Bonus Round at Saturn

April 15, 2008 7 mb MP3

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Narrator:  Extending a grand tour – of the ringed planet.
I'm JP with a podcast from JPL – NASA's Jet Propulsion Laboratory in Pasadena, California.  Ya' ever been on vacation and found out you got to stay an extra few days?  You know what a great feeling that was.  That's kind of how engineers and scientists on the Cassini mission feel right now.  The journey to Saturn was supposed to end in July 2008, but now NASA's extending the mission for two extra years.  Joining us is Cassini Project Manager Bob Mitchell of JPL.  Bob, let's start with a quick recap of the mission so far.

Mitchell:  OK. We launched in October, October 15 of 1997 and arrived at Saturn on the first of July of 2004.

Narrator:  Can you give us a few bullet points of some of Cassini's highlights so far, its major accomplishments and findings?

Mitchell:  Not necessarily in order of significance or importance.  Some very major discoveries of the ring, the dynamics of the rings, how the moons' gravity shapes the rings into the different gaps that we see.  Geysers on Enceladus have to rank near the top of the excitement of the discoveries that we've made.  Titan.  Titan is very different than we ever expected it to be.  Titan is a lot like Earth.  If you just replaced water with methane, there are a lot of processes on Titan that look a lot like Earth.

Narrator:  You mentioned Enceladus, that was a major discovery.  A quick recap of why that had everyone so excited?

Mitchell:  The idea of geysers coming out of such a small moon. It should be small, cold, inert, probably almost solid ice. So there should be no way that it could have the energy, the heat source that it would take to cause geysers to be erupting.  But there they are, you can see them very clearly in the images, and we know now that it’s those geysers that are creating one of the rings around Saturn.

Narrator:  So now you have this extension which obviously is exciting for you and the team.

Mitchell:  Yes, very much so.

Narrator:  And the spacecraft is healthy and doing really well.

Mitchell:  The spacecraft is doing just remarkably well. A few little things here and there, it's clear that we're not just driving off the showroom floor.  But considering how complex it is and the nature of the mission we're flying and how long it's been going, the spacecraft is doing remarkably well.

Narrator:  What will you get to do in this extension?  It's a two-year extension, which will take it to…

Mitchell:  It will go to July of 2010.  In that time we have 26 more encounters of the moon Titan, we have seven close encounters with Enceladus, the moon with the geysers, and we have three close encounters, one each of three of the smaller icy moons.

Narrator:  The three moons you mentioned, the little ones, are Dionne, Rhea and Helene.  There are so many areas to explore around Saturn that it's kind of like getting back to the vacation analogy, you have a certain amount of time, and you get out the tour books and you decide, 'What do I really want to see, what's on the B list, what's on the C list.'  Is that how you work it? 

Mitchell:  Partly.  Given that we wanted to be sure to go back to Titan and Enceladus a lot of times, then the orbital mechanics limits where we can go.  But yes, it's a lot just what you say, what are the areas where we didn’t quite got our appetite satisfied the first time around, where there are still questions that we want to get back to, so yes, very much like that.

Narrator:  And what are some of the specific questions you hope to have answered during this additional bonus time?

Mitchell:  One thing we'd like to understand better is just what's going on inside of Enceladus, what's causing, creating these geysers?  Is there liquid water in there?  What are the conditions, are there conditions in there that could be conducive to life?  Now we're a long ways from saying that we have found life on Enceladus.  But it's rather tantalizing based on what we've got so far to realize that these conditions could be very conducive.  For Titan, of course, we found methane lakes up around the north pole, this from the radar instrument.

Narrator:  And again, Titan's so interesting because of the analogies to Earth.

Mitchell:  That's a big part of it, yes.  But Titan is unique, if for no other reason, at least, in the sense that it's the only moon in our solar system to have an atmosphere, an atmosphere of any consequence.  And it's a very thick, dense atmosphere, and the atmosphere also is not that different from Earth's atmosphere.  It's 90-some percent nitrogen, and here on Earth we have a lot of nitrogen.

Narrator:  You mentioned orbital mechanics.  As you plan this extended mission, what are some of the can do's and absolutely cannot do's?

Mitchell:  We can't get too close to Titan.  Its atmosphere extends up to a thousand kilometers and more.  When we dip into the sensible atmosphere, this creates torques on the spacecraft that causes it to want to turn.  And if the torques get to be more than the spacecraft can handle, more than it can counteract, then it will cause the spacecraft to halt the sequence. Now that’s not catastrophic to the spacecraft, but it is very damaging to our objective of collecting the science data.  Another thing we need to be very careful of is on Enceladus, the scientists want to get in close to these geysers to better understand just what their composition is.  And we need to be sure that the environment for that is going to be a safe one.  The rings we have to be careful of.  We like to get in close to Saturn, but the rings represent a very clear hazard.  So these are things we have to keep in mind when we're designing our path.

Narrator:  What would be an analogy for those of us who drive cars here on Earth.  Would it be dodging dust storms, what kind of analogies could we think of?  Things to watch out for on the road?

Mitchell:  Objects lying in the road, objects that may have fallen off a truck would be very similar to our spacecraft flying along and encountering an ice particle near one of the rings.  The particles are small, but our relative speeds are very high, and so hitting one of these particles could be very damaging to the spacecraft.

Narrator:  Any other thoughts as you prepare for the extended mission?

Mitchell:  There have got to be a number of surprises yet waiting for us as we go through different regions around Saturn, as the seasons change, we're bound to find new, different, exciting things that we haven't even thought of yet.

Narrator:  We've been talking today with Cassini Project Manager Bob Mitchell of JPL.
You can learn more about Cassini and see a lot of pictures of Saturn, its rings and its moons at and .

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