A conversation with Jeff Cuzzi, interdisciplinary scientist for rings on the Cassini mission and researcher in the Planetary Systems Branch at NASA’s Ames Research Center in Silicon Valley.
Transcript
Host (Matthew Buffington): Welcome to NASA in Silicon Valley, episode 58. The profile of the planet Saturn and its famous rings is unmistakable and, this week, we’re talking to someone who has spent much of his career studying them. Jeff Cuzzi is the “interdisciplinary scientist for rings” on the Cassini mission, which is about to meet a fiery end, when the spacecraft dives into Saturn’s atmosphere on September 15. In addition to studying the composition, behavior and origin of the rings, Jeff helped plan the hundreds of orbits that Cassini made around Saturn, in order to capture the best, most interesting data. This included information on the planet, its rings and moons – like Titan and Enceladus – and some important surprises for the search for life in the solar system.
Now as a special treat leading up to Cassini’s decent into Saturn, stay tuned, or whatever it is you do for an audio podcast, because next week we will have another discussion about Cassini with Jeff, last week’s guest Chris McKay, and another NASA scientist, Dale Cruikshank. But for now, here to give us a tour of Saturn through Cassini’s eyes, is Jeff Cuzzi.
[Music]
Host: Thanks for coming on over, Jeff. We always like to start it in the same way. So first off, to learn a little bit about yourself, tell us: how did you join NASA, and what brought you to Silicon Valley?
Jeff Cuzzi:I came to NASA in about 1974 as a postdoc. I was working with a very famous scientist, Jim Pollack, who was in the space science division there. And I had done just a little bit of postdoctoral work before that, studying Saturn and the planet Mercury. I was a radio astronomer, so using these big dishes?
Host: Okay.
Jeff Cuzzi:You know these big radio dishes? Hooked up together. So I had been studying these objects. And just by accident, down in West Virginia, we were studying Mercury, which was during the day, and Saturn was up at night so we decided to look at it.
Host:Yeah.
Jeff Cuzzi:Nobody had ever seen the rings before, Saturn’s rings before, with the radio telescope. It’s just like they just weren’t there; it just looked round, like Jupiter. And we looked at the planet, and we saw something a little funny like in one place. And then just after I got back and I was reducing this data, Jet Propulsion Lab bounced for the first time this big, giant radar signal off the rings.
Host: Yeah.
Jeff Cuzzi:That was part of the puzzle that I was working on with Jim Pollack. So 1974, that’s when I got here, and we started working on the rings.
Host: So you’ve been obsessed with Saturn and the rings for quite a while?
Jeff Cuzzi:Well, who wouldn’t want to be?
Host: Was it like something ever since you were little, just obsessed with the stars and looking at that, or did you fall into it?
Jeff Cuzzi:Not really; just kind of fell into it. I was an engineer in college.
Host: Really?
Jeff Cuzzi:Yeah.
Host: Are you originally from West Virginia? Or are you California –?
Jeff Cuzzi:No, grew up in New York, went to Cornell, went to grad school at Cal Tech, went back to Massachusetts for a postdoc, and then came out here. And this is where I’ve been.
Host: Excellent. Did you join Ames as the postdoc? Doing that?
Jeff Cuzzi:Yes. Yeah, joined as a post doc, worked with Jim and did a few other things while I was here. Worked a little bit on SETI [Search for Extraterrestrial Intelligence] project when it was just getting started, and then had a two-year postdoc at Berkeley, and then they hired me as an actual Ames person in ’78.
Host: What were you working on then? Was it still focusing on planetary science and all?
Jeff Cuzzi:Oh yeah. All planetary science. In fact, they had got me started a little bit on space mission work. The division chief at the time, Dale Compton, had asked me to lead a new mission study for a Titan entry probe, which was the first study that had ever been done and I didn’t know anything about Titan at all.
But Ames had done all these probe projects like the Galileo probe to Jupiter was Ames, and the Pioneer Venus probes – there were four of them – went to Venus. That was Ames. So Ames had all this probe expertise, so I thought why shouldn’t we send a probe into Titan? Big, very fascinating moon around Saturn. And I said, “I don’t know anything about Titan, and I don’t know anything about atmospheres.” And Dale Compton said, “Don’t worry. Jim Pollack will help you out.”
Host: He’ll set you in the right direction.
Jeff Cuzzi:Right. So I worked on that. And as it turned out, we had the design that we came up with, we briefed [NASA] Headquarters on the design and they said, “Oh, this is great. We like this so much we’re going to give this to JPL for them to work on.” And so I thought, “Gee, that’s great.” And the guy, the engineer who I was working with, he was just aghast because all of a sudden Ames wasn’t going to be doing this project. Now JPL was going to be doing it.
And in the end, when NASA and the European Space Agency decided to work together on a Saturn orbiter with a probe to Titan, which is essentially Cassini, the probe was given to ESA to do. And ESA did a fine job, but they didn’t know much about probes. So for several years a number of Ames people were going over there to help them get up the curve on entry probes and entry technology and so on.
Host: It’s all very relevant to us right now. For the folks who are listening this is breaking the fourth wall slightly. We’re recording this right as Cassini just started its first of a series of orbits where it passed right in between Saturn and the innermost ring. And as I understand it, it’s going to do it I think 22 times before its final entry and burning up sometime in September of this year.
Jeff Cuzzi:Right.
Host: So, you know, when this is released, it’ll probably be a little bit after that.
Jeff Cuzzi:Yeah, that is funny. Right now is the culmination of this Cassini mission for which the planning started in around 1978 or ’79. So these things take a long time to come to fruition.
Host: Indeed it does.
Jeff Cuzzi:But here we are, and we have had a wonderful mission. Cassini was launched in 1997. It was approved by Congress in 1990, and then I joined the mission as what they call the “interdisciplinary scientist for rings” based on my rings background in 1990.
And since 1990 we had to build it, we had to launch it, we had to send it past Venus and then we had to send it past Earth, and there was a lot of controversy at that time about the plutonium onboard the spacecraft, and was that going to be a hazard or whatever? Then we had seven years in space.
We got to Saturn in 2004; there was a very, very critical burn that we had to do to actually put on the brakes if you like and keep us from just flying right on by like the Voyager spacecraft before had just flown by Jupiter, flown by Saturn, flown by Uranus, flown by Neptune, got a lot of wonderful data, but we wanted to go into orbit so we had to do this burn.
And we went into orbit, and now we’ve been going there – I think by the end of the mission we’ll be doing I think 290 orbits around Saturn in all kinds of different geometries, looking at the planet, the rings, the moons, sampling the magnetosphere from all different directions.
Host: So how many planets total did it end up visiting?
Jeff Cuzzi:Well, Cassini just went by Venus twice and the Earth once.
Host: And that’s all to gather speed, to get the orbit, in order to get launched further out?
Jeff Cuzzi:That’s right.
Host: Cool. So thinking back to when this whole concept even came up, and I’m sure people are pitching concepts to Headquarters. They probably say, “Nope.” Got to go back, try it again, modify it, edit it. What were you looking at as the original intent, the original mission for the space probe?
Jeff Cuzzi:Well, the original mission for Cassini, the original mission was there were two probes. There was a probe into Saturn like the Galileo probe, and a probe into Titan. So Saturn is like Jupiter – gas giant planet, hundreds of times the mass of the Earth. Titan is like the size of Mars, but it has an atmosphere that’s sort of like the same density as the Earth’s atmosphere, only maybe more so. Mostly nitrogen. So they’re very different environments.
Titan also has a lot of organic chemistry going on that was thought to have some clues about how life may have formed on Earth. So that was part of the goal, was to study Titan. We didn’t know how thick the atmosphere was at the time when we did that first probe study, so we had different options. We knew at the time we were designing this in the ’80s, Voyager had gone by Saturn already.
Host: So you knew there was something interesting there.
Jeff Cuzzi:So we knew there was a lot of really cool stuff to do with the rings. But with this little moon, Enceladus, which is only a couple hundred kilometers – it’s much smaller than our Moon, but it had a funny relationship with this big, broad ring around Saturn. So we knew there were a lot of really good reasons to go back to Saturn, and those were some of the goals.
Host: I’m thinking back to even this year, April of 2017, NASA did a big “water worlds” announcement. It was a culmination of data from Cassini, but also from other land-based telescopes. And I remember one of the images that stuck out in my head – it was an illustration, not really a photo – but an illustration of Cassini going through the plumes of Enceladus.
Jeff Cuzzi:Yeah, that’s a very cool graphic.
Host: Talk a little bit about that.
Jeff Cuzzi:Well, one of the major discoveries of Cassini that we actually didn’t make for a couple years almost I think, at least a year while we were there, was that Enceladus – it’s no accident that it’s in the middle of the E ring. It’s because it does have this molten south polar ocean, and it’s got these geysers and jets that are streaming away from the south pole and these geysers and jets start out with liquid water, but the water is salty. And it has organic material in it. And it has a whole number of these little silica grains and as the water comes out, it freezes and makes these little ice grains which then go into orbit and spread out into being the E ring.
So now we know, well – our hunch at the time was – and everybody was a little reluctant to say it – but maybe there is something like geysers or liquid water at Enceladus and that’s why we have this very peculiar E ring centered on Enceladus. It’s nothing like Saturn’s main rings. So that was one of the reasons for going there, and in fact that’s what we found. So now they’re learning about the composition of this subsurface ocean on Enceladus by flying the spacecraft through these flumes, and we have instruments onboard Cassini that can measure the composition of the dust. So like I said, organic, carbon-rich molecules with rings, like various complicated organics, and some salt.
Host: And then you mentioned the E ring. So for folks who may not be familiar, explain what you’re referencing in terms of – the location on the ring I’m guessing?
Jeff Cuzzi:Sure. When you think of Saturn’s rings, you’re thinking of the main rings. These are the rings that are kind of close to Saturn, and they’re very, very flat and thin in a vertical direction – well, from edge to edge the main rings are about as wide as almost from the Earth to the Moon. That’s how broad they are. But they’re only like 10 meters thick, so it’s like a piece of paper the size of Golden Gate Park. Very, very thin.
Host:Very thin.
Jeff Cuzzi:Those main rings are just composed of innumerable, icy mostly, particles of centimeters to several meters in size, all orbiting Saturn like little moons, bumping gently with each other and all that. The bumping is a little bit like the molecules in a gas, so when we think about the physics of the rings, it’s all about pressure and viscosity and self-gravity. So it’s like a fluid of particles, and they have certain boundaries between various regions of the rings that look a little different for one reason or another. And we call them the A ring, which is the outermost –
Host:Innermost? Oh, okay. Outermost. I’m going backwards.
Jeff Cuzzi:– of the main rings at Saturn. And then there is something called the Cassini Division, which is not really empty. And then there is the B ring, which is the most massive ring. It’s sort of the central ring. And then there is the C ring, which is the innermost ring, and those particles are darker and different in some compositional ways than the others. So those are the main rings.
Right outside the main rings there is a little, funny, curlicue-stranded, dusty ring called the F ring. Very narrow. And then if you go further rout there is something called the G ring which is like a rubble belt, and it’s got a little moon in it, and it’s maybe a couple hundred kilometers wide. Then if you go even further out to where Enceladus is, sort of four Saturn radii – the main rings are maybe two Saturn radii from the center of Saturn. The E ring is about four, and this is very broad, very diffuse ring. It spreads out to eight or nine Saturn radii, and it’s almost transparent. You can almost see right through it.
We know from the scattering properties of the particles that they are very different from the particles in the main rings, which are these centimeter- to meter-sized things. In the E ring they’re smoke particles. One micron in size, like cigarette smoke. They’re very, very small. And that was a puzzle, but now we know that’s because they froze out of this vapor that’s being ejected out of the pole of Enceladus into these little, tiny rings.
Host: And it’s forming it out.
Jeff Cuzzi:Right. And then they just spread around and form this diffuse ring.
Host: Let’s go back to a little bit of your day to day on working on this kind of stuff. How does that fit in? You come in, check your computer. What does it look like? For somebody who’s working on something like this, how does that go?
Jeff Cuzzi:Well, the way the mission has been organized, we had – because there are so many things that look at Saturn there. Right? And there are so many different disciplines.
Host: I would imagine. Yeah. Like teams and teams.
Jeff Cuzzi:Like I don’t know anything about the magnetosphere. So right. So we have the teams, which is built around the instruments. There is a camera team. There is an infrared team. There is an ultraviolet team. There is a dust-detector team. There are all these different teams. Magnetometer team. And they have their scientists on their teams. Each team has people who specialize in different things, so they all have a rings person maybe.
Host:Okay.
Jeff Cuzzi:So now because I’m the interdisciplinary scientist, we have a group that I’m the chair of, this group called the Rings Discipline Working Group, and there are discipline working groups for the satellites, the magnetosphere, and the planet. So we get together and we kick around everybody’s wish lists. By doing this, we’ve helped the project essentially design all these 200 orbits. We had to make all that up.
Host: Exactly.
Jeff Cuzzi:Where do you want to go, and for how long? So all those orbits had to be designed. So we had to do that, and then we had to say who gets to do what observations at what time on the orbit. So we do that. And then we allocate. And then it goes to another group that actually lays out these observations. So as the mission has gone on, you’re always planning a year or two ahead. So like maybe a night in 2002 or ’03 we were planning the first things we were going to do in 2004 and ’05. And in 2004 and ’05 we’re looking at the new data, but we’re also planning 2006 and ’07. And that went on through the whole mission, except now what’s fun is we’re done with the planning and we can just sit and watch all this stuff roll in.
Host: Nice.
Jeff Cuzzi:And by the way, anybody who is interested can log on or just check the Cassini website, which is saturn.jpl.nasa.gov, and you can look at the raw images as they come down off the spacecraft in real time.
Host: Just a couple days ago from when we’re recording this, it did the dive in between the innermost ring and Saturn itself. People were up at like 3:00 a.m. Pacific time waiting?
Jeff Cuzzi:It was more like midnight.
Host: Yeah. It lost connection for a certain amount of time and people were like, “Is it going to come back?”
Jeff Cuzzi:Yep. Yep.
Host: And it came back.
Jeff Cuzzi:It came back. There was a nice Twitter feed.
Host: It was a late night for you, then?
Jeff Cuzzi:Midnight. It wasn’t that late for me. But by midnight, they had the signal and there was a big room full of people down at JPL at von Karman auditorium, everybody cheering and happy.
Host: I bet.
Jeff Cuzzi:Then we can go to bed and say, “Okay, we’re good to go.”
Host: You were talking about the orbits and planning it out. I would imagine that that’s doing a lot of calculations, a lot of math, but then even when you know where you want to go, are you actually telling the spacecraft – is it jets? Is it doing things to try to maneuver, kind of tweak it in a certain direction? Explain that.
Jeff Cuzzi:Yeah. To point the spacecraft at all these different targets that we have, they have what they call reaction wheels. They’re like big flywheels, three big flywheels on the side, maybe each one is the size of a pizza or something like that. And they’re spinning very fast, and they’re heavy. Because – I don’t know if you ever tried this trick with holding a spinning bicycle wheel by the axis and trying to turn direction. It’s hard to do because of the inertia of the spin.
Host:It wants to get back.
Jeff Cuzzi:So what we can do to change the direction of the spacecraft. We change the voltage on these spinning wheels and slow one of them down or speed the other one up, and the spacecraft as a whole reacts, back-reacts, and it just turns.
Host: Tweaks. It kind of moves.
Jeff Cuzzi:Right. And it moves around. So we can point it in any direction we want. And because everything is bolted down to the spacecraft, we spend 15 hours looking around at this and that and recording all of our data on the recorders, and then we point and turn the whole spacecraft back to the Earth for nine hours and just sit there –
Host: To get the information?
Jeff Cuzzi:To get the information down. Right.
Host: Wow. How does that also play into how much energy? You mentioned the plutonium. That was powering?
Jeff Cuzzi:Right. Power. So most of the thing is run on electricity, and the way the plutonium works is it’s all forged into these vitreous ceramic golf balls. Think of a piece of a sink. It’s a ceramic, and it’s embedded in there. And they get hot, because the plutonium decays on an 84 year half-life.
And so they just get hot, and if you know what a thermocouple is, a thermocouple is a device with two different kinds of compounds in it, and when it gets hot, it generates electricity. So we just have all these thermocouples on all these little hot golf balls and it provides I think about 600 watts for the spacecraft. So over the time of the mission the power level has been very gradually going down. But that’s not what’s causing the end of the mission; that power will last for decades.
We have an attitude control gas that’s called hydrazine, and it just tweaks the trajectory a little bit when we need to, and we’ve got the main engine that we burn every now and then to change the trajectory a little bit more if we need to, which we do. And those are the resources we’re running out of. So at this point we’re running on fumes at this point, in those things. And that’s why we’re going to end the mission in September.
Host: Let’s talk about that final swan song. Even for you – are you hoping for some really cool data from going through these close orbits near that inner ring? Looking for some cool information I’d imagine.
Jeff Cuzzi:Yeah. Actually we’ve had 22 very close orbits already. What we call the “grand finale,” the first half of it we went grazing right by the very outer edge of the A ring that I was telling you about. Just inside the A ring and the F ring. We got some totally cool and brand new stuff in those 22 orbits. And then, what we just did was we fired a burn and we moved that crossing point, as you said, between the innermost ring called the D ring and the planet.
Host:Okay.
Jeff Cuzzi:Now we have 22 more of those. So now we can do a whole ‘nother kind of unique science. For instance, we’re so close to the planet now and the rings that the mass of the rings and the small irregularities in the mass distribution inside the planet affect the orbit of the spacecraft. And we can detect that when we track it.
We can measure the orbit of the spacecraft to within sometimes centimeters. And by these very, very small perturbations to the orbit we can measure the mass of the rings, and we can measure the internal distribution of the mass inside the planet. It’s never been done before, and it’s a very critical measurement to make. So we’re going to do that, and I can tell you more about that.
We’re also for the first time going to take some active radar, bouncing radar actually off the rings and doing a radio scan or profile with a resolution that’s comparable to our best images. But now this is actual radar bouncing off the rings, so it’s going to tell us all kinds of different things, again, that we’ve never seen before.
The other thing that’s totally new is because we’re actually crossing through the rings and all this dust that we’ve been worried about, the dust experiment can determine the composition of the ring material. Okay; we know it’s mostly water ice. But it’s – the rings are distinctly red. So we know it’s not all water ice. And what is that red stuff is a very big question that’s going to tell us how the rings were formed and maybe when the rings were formed.
So there are two different theories. One is that it’s good old fashioned rust, like Mars is red; the other is that it’s an organic material like carrots or tomatoes or watermelon are also red by organic molecules. So we should be able to tell the difference between those two things as this dust analyzer crashes through the dust.
Host: And at the very end of the mission, the end of Cassini is it actually is going to burn up into Saturn. Somebody may ask, “Why crash it in, instead of just letting it float off and try to milk it a little bit more?”
Jeff Cuzzi:That’s a great question. And it was decided early on – remember, I mentioned that Titan is of interest from the standpoint of exobiology, the formation of life. Now Enceladus also is because of its liquid ocean.
Host: Two hot targets out there that we want to look at.
Jeff Cuzzi:That’s right. So we don’t want to contaminate them with Earth microbes. Cassini was never really sterilized. The probe was sterilized. The probe did go down on a parachute to the atmosphere of Titan, but it was properly sterilized. Spacecraft was not sterilized. So we have to actually dispose of the spacecraft with prejudice, as they say, and that’s by burying it in the planet.
Host: I imagine that would be the worst case scenario. You send a future mission, rover or probe or something that gets out there, and we discover bacterial life… oh, that we brought there ourselves. That’s not going to be a fun time.
Jeff Cuzzi:That would be a disappointment. Right. Yeah.
Host: So for folks who have any questions for Jeff, we are @NASAAmes. We use the hashtag #NASASiliconValley. So if anybody has questions, they can start chiming those in to us and we’ll get back to you and bring it back together. Thanks for coming on over.
Jeff Cuzzi:My pleasure.
[End]