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Transcript of the Debate

Transcript of the Debate

Carl Murray, Zibi Turtle, and Brigitte Hesman
From left: Carl Murray, Zibi Turtle, and Brigitte Hesman

Linda Spilker: Let's take a sneak peek at three scientists discussing their favorite targets. It'll give you a chance to decide which one is your favorite.

. . .

Brigitte Hesman: Hi. My name is Brigitte Hesman. I work at the University of Maryland and I'm based at Goddard Space Flight Center working on one of the instruments on Cassini called CIRS. It's a spectrometer that looks at Saturn's atmosphere and determines its temperature and composition. I spend a lot of time studying weather on Saturn.

Zibi Turtle: I'm Zibi Turtle. I'm from the Johns Hopkins University Applied Physics Laboratory and I work with the camera on Cassini, studying primarily Titan, its surface, the lakes and seas on its surface, and its weather, the big rainstorms that we've seen from time to time on Titan.

Carl Murray: My name is Carl Murray. I work at the astronomy unit, Queen Mary University of London, and my interest is in rings. I'm a member of the imaging team. Rings are essentially all composed of small satellites and they move around Saturn, so I'm interested in the way they move, and how they interact with the icy satellites, the big ones, the small ones, so that's what interests me.

Zibi: Okay, so we need to discuss the different observations coming up to figure out which one is the highest priority, to choose between them because we don't have infinite resources.

Zibi: So, you have a Saturn observation.

Brigitte: Yes, we have a Saturn observation where we're going to be going over top of the north pole of Saturn, and when we go over the north, we're going to take a lot of camera images with a wide camera and a narrow camera, where we're taking a look at this really neat feature called the Hexagon which a lot of people don't understand because it has this six-sided feature that just looks like it's standing there. They're trying to understand the wave-like nature of the Hexagon. In addition, at the very pole, some of our colleagues have discovered a beautiful hurricane right at the pole of Saturn's north just recently. We want to get some more narrow images to try and understand the cloud depths and what's going on in the hurricane.

Carl: Is this a kind of unique observation? Will you get another chance to do this?

Brigitte:The inclined orbits are coming to an end ...

Zibi: Because Cassin’s in a tilted orbit, right?

Brigitte: Yeah. Cassini is not going right along the equator right now. It's going up and over the poles. We won't do that for very much longer, and without these type of images at this point, we won't necessarily get another good view.

Zibi: So, for the same reason, because we're approaching over the high northern latitudes, that's exactly the same reason why this is such a good time to look at Titan. Because for Titan, it gives us a view of the north polar region, which is the region on Titan where we see lakes and seas of liquid hydrocarbon on the surface. And we don't see those anywhere else on Titan.

Brigitte: And what are those images going to show you about the lakes? Are they going to show you what they're made of? Or are they going to show you how big they are? Or are you going to be able to see if they have changed?

Zibi: Yes, so the observation we have planned will take the camera, we'll take a mosaic of almost the entire disk of Titan. It will show the high northern latitudes, and that will show us the locations of the lakes and seas, their sizes and their shorelines. The spectrometer will also be taking data at the same time, and that will give us compositional information about the surface and about the lakes and the seas.

Brigitte: That will tell us what it's made of.

Zibi: That will tell us what it's made of, yes. And then the camera images and the spectrometer images will be able to tell us the shapes of the lakes and the seas. And one of the things that's very important is to see if those change over time. So, at the very end of the mission, as planned, we'll have another chance to look at the high northern latitudes, and given three years in between, we'll be able to see if anything has changed on the surface. And things may well change on the surface, because as summer is approaching, Titan's atmosphere is heating up at the high northern latitudes, as Earth's does in the summer, and we expect big storms to occur. Storms with methane clouds and methane rain pouring out onto the surface, flooding the channels that we see on the surface, eroding the channels, and flowing down into the seas and the lakes. So this observation of Titan is important because it gives us something to compare an observation a few years later, too. We haven't seen any storms yet. All the computer models actually predict that we should have had storms, but predicting weather on Titan is apparently just as hard as predicting weather on Earth.

Carl: And storms on Saturn.

Zibi: Yes.

Brigitte: And all our storms are on Saturn right now.

Zibi: So we haven't seen any storms yet. This observation would give us a good "before" picture, of Titan's north polar region to compare if we get storms between now and three years from now when we'll have another opportunity to look at Titan. And then we can compare those observations and see if anything has changed, and then see if three years from now we see rivers flowing on the surface, as opposed to empty river channels.

Carl: Okay. Well, I think we should be looking at rings. Saturn is the ringed planet, after all. The strangest ring of all is this F ring just outside the main ring system. We saw with Voyager it's just bizarre.

Brigitte: What makes it bizarre?

Carl: Good question. That's one of the things we want to understand. Which is why we should be doing the ring observations. Partly it's due to there's a moon on either side, Prometheus and Pandora, and they have a gravitational effect on this ring. We think they're also exciting, there's objects we can't see, sort of like a dark matter at Saturn, things we can't see, and they're getting excited and they're colliding with the core of the ring, producing these jets.

Jets of ring material, coming off the rings.

Carl: Jets of ring material, yes. Some of them are kind of small, as we call these "mini-jets", other quite large ones, several hundred kilometers, going out from the ring. So we want to understand this. Because these are collisional processes going on. Objects colliding. All sort of –

Brigitte: They are all bumping into each other.

Carl: All bumping into each other, you know, and it's almost sort of fender bender velocities. So, we'd like to see that, and there's kind of no wasted image of the F ring. It's just so bizarre, wherever you're going to look, we've got a special – just like you all have special observations – our one is we're going to stare at one side of the rings, and essentially just stare at the material and wait for the material to come underneath us. The one thing we don't have is weather. So I think we're lucky in that respect. We could just do without any weather.

Brigitte: Weather is very complicated. We all need to try and understand it. That's why we really have to focus in on the north pole of Saturn and try and understand what these storms are doing, and why do we have a hurricane at a pole?

Zibi: And with Titan, the models that we use, the computer models that we use to study Titan's atmosphere are models that have been designed to study Earth's atmosphere, and if we can apply them to Titan's atmosphere and predict Titan's weather, then that tells us that the physics that's in the model is correct. So these observations of Titan, if we see clouds starting to form, which we expect it may happen as northern summer comes to Titan, then we use those as tests of the computer model, so right now there's a big question mark why we haven't seen the clouds yet, so that's one of the reasons that observing Titan right now is very important.

Carl: With the F ring, we have a situation where the modeling actually came first. The modeling was able to predict structures that were being produced by Prometheus. Prometheus dragging out material. We looked at all the Voyager observations, and never saw anything like that, but the model predicted they should exist, and then when Cassini gets there, we see them, which is a big tick for modeling, to be able to predict that these things existed. But we're learning. There's still things we don't understand.

Linda Spilker: Now you had a chance to see what passionate scientists think about their favorite target. So, read up, learn about them, and pick YOUR favorite. We look forward to reading your essays.


CIRS – Cassini's Composite Infrared Spectrometer (an instrument that measures heat to figure out what Saturn's rings and moons are made of)

spectrometer – a scientific instrument that splits light into different colors, like a glass prism, or a raindrop creating a rainbow

composition – what something is made of

imaging team – people who use the Cassini spacecraft to take pictures of Saturn and its rings and moons

Hexagon – a six-sided shape

wave-like nature – appearing to have the properties of a wave (e.g., a light wave or sound wave)

hydrocarbon – an organic compound made entirely of hydrogen and carbon (such as methane or ethane)

methane – a chemical compound (CH4 ) that is the main component of natural gas

F ring – one of the outer rings of Saturn

Voyager – Voyager 1 and Voyager 2 are two NASA spacecraft that launched in 1977. They explored Jupiter, Saturn, Uranus, and Neptune.

Prometheus and Pandora – two shepherd moons of Saturn. Shepherd moons are small moons of Saturn that orbit near the rings and help to shape some of the rings.

gravitational effect – the effect of gravity (how one thing pulls on another)

dark matter – material that cannot be seen, but that has gravitational effects (pulls) on its surroundings

jets – trails of material in Saturn’s F ring caused by a shepherd moon passing nearby

collisional processes – things that occur causing objects to collide and as a result of these collisions

fender bender velocities – slow speeds (causing crashes that are not big enough to cause major damage, just two things gently bumping into each other)

computer models – computer programs we use to show what might happen under certain conditions

northern summer – when it's summer in the northern hemisphere, it's winter in the southern hemisphere