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[no sound] >>INTERVIEWER: Mars is facing a close call on

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Sunday, October 19th, when a rare comet will pass by at

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an extremely close distance. And here to tell us more about Comet Siding

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Spring, from NASA's Goddard Space Flight Center in Greenbelt, Maryland, is

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NASA scientist Dr. Michelle Thaller. Thank you for joining us. >>MICHELLE: Hey,

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good morning, thank you for having me. >>INTERVIEWER: So what is a comet and why do we study them?

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>>MICHELLE: Well for millennia, comets have fascinated people. They almost look like stars

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with tails. And what the really are, are chunks of ice and dirt

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a couple miles across. And when they come close to the Sun, some of this material melts

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off and forms a gas cloud around the comet. The

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amazing thing is that these things are older than the planets of our solar system. There was a 

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time when the planets were forming, there were just small chunks of material coming through, 

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coming together. And some of this stuff got thrown out to the outer solar system. 

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Every once in a while, one of these things gets nudged and falls in, and what we have is

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a pristine part of the solar system billions of years old that we can study. 

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>>INTERVIEWER: What makes Comet Siding Spring so special,

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and will we be able to see it from Earth? >>MICHELLE: Now, Comet Siding

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Spring has come a long way. We actually think it began its journey about a million years

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ago. It began to drift very slowly and invisibly toward Mars. 

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It was only discovered about a year and a half ago, and at first it looked like it was going to 

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come right at Mars, maybe even collide with it. Now we know that Mars

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is going to go through the tail of the comet. And there will be an incredible view from the surface 

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of Mars. This comet will go across the entire sky. Unfortunately, the best

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view is from Mars. It's not visible with the naked eye here from Earth. 

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With a small telescope, especially in the southern hemisphere, you might have a decent

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view. In the north it's going to be very close to the horizon and very hard to see. 

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>>INTERVIEWER: How will NASA study Comet Siding Spring from Mars?

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>>MICHELLE: Well the amazing thing is we have a robotic fleet at Mars just ready

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to observe this comet. We have two rovers actually on the surface of the planet, 

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and we have as many as five different satellites that are going to be observing it. 

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All in all, there are 15 different satellites, telescopes, and programs

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that NASA's going to be using to observe this comet. And amazingly, the 

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MAVEN mission has just arrived at Mars. So the stroke of luck 

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was incredible. We launched MAVEN, it's arriving just in time to study this comet, 

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MAVEN is going to be able to look at some of the changes in the Martian atmosphere as

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the tail goes by and maybe even heats up the atmosphere a little bit. 

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>>INTERVIEWER: Is the comet dangerous, and will the satellites orbiting Mars be

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damaged? >>MICHELLE: Well one thing we do know is the comet will miss Mars. 

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However, it's going to be traveling very fast as it comes by. So, 

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as it goes by, the dust particles around the comet are moving at about a hundred thousand 

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miles an hour. And even a tiny little particle hitting a spacecraft at 

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that speed, that would be a pretty bad day for that spacecraft. So we've been modeling 

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where the densest part of the dust cloud is, and we think it's actually going to miss Mars. 

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However, we've adjusted the orbits of all of our satellites so they'll be 

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on the other side of Mars when the densest part of the tail goes by. 

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In some ways, we're going to be using the planet as a shield to keep our spacecraft safe. 

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>>INTERVIEWER: Sounds great, where can learn more?

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>>MICHELLE: Well to learn more, go to 

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the website mars.nasa.gov, 

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and you can learn about all of our programs 

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that are studying Mars, and 

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there's going to be wonderful news coming down about the comet. And hopefully

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in a couple days we'll even have some images, 

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some of the things that our observatories saw,

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all the way from Mars. >>INTERVIEWER: Dr. 

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Michelle Thaller, thank you very much for joining us. 

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>>MICHELLE: Thank you, very much. 

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