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Deep Impact: Mission Science Q&A
Tiffany Nail:
Dr. McFadden, welcome.

Dr. Lucy McFadden:
Thank you, Tiffany.

Nail:
Our first question for you is, would you tell us about your role in the Deep Impact mission?

McFadden:
Certainly. I'm a member of the science team. There are 13 scientists who are, who have the responsibility of designing the experiment, saying what we have to, what we want to accomplish in our mission. We worked with the engineers to design the spacecraft to make sure it gives us the data that will address our scientific questions, and then we also plan the sequence of observations that the instruments and spacecraft will require. I'm also responsible for the education and public outreach component of the mission.

Nail:
What is it that we hope to learn from this mission?

McFadden:
We have three primary scientific objectives. One is, the comets are the oldest and coldest material in the Solar System. So we are using the comets to look back in time and determine what the Solar System was made of at the beginning. Secondly, there is a theory that comets brought water and organic material to Earth that later evolved into life. So we're very interested in determining the nature of the carbon-bearing compounds in the comet. And then finally, what we learn from the comet will help us understand how to take avoiding action should a comet -- not Tempel 1, but another one -- should a comet in the future be on a collision course with the Earth.

Nail:
What makes this mission possible from a technical point of view?

McFadden:
Well, first of all, we have a pair of spacecraft that we're sending into space toward comet Tempel 1. They travel together for six months, but when we get to the proximity of Tempel 1 on July 4, the impactor will separate from the flyby spacecraft and it will head toward the comet on a collision course with the comet. It will be carrying a camera and will take pictures of the comet as it gets closer and closer to us, as the Ranger spacecraft did in the 1960s. Now, the impactor spacecraft is a spacecraft on its own, it carries fuel, it has computers, and it has an antenna that will relay the images to the flyby spacecraft that then sends the data back to the Earth through the deep-space network. Let's see. And finally, other technical components...Oh, there's a big mass of copper, there's 100 kilograms or 220 pounds of copper on the impactor spacecraft, and that makes us, allows us to open up a big crater that we will observe with our cameras.

Nail:
I have a question for you, when you mention the copper. Why copper, why not sending an explosive device up there?

McFadden:
Well, first of all, using the copper and the mass of the impactor is a lot simpler, it's a lot less expensive. So it's a technical advantage to use the mass and the motion of the spacecraft to create the impact and the explosion. Secondly, we chose copper because it's not very reactive. It won't react with the comet itself, and the emission features, the fingerprint, the compositional fingerprint of the copper, will be observable in our spectra, but we'll be able to subtract it out of the data. So we can keep them separate from what's the comet and what's the impactor.

Nail:
When is Deep Impact expected to reach Comet Tempel 1?

McFadden:
Our impact date is July 4, 2005, of this year. We will hit the comet at 6 o'clock universal time, that's the time in Greenwich, England, and it'll be 2 a.m. here on the East Coast, 11 p.m. the night before on Jan. 3 on the West Coast, and 8 p.m. Hawaiian time.

Nail:
Very early for us. Will amateur astronomers be able to contribute or participate somehow?

McFadden:
Oh, absolutely. We have two programs for amateur and observers with small telescopes. We are encouraging amateur astronomers to go out and observe the comet. We have a Web site that is designed for the amateurs: http://deepimpact.umd.edu/amateur. There, we have star charts and directions on how to find the comet. You have to go star-hopping to actually find the comet in the sky. We also urge you to join with amateur astronomers and astronomy clubs if you can, because they have a lot of experience. Then we have the small telescope science program, for people who have telescopes and digital, what we call CCD cameras or video cameras that can record the event, and we're asking the small telescope observers -- some of whom are amateurs and some are professionals -- to observe the comet as often as they can. They have access to their telescope whenever they want it, whereas the large telescopes, professional telescopes, have to compete with time for people who want to observe the rest of the universe. So the small telescope science program is also designed for scientists to help get us complementary information and monitor the behavior of the comet.

Nail:
So that's what you envision this mission leading, to further comet research in the future, what you mentioned just now?

McFadden:
Well, yes. What we learn from this mission, from the inside of the comet, will help us -- I know we're going to have new questions, so it will help us and stimulate our questions about, that we can't answer from this mission. So the next step after the Deep Impact mission would probably be a sample return mission from the surface of a comet. We have the Stardust mission, which is flying through the head of comet Wild 2 and that's bringing stardust that has left the surface to the Earth. And then there's a European mission, Giotto, that will land on the comet and give us complementary data. So all of the missions sort of feed into each other, help us design the next step as science is incremental.

Nail:
Space fans around the world have submitted Deep Impact questions to our NASA Direct Question Board. People are really interested in this mission! Are you ready to answer some of their questions?

McFadden:
Sure. Let's give it a try.

Nail:
Alright, let's get started. Our first question comes from Junichi from Niihama-city. Why did you choose Tempel 1 as the target of the Deep Impact mission?

McFadden:
Well, Tempel 1 was in the right place at the right time. It's a short-period comet, it comes close to the Earth so that we can see it from the Earth with our ground-based telescopes. But it's not too close, so you don't have to worry. It also has cometary activity, but not too much cometary activity, so that we know that when we get close to it, when we flyby at about 300 miles distance or 500 kilometers, we'll be able to see through the gas and dust and see the surface of the comet. So it has a number -- oh, one other point. It rotates slowly so that when we hit it, we will be able to observe where the impact hit and it won't rotate out of view before we get to make our follow-on observations. So it has the right properties and it's in the right place at the right time.

Nail:
Junichi would also like to know, how deep a crater will the impactor make on Tempel 1?

McFadden:
Well, this is a scientific experiment and we actually don't know. The depth of the crater depends on the structure of a comet, that's one of the things we're hoping to learn from our measurements of how deep the crater is. But nevertheless, we have some expectations. We think it's going to be about between 100 and 200 meters wide, that's about the size of either a football field or a football stadium.

Nail:
Junichi asked us, can he watch the breathtaking crash phase live on the Web site or on television?

McFadden:
Well, we will be bringing back, we will be releasing our images as soon as they get back. So, NASA TV, there will be broadcasts on NASA TV of the first images. Then we will work through the night to piece together the images from the impactor and create an animation that will be ready for the first press conference on the early morning of July 4.

Nail:
Our next question comes from Paul from Rockville. What will we learn about the mechanical properties of the comet, such as strength, damping, etc?

McFadden:
Well, when we hit the comet, we'll be watching what happens to the debris that is sent out from the comet. If the comet is very porous, sort of like corn starch, for example, most of the energy of the impact might be absorbed and not much debris would be ejected from the crater. So we'll watch to see how much debris is ejected. If it is denser, but still weakly held together, not very strong, then the debris will shoot out really far and travel a great distance. So again, we'll watch for the shape of the debris that leaves the crater. Then the third case is, maybe the inside of the comet is glued together. Maybe it's really strong. If that's the case, then we predict that the impactor will hit and the top will be blown off, the debris will go straight up from the impact, and this is sort of like what happened when I was microwaving a squash the other day and I didn't pierce the skin. It blew the top off the squash.

Nail:
Nathaniel from Monsey: How will Deep Impact collide with the comet?

McFadden:
Well, actually, I'm glad you asked that question. The comet will actually run over the impactor. We have timed it so that the spacecraft gets to the point and travels right in front of the comet just before it hits, and at this point, the comet is king in the Solar System. It's at its point where it's moving the fastest and it's going to just bowl over and destroy the impactor.

Nail:
Sounds like a very violent mission. Peter from Basel Swiss: How fast is the impact speed?

McFadden:
At the time of impact, the impactor will be traveling at 10 kilometers per second. That's 23,000 miles per hour. Now, how fast is that? A jet airliner travels at 500 miles per hour and a bullet travels at about 1 kilometer per second. So, it's 10 times faster than a speeding bullet.

Nail:
Thomas from Jonesboro: What is being used to "blast" a hole into Tempel 1 to figure out what comets are really made of?

McFadden:
Well, we're using the mass and the motion of the impactor to create the explosion. There are no explosives onboard, it's purely passive, kinetic energy of mass and motion.

Nail:
Jesser from Salem: Is there a possibility that doing this mission might set the comet off of its orbit and might do damage to neighboring planets, stars, etc...?

McFadden:
Well, Jesser, that's our most frequently asked question. And fortunately, there's no chance of -- well, let's see, how do I phrase this? The change in the comet's orbit is miniscule. We can't really measure it. So, there is a slight change because we're adding energy to the comet, but it's not perceptible and it's not significant. So, there's nothing, there's no risk to any other planet or the Earth. None of the debris will come, none of the debris from the impact will get to Earth at all.

Nail:
Junichi from Niihama City: How far is the Comet Tempel 1 from the Earth in Astronomical Units?

McFadden:
Well, at the time of impact, it's at Point 9 AU, and an astronomical unit is the distance between the Earth and the Sun. So that's about 83 million miles away. See, it's at a safe distance, so no one will get hurt.

Nail:
Vince from Galt: Will we be able to observe the comet at the time of impact with amateur telescopes?

McFadden:
Oh, absolutely. And we need you to go do that, we want you to go do that. We have set up our Web site, deepimpact@umd.edu -- oops, I'm giving the wrong Web site -- for amateur observers, we have a Web site called "The Night Sky Observers." This is a network of observers and they have a Web site at Jet Propulsion Laboratory which is on your screen (http://nightsky.jpl.nasa.gov/ ). So you can join the network of amateur observers to find out where you can see the comet.

Nail:
Robert from Pennsylvania: How will copper affect the spectra of the impacted material?

McFadden:
Well, when the impactor hits the comet, the impactor will be destroyed and all the material of the impact will heat up and some of it will probably show a spectral signature, which are emission lines in our spectra. So the copper will be there, but we know where those lines are and we'll just subtract them out of our data and interpret what's left.

Nail:
Jimbo from Palm Beach Garden: Some scientists have suggested that the mysterious Siberian blast was caused by an anti-matter comet. Have the worst case scenarios for our probe encountering an anti-matter comet been considered?

McFadden:
Well, first of all, comets are made of matter. There is no evidence that there is any anti-matter in the Solar System and comets are not made of anti-matter. So that's not a problem, that's not something that we had to look into.

Nail:
Junichi from Niihama City: After the Deep Impact Mission turns out to be totally successful next year, will you apply "this kind of method" to another celestial body for exploring in the near future?

McFadden:
Well, as a matter of fact, we have a mission called "Deep Interior," which is similar to Deep Impact but it flies to an asteroid and we'll study the interior composition and structure of an asteroid. But that mission hasn't been approved for funding yet, so it's just our idea at the moment.

Nail:
Fred from Chicago: Is this mission also a test to see if we can destroy or change the course of comets and meteors?

McFadden:
No, not really. We're just, we're interested in the nature of the interior of the comet, and we will not really be moving the comet much out of its orbit. It's very, it takes a lot more energy to do that than the energy of this impact.

Nail:
George from Scotland: The recent large earthquake in Southeast Asia reportedly shifted the Earth's axis by one inch. Does this mean that you need to recalculate the Deep Impact launch trajectory?

McFadden:
Well, that's an interesting fact. There is, we can theoretically calculate how the earthquake in southeast Asia changed the rotation rate of the Earth and how, how much it shifted the orientation of the North Pole. However, those are theoretical calculations. We can not measure how much it changed the rotation rate, and it will take time to determine the orientation. So we did not change our, we did not recalculate our launch time. If we need to make changes, if we find we're off course, we'll use our rockets to make any changes to make sure we stay on course.

Nail:
Junichi from Niihama City: How long is the duration for the impact spacecraft to observe the crash?

McFadden:
The impactor will spend 24 hours as an active spacecraft. So it'll work for 24 hours.
Nail:
Ang Yi Ci from Singapore: Will Deep Impact be destroyed by debris flying out of Tempel 1?

McFadden:
No. We've designed a sequence where the flyby spacecraft will move into shield mode and protect itself from any of the debris. So we have an engineering design to keep the spacecraft safe.

Nail:
Ken from Princeton: Will the impact be visible using a moderately sized backyard telescope?

McFadden:
Yes, indeed. The comet will be about ninth magnitude, where a sixth-magnitude object is just visible with the naked eye. So you will need binoculars or a small telescope to see the comet before impact. We don't know how bright it's going to get from the impact, so maybe it will brighten to the point where it will be visible without a telescope, but certainly with a telescope.

Nail:
That would be great. David from Wichita Falls: Will amateur astronomers with small telescopes be able to detect any brightness changes in Tempel 1 after impact?

McFadden:
Yeah. I hope so, and we need you to go out and observe and tell us what you see, because we really don't know how bright the comet will get, so we need observers to go out and monitor for us. Nail:
David from Stafford: For amateur astronomers on Earth, how much and how quickly will brightening of the comet occur after the impact with Deep Impact? Also, could the brightening exceed expectations?

McFadden:
Well, it would be spectacular if it exceeded our expectations because then more people could see it in the night sky. The brighter it gets, the more likely more people will see it. So again, we really don't know. We have predictions that we need people to go out and observe and verify whether our expectations were correct or not.

Nail:
Our last question comes from Junichi from Niihama City. There is a hypothesis that life on Earth originated from another heavenly body, including comets. Is the Deep Impact spacecraft able to analyze the life form or that similar to chemical compounds of the materials around the nucleus of Comet Tempel 1? I'd like you to comment on this hypothesis.

McFadden:
Well, it is indeed true that we have a, there is a hypothesis that water and organic material were the precursors of life as we know it. Our spectrometers can not measure the actual complex carbon compounds, the DNA and RNA that indicate life. However, we're very interested in the simpler carbon compounds that will tell us something about what they, what the building blocks of life were, indeed. So we are very interested in any of the carbon-bearing minerals and compounds that we detect.

Nail:
Thanks so much, Dr. McFadden, being here in our studio with us today.

McFadden:
Well, thank you for having me. I enjoyed it.

Nail:
And now we have some prizes to give away! Our top two questions from the question board will receive a mission gift pack, and everyone else who had their question answered during our show will also receive a prize.

Today's winners are George from Scotland and Junichi from Niihama City. To integration experts Mike Stelzer and Tom Shaw, Delta weather officer Joel Tumbiolo, NASA launch manager Omar Baez and Dr. Lucy McFadden, thanks so much for being with us and sharing your knowledge.

And to all of you who joined us for today's show, stay tuned to NASA Direct for the launch of Deep Impact on a mission to collide with Comet Tempel 1! Thanks for watching.