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Jupiter scientist: Galileo's plunge 'an extra bonus'

Torrence Johnson: Galileo's mission
Torrence Johnson: Galileo's mission "[set] the stage for the next generation of exploration."

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CNN's Frank Buckley discusses the success of the Galileo project with Torrence Johnson.
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CNN's Miles O'Brien on the exploits and upcoming demise of NASA's Galileo space probe.
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PASADENA, California (CNN) -- NASA's Galileo space probe plunged into Jupiter's scorching atmosphere September 21 after circling the giant planet and its moons for eight years.

Scientists sent the probe on its fiery descent to keep it from hitting Jupiter's larger moons, considered some of the most promising sites to search for life beyond Earth. CNN'S Frank Buckley discussed the final moments of the mission with Torrence Johnson, the top scientist on the project, at NASA's Jet Propulsion Laboratory.

BUCKLEY: Tell me, as you saw the last bits of data and knew that your baby was disappearing there, what was it like?

JOHNSON: Well, actually, a tremendous feeling of satisfaction for a job well done by the people that designed the spacecraft, flew the spacecraft and collected the data, and did the scientific analysis. It's been a fantastic mission, and spacecraft's essentially out of fuel now. We took some really good new data on the way in to our final plunge into Jupiter, and couldn't have been better, really, from that point of view. [There was a] little nostalgia for all the good times that we've had together with the flight teams over the years, but it's setting the stage for the next generation of exploration.

BUCKLEY: Let's talk about what this mission did. First of all, it was one that looked like it was doomed in the beginning, when your antenna didn't unfurl and it took a while to get the data stream coming back at a rate that you felt comfortable with. You guys somehow overcame that. I won't make you go through that again. But talk about the highlights of this mission.

JOHNSON: The highlights of the mission really have to do with the exploration of the entire Jupiter system. We put an atmospheric probe into the atmosphere of Jupiter for the first time, measured its winds, got the composition of the atmosphere, we took pictures of Jupiter and other data from outside of Jupiter, for the entire mission, found out where the lightning storms were. So we had just a -- one big piece of the mission was just the big guy himself, you know, Jupiter. And then we were looking at the huge magnetic fields and the magnetic domain around Jupiter, and then we had the four big Galilean satellites, four big moons around Jupiter.

And some of our biggest discoveries came there. We found that one of those moons, Ganymede, has its own magnetic field, just like the Earth does, which is still a bit of a puzzle, trying to figure out how its core can generate this magnetic field. And then we found evidence on Europa and also on Ganymede and Callisto for subsurface liquid oceans, salty liquid oceans that have really kind of changed our view for what sort of worlds these things are.

BUCKLEY: And of those three moons where you found this salty ocean, there's a belief that where there's salt and water, there's life. You were saying that Europa is the one that has the most promise. Why?

JOHNSON: Well, Europa may be the most interesting of these oceans for exploration because it's very similar to the conditions on the Earth. Europa's ocean contains about twice as much water as all of the Earth's oceans put together. So it's a huge volume of water. It's at a reasonable temperature, you know, just above the melting temperature of water, it's capped by an ice cap, and it may well have volcanic events on the surface of the rocky sea floor underneath that.

So we got conditions that are similar to what we find in the Earth's oceans and, in fact, conditions that many scientists think led to the formation of life and the evolution of life here on the Earth. And so we don't know that there's life there, but what we do know is that those types of conditions are things that we want to explore in the future to try to find out whether the presence of energy sources and the right organic molecules, water, will lead to life under those conditions, or whether life can exist in those places. So we're very interested in these things as targets for future exploration.

This is a 1989 file photo of the spacecraft Galileo being readied at the Kennedy Space Center.
This is a 1989 file photo of the spacecraft Galileo being readied at the Kennedy Space Center.

BUCKLEY: And when we say life, you're not suggesting that you'll drill a pipe into this ice, get into the ocean and have Jaws looking back at you or something like that?

JOHNSON: No. In fact, the sort of model we have for what might there that we would be looking for on future missions is something more like the microbial communities of heat-loving bacteria that exist on the hydrothermal vent systems on the Earth's ocean floors. And life, if it ever arose on Europa, may never have progressed much further than that. This might be -- we're kind of in the age of animals, if you will, on the Earth; Europa could be kind of a perpetual age of the microbe, basically, if the oceans actually sustained life.

BUCKLEY: And that's why you chose to crash Galileo into Jupiter, because you didn't want to potentially contaminate Europa? Is that right?

JOHNSON: That was one important aspect of it. We had several choices as to what to do with the spacecraft after the mission ended. One of them was just to, amazingly, leave it as space junk orbiting Jupiter, in which case it might have hit one of [the] satellites. And as a result of our discoveries, we thought that might not be a good idea. So we chose one of the other options we had, which was to send it into Jupiter, where we had already put an atmospheric entry probe into Jupiter, and things burn up in the atmosphere. So that's no problem.

And that also allowed us to get much closer to Jupiter with our science instruments than we had before. So we think we got an extra bonus of science by doing it this way, also.

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