on the moon Enceladus. But Titan has been absolutely spectacular, too. When we first arrived at Titan, we expected to see liquid on the surface, but there wasn’t any. It was maybe six years into the mission when the infrared spectrometer first saw the sun glinting off something at the north pole. That was the first view that we had of any liquid. The reason we hadn’t seen it before was because of the seasons. It just hadn’t rained.
Some of the discoveries at the rings, like the little moonlets that orbit around Saturn and change their shape, are breathtaking. And the images of the moons are just amazing. I think it just got more and more interesting as the mission progressed, and these days I get excited at almost any data set that comes in!
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Cassini’s grand finale:
Join us as we count down to the fiery end of the Cassini spacecraft’s mission to Saturn
Why has the mission been such a success?
The real strength of a large mission like Cassini is that it covers a whole range of different kinds of science, and gets the big-picture view. For me, the most fantastic thing is how this disparate bunch of scientists and engineers from around the world is working together as a team.
That’s partly down to meticulous planning. After lift-off in 1997, we had six-and-a-half years to decide what we wanted to do at Saturn. We would spend hours in teleconferences talking about the timing of every observation. To begin with, everyone wanted to do their thing all the time. But slowly, we got to understand each other’s science, and the team would say, you can you have that part of the orbit if I can have another. That time was really good for us, because it got us working together as a team.
Were there moments when you worried Cassini wouldn’t achieve all that you had planned?
Plenty. At launch I was absolutely terrified. I had just taken over the leadership of the Cassini magnetometer. I gave the impression I knew what I was doing, but I didn’t. We got up three mornings in a row at some ungodly hour because the launch was going to happen at two in the morning. Two days in a row, it was postponed because of upper winds and things like that. When it finally happened and you’re watching this thing go up, the ground shakes and you’re standing there, thinking, “I hope it’s going to be okay. I hope it’s going to be…” And your heart is in your mouth. It really is.
And then when we first got to Saturn, we were due to come up through the gap in the rings – which you hope lives up to its name, the “big empty” – and you’re biting your nails and not sleeping for days in case you hit something that wipes out the instrument you’ve built. And now, with the end of mission stuff, the spacecraft is doing things it was never designed to do and we’ve all had our hearts in our mouths again. So there’s terror and fear and great excitement and then more terror and fear.
And are there moments of luck?
You do have to be lucky in a way, but I think you make your own luck. I’m thinking of when I wanted to persuade the mission leaders to do a closer fly-by of Enceladus because we’d seen an anomaly in the magnetic field data. The first fly-by was 1000 kilometres away above Enceladus, the second 500 kilometres below, I think. I went out to the JPL [Cassini headquarters at the Jet Propulsion Laboratory in Pasadena, California] to give a presentation to the icy satellites group. But I was in the right place to be lucky. I was jet-lagged to hell and just before the meeting I bumped into Jerry Jones, the person responsible essentially for driving the spacecraft, in the line waiting for coffee. I said, we’re seeing something in our data and we want to try and persuade the project to go really close on the third fly-by. He said: “That would be cool, I’ve always wanted to go closer to a planetary body than anyone else.”
In the meeting, some people said this is crazy, but Jerry said it’ll be fine – and we eventually agreed to reduce the fly-by altitude to just 173 kilometres. That’s when we saw the plume of water vapour coming off from the south pole, the hot spot and cracks at the south pole with organic material and dust coming out. Enceladus suddenly became the place to go.
Find out more about Cassini’s epic journey:
What were the particularly difficult times for the project?
There have been a few. When we lost the magnetometer sited at the tip of the boom, that made life really difficult. We now have to roll the spacecraft to calibrate our instrument properly. But it’s not just about equipment. We’ve had team members die: we had a really fantastic young scientist who was working with us on the internal planetary field, and he got cancer; we’re almost like a family, so that hit us really hard. And then we went through a time when the UK stopped funding Cassini. Luckily ESA took over our operations funding for a while, and the UK agency has since seen the error of its ways and started funded us again. But that was a really difficult time too.
And for you personally?
For me it’s been difficult that my parents didn’t see all this. When I was a kid growing up in South Africa, my dad built a 10-inch telescope. My sister mixed the concrete for the base. He ground the mirror. He had the telescope in the garden and I remember my first view of Saturn. You could just make out the little rings. We saw Jupiter too and the little spots of its four main moons, but I never thought I’d do what I do.
My dad died 12 years ago, and my mum a couple of years after that. They knew that I was taking over on Cassini, and they were chuffed about that, but they didn’t get to see how well things have gone. That’s one of my big regrets.
Is the end-of-mission party going to be a big one?
Yes, mostly because we want to thank all of those people who have never been in the spotlight. There are thousands of people who’ve worked on Cassini and its instruments over the years, right from the designing of them to building them, and they don’t get first author science papers or appear on television. These are people without whom we simply couldn’t have done the mission. So yes, we’re going to throw them a huge party.
How will you feel when Cassini is gone?
Weird, I expect. I’m not very emotional, at least not in public. But I gave a talk a few months ago and I showed a movie that JPL’s put together showing the lifetime of Cassini and how it’s going to end by burning up. I was standing there, blinking, hoping the lights wouldn’t go up. But I’m going to be brave. There’ll be a sense of regret, and also relief, because I am exhausted after 13 years. And pride, definitely pride.
- is professor of space physics at Imperial College London and Principal Investigator on the Cassini magnetometer. She will be talking about her Cassini experiences at New Scientist Live, the festival of science at London’s ExCel Centre, on 1 October.
A shorter version of this article appeared in print under the headline “Whole new worlds”
