The 2013 Planetary Defense Conference
- Geoff Notkin
- Eileen Ryan
- Lance Benner
- David Trilling
- Amy Mainzer
- Detlef Koshchny
- Jay Melosh
- Sergio Camacho
- Alison Gibbings
- Alan Harris
- Brent Barbee
- Dan Mazanek
ANNOUNCER: What if one of the millions of asteroids in our solar system was on a collision course with the Earth? What would we do? How would we react? Hundreds of the world’s top engineers and scientists specializing in planetary defense have come together to tackle these important questions. Discover the latest alternatives to Armageddon on NASA EDGE.
CHRIS: Welcome to NASA EDGE.
FRANKLIN: An inside and outside look at all things NASA.
BLAIR: From the Meteor crater in Arizona.
CHRIS: We have special co-host, Geoffrey Notkin, of the Meteorite Men. Welcome.
GEOFF: Thank you so much. I’m thrilled to be here.
FRANKLIN: We’re here for the Planetary Defense Conference in Flagstaff, Arizona. Behind us is exhibit A of why we need planetary defense.
BLAIR: We’ll be talking to a number of experts on near-Earth objects.
GEOFF: We should get started on those interviews.
BLAIR: Let’s do it!
CHRIS: Let’s check it out.
BLAIR: The conference was an incredible think tank with asteroid experts. When they weren’t busy attending sessions or presenting papers, we had a chance to talk with many of them one on one. Chris kicked things off for us by speaking to Eileen Ryan about how we can discover potential Earth-colliding asteroids.
CHRIS: Eilene, tell me about NASA’s Space Guard program.
EILEEN: NASA’s Space Guard Program is a term we call the effort from many different observatories in the United States and some elsewhere in the world that look for objects like comets or asteroids that have orbits that cross the Earth’s orbit such that we might be concerned in the future they could hit us by us and them being at the same place at the same time.
CHRIS: We have a number of telescopes that are a part of this program?
EILEEN: We do. There are about three Discovery telescopes that survey the night sky looking for these objects and finding them. Then they pass on the information to a network of five telescopes that are called Follow-Up telescopes. Those telescopes will take those initial discovery and extend the positional information so we can accurately determine an orbit and then assess. Is this is something we’re going to have to worry about, exactly what the level of risk would be.
CHRIS: Follow-Up telescopes, could they be Discovery telescopes as well or are they limited by their size?
EILEEN: Many of the Follow-Up telescopes do a little bit of discovery on the side but they are primarily limited by their field of view. The survey telescopes have very large field’s of view so they can scan large patchwork quilts of the night sky. Where the Discovery telescopes have a smaller focus so they can do more accurate positional studies as well as trying to characterize the objects that are being discovered. When we find them, he have just their orbital system but you might want to know a little bit more about some of these…
EILEEN: Especially if it’s headed right toward you. Some of the information we would like to add to that which is a real advantage for a smaller field of view than discover is how fast is the subject spinning? What is it made out of? What’s its shape and other very important physical perimeters like that.
BLAIR: Lance, we’ve seen a lot of cool things at the Planetary Defense Conference. But you were talking during your session about actually imaging asteroids with radar. Can you tell e a little bit about what you’re actually doing to give us these fantastic images?
LANCE: There are two radar facilities in the world that we use for this. One is the Goldstone Deep Space Networks 70-meter antenna in California. The other is the Ariciebo Telescope in Puerto Rico, which is 305 meters in diameter. Both of them have high powered radar transmitters on them. They’re basically like big satellite TV dishes. They produce a radio signal that shoots up into space. Imagine that this is the asteroid in space and my hand is the radar dish. The signal goes up into space, hits the asteroid bounces off of it and reflects back down. Just as it’s about to come down to the ground, we switch from transmitting to receiving and then collect data for some period of time and then resume transmitting. It’s analogous to people turning a flashlight on and off or perhaps the pop on the flash on a camera except a flash goes off much, much more quickly. Depending on how we’re doing the transmitting, if the asteroid is close enough and the images are going to be really bright, we can basically modulate what we transmit and turn them into black and white images that can allow us to spatially resolve the asteroid. It’s an active form of observation. Most telescopic observations are passive, where you aim a telescope at something and measure what it is you’re collecting. In this case, we’re actively transmitting a radio signal that bounces off the asteroid and comes back to the Earth. We make an exposure and then transmit again and make another exposure. And keep on doing that as it moves and rotates.
BLAIR: Just like an asteroid photographer if you will.
LANCE: Uh yeah, you could think of it that way. We’re actually getting much more information than just that though because the radar measurements that we make enable us to estimate the asteroid’s velocity through its Doppler shift and also its distance. The measurements we can make are extremely precise. Our best resolution is 4 meters per pixel. To give you a sense of comparison, I’m about 1.8 meters tall. This is a little more than twice my height that we can resolve things.
LANCE: We do this on a regular basis for objects that are millions miles, if you would, away from the Earth.
BLAIR: Pretty impressive work from our ground observation stations, of course, not all observations are made from the ground. Chris talked to David Trilling about using orbital telescopes that track objects in space.
CHRIS: David, you gave a great talk today about the Warm Spitzer telescope. How do you use that telescope specifically in your work?
DAVID: We have this big program to observe about 600 near-Earth asteroids, which when the program started was about 10% of all of the known near-Earth asteroids. Of course, since then there have been more discovered so we’re not at 10% any more. For each one of those asteroids, we observe it with warm spencer and we measure the diameter and we also measure the reflectivity of the body. The reflectivity tells you about something about the composition. We’re basically, for each of these 600, measuring composition and size.
CHRIS: How do you find those near-Earth objects passing through?
DAVID: That’s actually easy. You point at the sky. The stars don’t move and asteroids move.
CHRIS: And you see that through video or is that just through data you collect?
DAVID: It’s through the data. You could imagine take your digital camera and point it out toward the road and take a picture every three seconds. You’ll see the cars drive past on the road. It’s the equivalent of that.
DAVID: Only, we’re seeing points of light that are moving. Some moving this way and some this way. You have to basically connect the dots. We do that in a pretty sophisticated way but that’s essentially the problem. You connect the dots. You know where this telescope is. You know where the sun is. You know where the dots are so you can calculate the orbit for this object.
DAVID: And using some other techniques you can look at the size and the orbit and we know the answer.
BLAIR: We have lots of ways to identify different objects in space. Amy Mainzer talked to our guest host, Geoff Notkin, about how NASA is using all of the data.
AMY: So, we’ve used our sample of about 700 near-Earth asteroids to extrapolate what’s actually out there. Because we were an infrared, survey telescope, we were sensitive to the very light-colored asteroids as well as the very dark-colored asteroids. That gives us a representative sample, if you will. If we extrapolate what we’ve learned from NEOWISE, this is what we found. There’s good news and there’s not so good news. The good news is that for the really large asteroids, the ones larger than a kilometer. These are the things very much like the dinosaur-killing impactor 65 million years ago. Ninety percent of those and maybe even more have been discovered to date. So, that’s great. That means there’s very little chance that there’s a civilization destroying, Earth impactor out there in the future that we haven’t already found. When we get to smaller sizes, which are still quite a bit larger in most cases than the impactor that just exploded over Russia in 2013. For those, the situation is not as good. We have not discovered nearly as many of those, for objects that are about a 100 meters in diameter, which is about the size of a football field. With NEOWISE we found that there are about 20,500 of these objects, larger than 100 meters. And only about 25% of them have been discovered to date. Clearly, there’s a lot more work to be done.
BLAIR: I’m sure everybody that saw the recent impact in Russia is asking the same question. How did we miss this one? Our friend from the European Space Agency explains.
FRANKLIN: As far as space situational awareness is concerned, how is it that no one was able to see the Russian meteor?
DETLEF: The Russian meteorite explosion had the distinct advantage that it came directly from the sun. Just like a good military pilot, this meteorite decided to come at us from a direction where we cannot look.
DETLEF: Luckily, it was small enough so that it didn’t do any real damage. People were hurt so that was bad. Windows were shattered but it didn’t kill anybody. But this object we could not have seen on that approach. We could have possibly have seen it on a previous flyby to our planet when it was flying away from the planet. But we heard yesterday at the conference from Paul Chodis that he did an analysis and over the last 30 years it would have been very difficult to spot this object.
GEOFF: One of the things I find most fascinating about the Chelyabinsk event is the time delay in this footage that we see. The fireball streaking by and then we’re looking at the smoke trail and then there’s the shock wave.
JAY: That time delay really is to be expected. It tells us how far away the explosion was. You could use the time delay almost immediately to realize it was a very high altitude explosion because it took almost two minutes between the fireball itself, the deposition of the energy in the upper atmosphere, and the arrival of the shockwave on the ground. We are probably all familiar with you counting seconds after a lightning flash till you get to the thunder. Typically you come up with a couple of miles distance. In this case it’s more like twenty miles distance because it deposits the energy so high in the atmosphere. This event is unusual that there was actually a sound. Most of the smaller fireballs we see, even if they deposit their energy at that high altitude, there’s no sound on the ground. In this case, there was so much energy released that the wave actually reached the surface in a strong form.
[Extreme sound & glass shattering]
JAY: You could hear the explosion. Windows were shattered and so on. It’s the magnitude of the event that’s really so unusual here.
BLAIR: I’m glad that the meteor in Russia didn’t have an impact like the one here in Arizona. Of course, this is a fascinating place to visit. And I was excited to talk about this massive crater with someone who knows just a little bit about meteors. Geoff Notkin, co-host of the Science Channel’s Meteorite Men, has spent his career traveling to remote locations around the world in search of impact sites and meteorites. When it comes to meteoritics he really knows his stuff. Geoff, it’s really exciting to actually be here in front of what Franklin calls Exhibit A for our need for planetary defense. But as I understand the meteor crater wasn’t always thought to be a crater. A lot of people thought it was a volcano. Can you tell us about the history?
GEOFF: You’re absolutely correct. The history of this site as it relates to meteoritics really begins around 1903 when Daniel Moreau Barringer came here. He was a mining engineer and also a visionary. He was a man ahead of his time. He was certain that this was a meteorite crater. And all of the leading geologists at the time said, No, it couldn’t possibly have been caused by rocks coming from outer space. It’s a steam blowout or a sinkhole or we’re not really sure what it is. But Barringer stuck to his guns and part of the evidence that strongly supported his viewpoint was at that time on the plains around the crater there were many strange twisted pieces of rusty metal that were later shown to be meteorite fragments that were the remains of the impactor that caused this extraordinary feature.
BLAIR: I don’t know much about meteorites but looking around you don’t see those big fragments but are there still smaller fragments around the crater?
GEOFF: There are doubtless still some pieces buried here. And back around the turn of the century and even into the 1930s and 40s, large pieces were found on the surface and some of them were actually melted down for the war effort during World War II, which was important at the time but seems tragic to meteorite researchers now. How much material was lost? By collecting fragments over the years, scientists have learned a lot about the impactor but it’s very important to note that this is a protected site. This is a unique site in the world. You cannot come here and collect meteorites. Anything that remains buried here will stay as it is so there will be something to study in the future. It wasn’t much more than a hundred years ago that nobody even thought that this was a meteorite crater. Look how far we’ve come. How far will we have gone in another hundred years when we’ll have new technology that will allow us to perhaps examine the crater and any remaining fragments in a different way.
BLAIR: It’s incredibly impressive but the one thing I wonder too, from your standpoint, when you look at something as impressive as this, what can we learn about it scientifically? What can we learn about meteorites and meteors and impacts?
GEOFF: We can learn we’re in danger. It’s a pleasant irony that the Planetary Defense Conference is taking place about 45 miles west of us at the moment. If you want any evidence that there is a danger of our planet or our civilization being destroyed by impacts from asteroids, here it is. This is a small one.
GEOFF: So, by studying this crater, by studying the fragments that were recovered in the past, we get an idea of the make up of meteorites that can cause the most damage. This crater was formed by an iron meteorite; a very dense piece composed primarily of iron with some nickel. It was traveling with such velocity and carried such mass with it that it didn’t experience atmospheric breaking like most meteorites do, most potential meteorites. It punched right through that atmosphere and exploded, thereby creating this gigantic and unique feature.
BLAIR: An impact on the order of what happened in Arizona would be devastating no matter where it hit. And that makes this a global issue. Fortunately, global concerns are definitely in Sergio Camacho’s wheelhouse.
BLAIR: One of the challenges we have is this is clearly a global issue. It’s not just a NASA issue but it’s a global issue. How are you involved in planetary defense from a global perspective?
SERGIO: One of the issues we will have to deal with is who is going to act in case there is a threat of an impact? If the impact is not coming to a nation that has the capability to do something about it, the first question is does anybody do anything about it? There is a feeling that there is a moral obligation if we can do something, we should do something. At the same time we want to have a universal understanding of what we’re doing so that it is not misconstrued that maybe intentionally somebody caused damage on someone else in case that deflection was not fully successful. As long as we haven’t touched it, it is what we call an act of God. The moment you touch it, you own it. Nobody is going to act if they’re going to run the risk of later being accused of improper actions, the liabilities.
BLAIR: Deciding to act or not at a point where we’re not really sure what we can do is also a difficult question. In some sense, you’ve got to tackle a few of these near-Earth objects and try to move them, or try to deflect them. Do you even know if you have the capability to do it?
SERGIO: It’s something that we have discussed and debated. On one hand we’re working on sensitizing the political establishment on what is being done, why it’s being done, the threat, the magnitude it could reach, and the fact that we’re looking at what to do about it.
BLAIR: I understand that you’re working on one of the many deflection techniques that are being proposed if we encounter a collision course with a near-Earth object. What is this technique that you’re working on?
ALISON: One of the techniques we’re putting forward is to use a contact list deflection of an asteroid through laser ablation. Where we are having a moderately sized or small sized spacecraft with an onboard laser system and that laser would shoot against the asteroid while the absorbed heat of the laser beam would enable the sublimation of the material. This sublimation immediately transforms the rocky asteroid into a big plume of hot gas and ejector from the illuminated spot. That’s enough to sublimate the surface creating a plume of ejector that is very much like a rocket exhaust in standard methods of rocket propulsion. And it’s that plume of ejector that acts against the asteroid over a long period of time to gently nudge it away, so gently push it away.
BLAIR: Laser ablation is an exciting approach to planetary defense. We were also able to learn how NASA, ESA, and astronomers around the world are sharing their ideas. Alan Harris, an astronomer working with NEOShield, talked about the three most popular strategies.
ALAN: One of these is the so-called kinetic impactor. It’s quite a simple idea. You take a spacecraft. It’s a relatively massive spacecraft. It might be a few tons in mass and you simply steer it at a very, very high velocity into the asteroid. It’s a big collision. It doing so you transfer momentum to the asteroid and you slightly change its orbit. You slightly change its track or at least its position. There’s another technique called the gravity tractor. It’s a technique that doesn’t involve actual contact with the asteroid itself. In that case you take again a relatively massive spacecraft and you rendezvous with the asteroid. You don’t collide with it you rendezvous with it. You bring the spacecraft up to the asteroid and until the spacecraft comes under the gravitational pull of the asteroid, which of course is very, very small. We’re talking about objects of a few hundred meters in diameter. They virtually have no gravity. It’s hardly measureable.
ALAN: But it does exist. There is gravity and that gravitational pull of the asteroid will tend to pull the spacecraft down to its surface. But the spacecraft has propulsion. It has engines. You fire the engines to simply keep a constant distance from the asteroid. And as you do that, very gently and gradually it has the effects of pulling the asteroid with it. It takes a relatively long time to do this but the advantage is you can very accurately control the change in orbit of the asteroid. In the case of a very large object, something for instance more than 500 meters up to a kilometer. It’s highly unlikely we’d have to deal with something like that. However, you never know. Statistically, anything is possible. If we were confronted with a large object and the kinetic impact wouldn’t be adequate, the gravity tractor certainly wouldn’t be adequate, we’d have to go for our third technique that we’re looking at in the NEOShield Project. And that’s called blast deflection.
BRENT: When you don’t have a lot of time on your hands, and you have an asteroid bearing down on Earth, that’s pretty much your final remaining option is to blow the thing to smithereens. That’s one of the things we’re studying as part of our NIAC, NASA Innovative Advanced Concepts study project. We’re designing a Hypervelocity Asteroid Intercept Vehicle. HAIV is the acronym. The idea is to give a nuclear explosive, which is what we would be forced to use in a short warning time scenario. These devices contain more energy per unit mass then chemical explosives or a kinetic impact vehicle. We leverage the fact that if you excavate a small crater in the surface of the asteroid and you can place the nuclear explosive in that crater the moment that it detonates, then that’s about 20 times more effective at coupling the energy of the blast into the body of the asteroid. You can couple enough energy into the asteroid body. How much energy you need depends on how big the asteroid is. But you can couple enough energy into the asteroid that it basically imparts velocity into all the mass of the asteroid and disperses it into a big cloud of debris.
CHRIS: Do you see this as the last line of defense for blowing up an asteroid?
BRENT: Um, sort of. We’re assuming that we haven’t discovered the asteroid even exists until roughly about 10 years from when it will hit the Earth. If we discover it 20, 30 some years or more before it’s going to hit the Earth, which is certainly of possible, then in that case we can use other techniques. But if we discover the asteroid 10 years or less before it’s going to make the hit, then we don’t try any of those other things. We go straight to the HAIV option that I was describing.
BLAIR: Not everything about planetary defense involves deflection or destructive methods. NASA is also planning a mission that will help us better understand asteroids. And Dan Mazanek took time to explain it in detail.
DAN: It was announced last week in the President’s budget roll out and the focus of it is bringing asteroid resources, material, hopefully to capture and return a small near-Earth asteroid and bring it back to Cislunar space using a solar electric propulsion spacecraft and a capture mechanism that would grab the object and contain it. Asteroids, in general, are a synergy for all the different things that NASA works on, science, human space exploration, planetary defense, obviously, we’ve got the Planetary Defense Conference. That’s important, and resources. For probably as long as I can remember and probably since the inception of NASA, we’ve always talked about utilizing space-based resources, living off the land. One of the fundamental issues with using in-situ resources is they’re typically done at the destination. If that destination is Mars, you have to get there. If you rely on those resources, there’s a certain risk inherent in that mission.
DAN: But just as we don’t drag a tanker truck behind us when we go cross-country, we rely on the gas stations along the way to allow us to make that trip. By bringing these resources back to Cislunar space, understanding how we can process and get valuable resources, like water, in particular, which can be used for anything from consumption by humans to rocket propellant, etc. We can actually bring those resources to the point of departure, utilize them, get comfortable with the operations so we can change this paradigm and basically be able to use space-based resources and feel comfortable with them.
FRANKLIN: We’d like to thank everybody for joining us here at the Planetary Defense Conference 2013.
BLAIR: And we’d like to thank Geoffrey Notkin again for being on the show.
GEOFF: Gentlemen, it’s really been my pleasure to work with you and to speak with so many fascinating experts in the field.
CHRIS: We learned so much about near-Earth objects this past week. It makes us realize just how small we are in the universe.
GEOFF: So, let’s take good care of our planet.
FRANKLIN: You’re watching NASA EDGE.
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