[no sound] [no sound] >>INTERVIEWER: Mars is facing a close call on Sunday, October 19th, when a rare comet will pass by at an extremely close distance. And here to tell us more about Comet Siding Spring, from NASA's Goddard Space Flight Center in Greenbelt, Maryland, is NASA scientist Dr. Michelle Thaller. Thank you for joining us. >>MICHELLE: Hey, good morning, thank you for having me. >>INTERVIEWER: So what is a comet and why do we study them? >>MICHELLE: Well for millennia, comets have fascinated people. They almost look like stars with tails. And what the really are, are chunks of ice and dirt a couple miles across. And when they come close to the Sun, some of this material melts off and forms a gas cloud around the comet. The amazing thing is that these things are older than the planets of our solar system. There was a time when the planets were forming, there were just small chunks of material coming through, coming together. And some of this stuff got thrown out to the outer solar system. Every once in a while, one of these things gets nudged and falls in, and what we have is a pristine part of the solar system billions of years old that we can study. >>INTERVIEWER: What makes Comet Siding Spring so special, and will we be able to see it from Earth? >>MICHELLE: Now, Comet Siding Spring has come a long way. We actually think it began its journey about a million years ago. It began to drift very slowly and invisibly toward Mars. It was only discovered about a year and a half ago, and at first it looked like it was going to come right at Mars, maybe even collide with it. Now we know that Mars is going to go through the tail of the comet. And there will be an incredible view from the surface of Mars. This comet will go across the entire sky. Unfortunately, the best view is from Mars. It's not visible with the naked eye here from Earth. With a small telescope, especially in the southern hemisphere, you might have a decent view. In the north it's going to be very close to the horizon and very hard to see. >>INTERVIEWER: How will NASA study Comet Siding Spring from Mars? >>MICHELLE: Well the amazing thing is we have a robotic fleet at Mars just ready to observe this comet. We have two rovers actually on the surface of the planet, and we have as many as five different satellites that are going to be observing it. All in all, there are 15 different satellites, telescopes, and programs that NASA's going to be using to observe this comet. And amazingly, the MAVEN mission has just arrived at Mars. So the stroke of luck was incredible. We launched MAVEN, it's arriving just in time to study this comet, MAVEN is going to be able to look at some of the changes in the Martian atmosphere as the tail goes by and maybe even heats up the atmosphere a little bit. >>INTERVIEWER: Is the comet dangerous, and will the satellites orbiting Mars be damaged? >>MICHELLE: Well one thing we do know is the comet will miss Mars. However, it's going to be traveling very fast as it comes by. So, as it goes by, the dust particles around the comet are moving at about a hundred thousand miles an hour. And even a tiny little particle hitting a spacecraft at that speed, that would be a pretty bad day for that spacecraft. So we've been modeling where the densest part of the dust cloud is, and we think it's actually going to miss Mars. However, we've adjusted the orbits of all of our satellites so they'll be on the other side of Mars when the densest part of the tail goes by. In some ways, we're going to be using the planet as a shield to keep our spacecraft safe. >>INTERVIEWER: Sounds great, where can learn more? >>MICHELLE: Well to learn more, go to the website mars.nasa.gov, and you can learn about all of our programs that are studying Mars, and there's going to be wonderful news coming down about the comet. And hopefully in a couple days we'll even have some images, some of the things that our observatories saw, all the way from Mars. >>INTERVIEWER: Dr. Michelle Thaller, thank you very much for joining us. >>MICHELLE: Thank you, very much. [beep beep...] [beep beep... beep beep... beep beep...] [beep beep... beep beep... beep beep...] [beep beep... beep beep...]