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IRA FLATOW, host:

This is SCIENCE FRIDAY from NPR. Im Ira Flatow.

Last week, an avocado-sized rock crashed through the roof a doctors office in Virginia. The rock was traveling somewhere around 200 miles per hour and you can imagine what happened. It tore through the ceiling tile, the carpeting. It banged a fist-sized hole in the cement, in the cement floor of the office. Was it some military exercise gone wrong? No. Actually, it was a meteorite, a half pound space rock that happened to sail through the atmosphere and hit in a place where someone actually noticed it.

Boy, did they notice it. Tiny meteorites pepper the Earth all the time and most go unnoticed, falling in the ocean, in the desert or places like that. There is no way to know very far in advance when theyre coming and they dont cause much harm, but what about the big ones, the ones that could wipe out a whole city - or worse, the planet? Well, my next guests were part of a panel organized to assess just how much we know about these potential civilian killers and what we could do if we detected them.

The bottom line of this report: the $4 million that the U.S. spends every year to search for these things is not going to cut it. If we want to be sure were detecting all the possible threats, especially the one with our name on it, what else can we do? Joining me now to talk about it are my guests. Michael AHearn chaired the Mitigation Panel on that report, which is basically the avoiding disaster panel. He is professor in the Department of Astronomy at the University of Maryland in College Park. Welcome back to SCIENCE FRIDAY, Dr. AHearn.

Dr. MICHAEL AHEARN (University of Maryland): Thank you, Ira. Glad to be here again.

FLATOW: Thank you. Faith Vilas chaired the Survey and Detection panel for the report. Shes also director of the MMT Observatory in Mount Hopkins, Arizona, and she joins us by phone. Welcome to SCIENCE FRIDAY, Dr. Vilas.

Dr. FAITH VILAS (Director, MMT Observatory): Thank you very much. Good to be here.

FLATOW: Thank you, youre welcome. Dr. AHearn, what was the conclusion of the report: too little too late, not enough?

Dr. AHEARN: Well, the conclusions are spread over a variety of areas. Basically, if we want find all the ones that could wipe out a city, we need much better facilities, and because in principle they can come at any time we need to start thinking now about how we would prevent them from hitting to the extent that we can. And not much thought has gone into that problem yet.

FLATOW: Do we have hardware, you know, any rocketry or whatever would we need to prevent one from hitting us?

Dr. AHEARN: We have the rockets that could deliver a payload to an NEO, but we dont know precisely what payload to send there because we know so little about the properties of the NEOs themselves.

FLATOW: Those are Near Earth Objects, the NEO.

Dr. AHEARN: Im sorry, yes. NEOs are Near Earth Objects, mostly asteroids, but some comets included also.

FLATOW: Mm-hmm. And Dr. Vilas, why do we know so little? Dont we have a survey going on that detects these things?

Dr. VILAS: We do have a survey going on that was started in 1998 and its a survey to find all objects that are about one kilometer in diameter or larger in size, and that survey was to detect 90 percent of the objects, the Near Earth Objects, that are about that size. And its just about complete, but if we want to look for the smaller objects, down to much smaller sizes, we need to upgrade our instrumentation, our telescopes to be able to conduct that survey. And thats the survey that we were also addressing.

FLATOW: Well, tell me your ideal survey. If you had I can give you the blank check book question. What would the ideal survey consist of?

Dr. VILAS: We concluded that it depends upon what your definition of ideal is. And if your ideal survey is to find these objects as soon as possible, then probably with a blank check we could send up a spacecraft to look for the objects from, for example, in near Venus trailing orbit with large ground-based telescopes augmenting the spacecraft results. But if constraint on funding is also in the works and its not urgent that you find all of the objects right away, if you can delay for, say, another additional ten years beyond what you might have achieved with the combined space and ground based program, then you could probably do the survey with well equipped and both - with a well-equipped and well-focused large telescopes only on the Earth.

FLATOW: Mm-hmm.

Dr. VILAS: But you can do it.

FLATOW: What about something like the Hubble, which is - sends back great pictures?

Dr. VILAS: The Hubble is not designed to find these objects. We need not only pictures, but we need pictures with time resolution. We need a large field of view. We need to be able to look at these quickly. These objects being so close to the Earth, when they come to the telescopes field of view, they are going to be moving so quickly that the Hubble probably is not the right telescope to do this type of work with. And the Hubble cannot look close to the sun. Its going to be required to stay away from the sun for - and a lot of these objects are located closer to the sun from our perspective, from the way we view them on the Earth.

FLATOW: Dr. AHearn, do you think its just a matter of time? I mean we I remember there was I wasn't around for the Tunguska Event, but wasnt that sort of either a comet or an asteroid hitting the atmosphere in Russia there, knocking all those trees down? Is it just a matter of time before we have another one of those or even something of a worse disaster?

Dr. AHEARN: Yeah. It is certainly only a matter of time before we have another event like the Tunguska Event. Its only a matter of time until we have another event like the impact that caused the extinction of the dinosaur. They are very different time scales, of course.

An event like the Tunguska Event, which flattened trees over a radius of something like a 10 to 15 miles, is an event that occurs, we think now, every few centuries. Only a few years ago, we would have thought it was less frequent than that. But new studies of how things blow up in the atmosphere have suggested that smaller things can cause an event like Tunguska than we had thought previously.

FLATOW: Mm-hmm. And what are our options? Lets say we would find something that size or a little bigger. What are our options for mitigating, for taking care of it so it doesnt hit us?

Dr. AHEARN: Well, the first option is to decide whether it is large enough that you need to prevent it from hitting or small enough so that its much more cost effective to simply evacuate the area where it will hit. So thats the first step. And thats a hard decision to make.

If you decide you have to change its course, prevent it from hitting, there are three different techniques that weve considered as appropriate, depending on how far in advance you know and how large the object is. For the really largest objects, the only system we know of that can change their orbits enough is a nuclear explosion. But those are fortunately the relatively infrequent ones.

The more frequent ones, if you have a long warning time, you may be able to pull them very gently for a long time, and just using the gravitational force of a spacecraft has been suggested as the right approach. For somewhat bigger ones or for ones where you dont have many decades of warning, just delivering a large mass into the object at high speed is an alternative and more efficient way to change the orbit.

FLATOW: Do you think, Dr. Vilas, that there is enough interest - enough interest in you know, we talk about building anti-missile systems for nuclear attacks it would seem that there might be the same sort of fear here to build some sort of system, or at least a detection system, to see where these are.

Dr. VILAS: I think that this is a problem, an environmental problem, that we are now capable of addressing. For the first time, I think humankind is able to address a particular problem that could significantly affect or, in the extreme, destroy humankind with enough knowledge we're beginning to have the knowledge to be able to address this problem, both to identify the objects that are coming in and to consider what method we should use, that Mike just described, to prevent these events from occurring or minimize their damage to the Earth.

And with the fact that we have this as the first time that we can do this sort of thing, and that we have the ability to potentially prevent an impact, unlike, for example, an earthquake or a hurricane, where we might even have a little bit of warning, but we can't prevent the event from occurring, I think there will become interest in this.

FLATOW: And there should be international interest. It's going to hurt everybody, right?

Dr. VILAS: I agree. It should an international interest, and it should be something that we, as a country, the United States, should work with internationally, and people internationally now are very interested in this particular problem.

FLATOW: Russia has this mission planned to divert an asteroid called the Apophis. I'm sure you're familiar with that one, if I'm pronouncing it correctly. It's supposed to come here in 2029 and them come back in 2036.

Dr. VILAS: Right.

FLATOW: And they feel that it's a significant enough threat that we should be talking about it or doing something about it. Do you agree?

Dr. VILAS: We're monitoring Apophis very carefully, and the last that I had understood was that the tracing its orbits significantly was showing that it was not necessarily going to intersect the Earth's orbit in 2036, even after it interacts with the Earth - you know, it's gravitational pull of the Earth changes its orbit a little bit in 2029. So, I don't know if this is a productive mission from the perspective of preventing a collision in 2036, but it could be a very instructive mission, both from the science perspective, from learning about this as a near-Earth asteroid, and also from learning something about an asteroid that's coming closer to us.

FLATOW: Would it not, Dr.�A'Hearn, be a useful thing to land a little ship on that asteroid, follow it along as it goes, learn something more about it?

Dr.�A'HEARN: You'd certainly learn a tremendous amount by having a landing on an asteroid. Depending on what mitigation method you're going to use, the key things you need to know are how efficiently momentum is transferred into the asteroid, how the motion of a spacecraft is transferred into the NEO.

It turns out that is controlled by the same set of properties that control the effect of nuclear explosions, as well. So in fact, we think that in terms of mitigation, the most significant advance would be made by sending an impactor to an NEO, which has a rendezvous spacecraft already there and which stays with it and monitors exactly how much the orbit is changed in addition to having the characterization that you get from an NC2(ph) mission.

FLATOW: All right, we're going to have to take a break. We'll come back and talk lots more about asteroids and impact. So stay with us.

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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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FLATOW: You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow. We're talking about searching for an asteroid with our name on it. We're talking with Michael A'Hearn, professor in the Department of Astronomy at the University of Maryland; Faith Vilas, director of the MMT Observatory in Mount Hopkins, Arizona.

Our number, 1-800-989-8255. Let's see if we can get some phone working here because a lot of people have questions about it, and let's see. Let's go to Matthew(ph) in Reading, California. Hi, Matthew.

MATTHEW (Caller): How you doing? Longtime listener, first-time caller. Real quick, I was just wondering: If a large asteroid were to impact a city, what's the likelihood it may be mistaken for a nuclear bomb and trigger a war. Take my answer off the air.

FLATOW: Good question.

Dr. VILAS: My first reaction would be that we would have enough warning of a large enough asteroid that we would know it's an asteroid coming into the Earth, and we would be studying it like crazy the moment that it came into the Earth, so that the likelihood is that we would know that it is not a nuclear explosion, assuming that everybody accepts that explanation.

FLATOW: But Michael, what if we send up a mitigation rocket to try to change the course of the asteroid, and it by mistake, because we don't know the exact parameters, it hits France, you know, instead of hitting us?

Dr.�A'HEARN: This is a very big issue, and it is the reason that international collaboration is crucial for any mitigation effort or even any mitigation experiments.

We can predict the track along which an NEO could hit the Earth pretty reliably long before we can predict exactly where on that track it will be. And an incomplete diversion of the asteroid would just move it from my country to your country. And that could easily be interpreted as a threat, which is why the early experiments have to be done collaboratively so that everybody understands what the other country is doing and agrees that it's all being done to best help everyone, not just a single country.

FLATOW: How do you convince people we need to spend the money on this? There's a chart in this study, averaging out the risks of death from various disasters. If you base this on the impact, the impacts pale in comparison to earthquakes.

You have 91 deaths compared to 36,000. So how do you convince people that we should be really concerned about these potential deaths on impact?

Dr.�A'HEARN: There are two issues. I'll just address the biggest one. The biggest one is that there's a difference between a few people dying every day and 1,000 people dying one time - once a year, which is why we probably spend a fair bit more money trying to prevent jumbo jet accidents than we do trying to prevent automobile accidents, which actually kill far, far more people.

So we worry much more about events that kill a large number of people at any one at a single time, than we do about routine, everyday events like falling off tall ladders.

FLATOW: Yeah, Dr.�Vilas, what would be give me a scenario for a step-by-step approach to setting up a detection system. How would you see that playing out?

Dr.�VILAS: I'm looking at a detection system for finding, in general, near-Earth objects.

FLATOW: Right.

Dr.�VILAS: The detection system would probably, depending upon what you want to expend in that direction, would consist of a large enough aperture, mirrored telescope. If it's on the ground, it's on the Earth, it's probably in the visible spectral region. If it's in space, you might be more efficient in the infrared, but you can do infrared or visible spectral region.

It has to have a large enough mirror so that it can collect light from faint objects. I'm going to optimize for fainter objects here, and it will be set up in a mode of operation, a sequence of operations or observing where it can look at a particular area, and then it will look at that area again after a small amount of time, to look to see if something has moved in that frame of the picture that they get, the snapshot of the sky - which will include stars, anything else in the sky. And if there's an asteroid, the asteroid has probably moved in that field with respect to the stars, which are all going to be in the same place.

And they're the sequencing was going to want to go back to those locations, confirm that an object has moved. From the trace we get of where the object has moved, we can tell roughly where it is in the solar system and how fast it is moving. And from the amount of light that we get from the object, we can determine roughly its size, by either making some assumptions about how much sunlight is reflected off of this rock - because that's what the light is that comes to us from the near-Earth object or the comet - and also if it's rotating. And it's very oddly shaped, as most of these objects are I nickname them potatoids most of them rotate and are very oddly shaped - we can determine things about their shape and their general structure. And then having done that with a larger telescope and identified this object as being its orbit, the first orbit that we identify as being going to potentially intersect the Earth, optimally we would be able to observe it with, say, a radar, like at the Arecibo Observatory or Goldstrum Observatory(ph). And they are able to refine the orbital elements, the track of the asteroid, enough that we will know where it is very finely and very precisely. We'll know much more about where it is, where it's going to go and whether it intersects our planet.

FLATOW: Let me see if I can get a quick question in before we have to go, Scott(ph) in San Francisco. Hi, Scott.

SCOTT (Caller): Hi. I'll make it a quick question. Thanks for the show. I teach eighth grade physics, and one of the things I use every year is "Armageddon," that movie with Bruce Willis where they go up and destroy the asteroid.

We always talk about what's possible and what's not in that movie. And one of the things they make a point of in that movie is talking about having to blow it up from the inside because a surface impact wouldn't do much. I was wondering if someone could speak to that regarding the real physics behind it.

FLATOW: Michael, you want to tackle that?

Dr.�A'HEARN: Well, if you want to blow it up, you basically just need to deliver more energy than the energy that's holding it together, which is the strength of the rock. And that will break it up, whether you deliver it on the surface, even with a kinetic impact, or some other way. We have natural collisions in the asteroid belt that break up the asteroids when one asteroid runs into another.

The trick about blowing them up that you have to worry about is to be absolutely sure that you either break it up into really tiny pieces, which is hard. There's usually often, maybe not always, but often a large piece left behind, and all those pieces need to disperse so that most of the pieces miss the Earth.

If you take a one-kilometer asteroid and break it up into five pieces, which would be roughly half-a-kilometer each in size, and they all hit the Earth, the net effect would be worse rather than better.

So we advocate the principle of do no harm and making sure that you're doing it safely. But all you basically, all you have to do is deliver enough energy to exceed all the energy that's holding it together.

FLATOW: Is there some point where you discover that it's too late to do anything, it's already too close? Is there such a point, or does that have to just be judged individually?

Dr.�A'HEARN: That depends on the size of the NEO.

Dr.�VILAS: And (unintelligible) go ahead.

Dr.�A'HEARN: Go ahead, Faith.

Dr.�VILAS: I was going to say and when we discover it. You know, if it's close to the Earth at the time, and the size, you know. If it's very close to the Earth at the time, there's nothing we could do to change that.

FLATOW: That would be your Plan B, moving populations, idea - that you were talking about before, Michael.

Dr.�A'HEARN: Yes, exactly.

FLATOW: This doesn't sound very hopeful.

(Soundbite of laughter)

FLATOW: You know...

Dr.�A'HEARN: Life is rough on Earth.

FLATOW: Well, you know, you say there is it's inevitable that we're going to be hit by a big object, like we have in the past, and yet we just don't know that we have the resources or the will to set up the preventive mechanisms and create the way to deal with it.

Dr.�A'HEARN: That's correct.

Dr.�VILAS: If we have enough warning that something is, an object is going to come in and hit the Earth, my faith in the human spirit is that we would have the will to do something to try to correct it.

FLATOW: All right. Well, we're going to leave on that upbeat note.

Dr.�VILAS: Okay.

FLATOW: Because we've run out time. I want to thank you very much for joining us. Faith Vilas is director of the MMT Observatory in Mount Hopkins, Arizona. Michael A'Hearn is professor in the Department of Astronomy at the University of Maryland in College Park. Thank you both for taking time to be with us.

Dr.�VILAS: Thank you.

Dr.�A'HEARN: Thank you, Ira.

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