Planetary Radio: Space Exploration, Astronomy and Science - Defending Earth From Asteroids

Episode Date: March 15, 2004

Defending Earth From AsteroidsLearn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

. Deflecting the Big Rock with our name on it, this week on Planetary Radio. Hello everyone and welcome back. So a Tyrannosaurus, a Triceratops and a Pteranodon walk into a bar. The Pteranodon is just about to say something about the T-Rex's hat when they all get hit by a 10-kilometer asteroid, and that's that. Do we humans have a better chance? First we have to find that rock.

Then we have to deflect it. Stay tuned for our conversation with near-Earth object expert Alan Harris. We'll get a little Shakespeare on What's Up with Bruce Betts, and guess who's back and readjusting to Earth time. Here's Emily with Q&A. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, In 1974, Mariner 10 went into a solar orbit so that it flew by Mercury every second Mercury year.

Is Mariner 10 still visiting Mercury? Mariner 10's last known flyby of Mercury took place on March 16, 1974, and the last of the gas for the Attitude Control jets was depleted eight days later, ending the mission. Mariner 10 is no longer tracked, so we don't know its location. Presumably, though, it continues along its orbit of roughly two Mercury years. However, it no longer actually visits Mercury. How does that work? Stay tuned to Planetary Radio to find out.

And we thank Emily for her great work with the student astronauts over the last several weeks. Reading about Sputnik launched Alan Harris into a space science career. He went straight from grad school to 28 years at the Jet Propulsion Lab. Recently retired from JPL, he's still very busy working with the Space Science Institute, mostly on the topic of near-Earth objects, or NEOs. Last week, he dropped by Planetary Society headquarters to talk about nothing less than the defense of planet Earth.

Alan Harris, thanks, first of all, very much for joining us on Planetary Radio. It's a pleasure to be here. So how long have we got before the big rock hits? Well, probably a long time. As I often tell people, we're all going to die, but probably not from the asteroid. And that's been one angle of the research that you've been doing, I think, which is that I guess it has emerged that the threat is maybe not quite as great as we've been told for the last few years.

Well, as we have refined our estimates of the number of objects and the size of objects, the threat has, or estimate of the threat has gone down. It's true. objects, the threat has, or estimate of the threat has gone down. It's true. When Gene Shoemaker first made estimates of the population, he guessed about, well, didn't really guess, he estimated about 2,000 objects a kilometer in diameter or larger. That's about two-thirds of a mile in diameter.

And we now believe that number is closer to about 1,000, perhaps 1,100. So that's almost a factor of two smaller. Which is good news for earthlings. Well, yes. And you mentioned Shoemaker, of course, and one of the affiliations that you've had with this place, we're sitting in the Planetary Society, is I guess you've served on the selection or evaluation panel

for our Shoemaker NEO grant program. Yes, I have, for the last two years. Also, Gene Shoemaker was a teacher and mentor of myself. I took classes from him. I've known him or knew him ever since the mid-'60s. What led you in the direction of studying asteroids, and in particular the class called Near-Earth Objects, the ones we have to worry about?

Well, Gene had a great deal to do with that, too. In fact, he was asked to organize a couple talks for an AGU meeting, American Geophysical Union, back in about 1985 or so on natural hazards. And Gene featured impact hazard as one of three. The others were earthquakes and volcanic eruptions, which, of course, are more common to physical hazards. That was practically the beginning of serious consideration of the impact hazard, and Gene and I gave a couple of talks in that session. Just a couple of weeks ago, you were a major participant, delivered a couple of presentations in a conference not far from us in Orange County, California.

Right near Disneyland, yes, right down the street. How appropriate, near Space Mountain. Talk about that a little bit. Was this a regular sort of gathering, and what was everybody talking about? These gatherings are what I would call occasional gatherings. Different organizations sponsor different ones. This one was sponsored by the American Institute of Aeronautics and Astronautics. Others have been sponsored by various other organizations in the United States and in Europe.

And there's no regular schedule. It's not like an annual meeting. It's just kind of an ad hoc affair. This one here followed by about a year, one that was held in Arlington, Virginia, last year, and considered the matter of mitigation primarily. That is, what would you do if you found an impacting asteroid? How do we defend ourselves? How do we defend the planet? Yes. Now, the first day we did discuss, and one of the papers I gave had to do with refining the hazard as we know it now,

but the main issue that they were spending the remaining three days of the conference on was what to do about it. And I think we've seen a little change in attitude over the years. The opinion now, I think, is that we have well enough defined the hazard. We may be able to tweak the numbers a little bit, 10 or 20 percent or 30 percent on the frequency of impactors. But the most important thing now is to find the one, if anyone exists, that has our name on it. Beyond just having a fair idea of the hazard, that's all that really counts. Refining the second decimal place in the percentage hazard is really not important.

The most important thing is to find if there is actually one out there. So clearly, even though the hazard may not be quite as great as we thought it was a few years ago, it's still very real. Yes. Our current estimate is that a kilometer diameter object that could have global effects, that a kilometer diameter object that could have global effects, that is affect perhaps a billion people on the planet, might happen about once in a million years. Our previous estimate was maybe a couple times in a million years.

So it's a little lower, but that's still not zero. It's a lot more often than the one that killed the dinosaurs. Let's go back to that second presentation, the paper that you presented, which was quite specifically on this topic of this conference a couple of weeks ago, how do we defend the planet? I looked at the program online, and there were all kinds of presentations, obviously different approaches to doing this, pushing it out of the way, blowing it up a la Armageddon,

and I guess you tried to address this, what might work and what won't. Yes. The subtitle of my topic was What Makes Sense? And I think that is a major concern that we had over the many years that this has been discussed now. In some of the early conferences, people were talking about building nuclear bombs and going out and blowing up a couple of asteroids just to be sure we could do it. Made good movies. It made good movies. Well, I take it back.

It didn't really make good movies. It doesn't make terribly good sense, however. For one thing, simply politically trying to get any kind of approval or change of existing treaties and so on to conduct nuclear experiments in space is just not practical, nor do I think is it wise. Carl Sagan, when he was involved in this shortly before he passed away, discussed a matter called the deflection dilemma, or what he named the deflection dilemma. And by that he meant that the cure might be worse than the disease.

dilemma. And by that, he meant that the cure might be worse than the disease. If you built an arsenal of missiles to have at the ready in case an asteroid comes your way, on average, you have thousands and thousands of years to wait. And the probability that someone might misuse such a facility more frequently than you would need it means that you actually are increasing your risk overall from a different cause. And so it would not be wise to build such a system. That's one of the systems that does not make sense, in my opinion. Do you remember a few years ago when there was some excitement about this, and Edward Teller, the father, the proud father of the H-bomb, said,

this is why we have to build bigger H-bombs? Yes. Yes, he attended one of the meetings we had was in Livermore, and he was very much present at that meeting. And he proudly announced that militaristically for bombing populations on the earth, it doesn't make sense to build a bomb bigger than 100 megatons or so because if you go larger than that, it just blows out of the atmosphere and no more damage occurs on the ground.

It just blows a bigger plume. Like the Shoemaker-Levy 9 Comets hitting Jupiter, you get this big plume that shoots out into space, but it doesn't do any harm outside of the range of the explosion. So Edward Teller made the point that bomb labs could very easily build even a gigaton bomb. Wow. If there was any reason to have it.

But there wasn't a military reason to have it. But if the asteroids needed it, he could produce it. And he'd actually be happy to do it. Probably he would. Oh, God. One of the great characters of the 20th century. We're getting to the point where we should take a break. Maybe we should go ahead and do that.

20th century. We're getting to the point where we should take a break. Maybe we should go ahead and do that. And then when we come back, talk about some of these considerations of what would work, in your opinion, to defend the planet, if not blowing them to kingdom come. Okay. Dr. Alan Harris is our guest. He is an asteroid expert of the Space Science Institute of Boulder, Colorado, although in your case, La Cunada, California. Yes.

And we will be back with more of Dr. Harris right after this. This is Buzz Aldrin. When I walked on the moon, I knew it was just the beginning of humankind's great adventure in the solar system. That's why I'm a member of the Planetary Society, the world's largest space interest group. The Planetary Society is helping to explore Mars. We're tracking near-Earth asteroids and comets. We sponsor the search for life on other worlds,

and we're building the first-ever solar sail. You can learn about these adventures and exciting new discoveries from space exploration in The Planetary Report. The Planetary Report is the Society's full-color magazine. It's just one of many member benefits. You can learn more by calling 1-877-PLANETS. That's toll-free, 1-877-752-6387. And you can catch up on space exploration news and developments

at our exciting and informative website, PlanetarySociety.org. The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. Our guest, Alan Harris, who is here talking to us about asteroids and that particular class of asteroid known as NEOs, the near-Earth objects, the ones that we do have to pay a little bit of attention to and maybe think about how we're going to deal with the one that, as heEOs, the Near Earth Objects, the ones that we do have to pay a little bit of attention to, and maybe think about how we're going to deal with the one that, as he put it, has our name on it. Let's talk about that.

We mentioned in the first half of our conversation that you were at this conference and that this conference did focus on what do we do about them. What are the options and what should we be most attracted to as a solution? The first obvious possibility, of course, is nuclear explosions. That is the highest energy that we can deliver for the least weight. And so that, as the expression goes, doesn't take a rocket scientist to think of that one. Other possibilities, though, Jay Malosh of the University of Arizona talked about focusing sun on an asteroid to evaporate a small spot

of it and get a similar type of rocket recoil effect by creating a jet with the rocky material of the asteroid itself. Another possibility that was discussed extensively would be to launch a high energy electric propulsion system

to the asteroid, and the same propulsion system that would get this rather massive spacecraft there could then be used to attach to the asteroid and push on it over a period of a decade or so and actually push it out of the way. But you do need that kind of lead time for a solution like that. Almost any solution would require a fair lead time. For one thing, it may take years to even refine the orbit calculations enough to know that it definitely is or is not going to hit the Earth. You don't want to start pushing on it before you know you need to. Yeah, which is kind of an economic decision that we'll come back to.

I want to talk about that. There was a very clever idea that Ed Liu, one of the astronauts who spent time on the space station about six months ago, came up with right during the conference, in fact, and that was that people were concerned about the problem of attaching the spacecraft, the asteroid, in such a way that you could push on it, and the thing is spinning, and so you attach to a spinning object, you're not pushing in one direction, and so on and so forth.

There are many, many problems with pushing on it. Well, the conclusion he came to was that if you have this roughly 20-ton spacecraft, the asteroid's gravity pulls on the spacecraft, and, of course, the spacecraft pulls back the same force, gravitational force, between the two. So if you just snuggle up alongside this asteroid a few hundred meters off the side and park there, station keep, keep these electric propulsion engines on pushing, you don't even have to touch the asteroid. This is the ultimate green solution.

You don't even touch the asteroid. You just gently pull it aside. Isaac Newton would be so thrilled. Yeah, we were all captivated by this idea. It's really clever. And so this actually solves a lot of problems. It still amounts to taking a very big spacecraft out there a long time in advance with some big, expensive propulsion systems and so on.

But it is a very cute solution. Huh. So does that capture pretty much the solutions that were discussed that are under consideration, or is there anything that's even more out there? Oh, there were a number of other ideas I don't recall. All of them, one of them that comes to mind is a kinetic impactor, which the deep impact mission, which NASA is about to conduct in the next year or two, is a small scale of the same idea.

You just take a big sandbag, if you like, or ball of whatever, and park it in the path of the asteroid some orbits ahead of time and let the asteroid slam into that, and that impact then changes the trajectory a little bit. And that would deflect the asteroid. and that would deflect the asteroid. It's far less controlled than this electric propulsion system, which is exquisitely controlled in terms of being able to move exactly the way you want. But a big sandbag could be very cheap, and it turns out that parking a sandbag in the way of an asteroid that has your name on it is pretty easy

because you know the orbit crosses the Earth's orbit. You don't really have to go any distance. You just have to move a little ahead or behind the Earth's orbit a little bit until you catch some previous orbit pass and slam into it. I want to talk a little bit about what that leads me to think about, which is our orbital mechanics, basically, which we understand really well. But we had an episode happen, what, almost during the conference, where we were told some astronomers who were within hours of wondering

if they should call up the White House and say, we need to be scared. But then, of course, it turned out, nope, it's okay, it's near miss. Well, it was about a month before it just turned out that the news got out through a talk that Clark Chapman gave. I think it is misinformation to say that astronomers are thinking to call the White House. I mean, this is the kind of idle speculation one has when waiting to get an airplane and wondering if the plane's going to crash. Of course, idle thoughts cross minds in a moment of tension, but no one was seriously considering calling the White House.

Interesting, because the mass media obviously decided to make it a better story. They tried to make it a better story. Yeah, I see. However, during that night, what happened was the asteroid that was detected on a very short period of one-hour observations was thought to be possibly a very close-by object. Instead, it was a very distant asteroid, very much different. An analogy I've made on that is it's like driving down the road, and you look out the window of your car, and you see a bird flying,

or you see a spot in the sky. And it could be a bird quite close to your car pacing you. Or it could be an airplane way off in the distance, and its velocity has nothing to do with your car's speed. It only looks like it's pacing you because as the trees go by and so on, it kind of stays in the same spot in the sky. So you're left with an ambiguity. You don't know if it's a bird up close or if it's an airplane in the far distance

until maybe you look with binoculars or something. This is exactly the problem we had with that asteroid, is that it mimicked a little rock up close coming right at us. But in fact, it was a very large or much larger asteroid at a great distance. And as soon as it was observed the next night, it was immediately clear what it was. So it says something about the importance of looking for these things. Yeah. And doing a better job of looking for them can be expensive.

Doing a good job of deflecting them could be vastly more expensive. With only a couple of minutes left, it would appear, and I know this is something you've thought about, that there are economic decisions to be made here in dealing with these threats. Yes. To me, the cost of mounting a space mission has to be way more than the kind of insurance value if you don't know one is coming your way. That equation changes completely the second you discover one.

If you actually discover one coming your way, it's worth almost anything. I will be right there on the doorstep of the weapons labs right away to get this thing out of my backyard. But before you actually discover it, it really doesn't make sense to me to spend a lot of money on mitigation schemes. However, finding them, of course, is essential, and finding them down to some size level has to make sense. Finding the kilometer objects makes overwhelming good economic sense.

Perhaps it's sensible to find them even down to 200 or 300 meters in diameter. With only about a minute left, what would you recommend that we should be doing right now, next year, five years from now, to improve our chances? Improve our chances? Of survival, of finding these. The next step, I think, is a more ambitious survey to go to smaller sizes. Not only does that have value for the impact hazard, but it has fantastic scientific value for astrophysics

and a host of other research causes, discovering Kuiper belt objects, discovering all sorts of weird denizens of the outer solar system. It would be very, very exciting science in addition to addressing the hazard. We don't often get to talk about issues that are literally life and death here, unless it's life on Europa. This is a little closer to home, and it's made this absolutely fascinating. And I'm sure there are going to be other developments. I hope we can talk to you again in the future.

Yes, thank you. Alan Harris has been our guest, Dr. Alan Harris of the Space Science Institute, Boulder, Colorado, in La Cunada, California. We will be back with more, Bruce Pett specifically and his What's Up segment, right after this from Emily. Stay tuned. I'm Emily Lakdawalla, back with Q&A. Mariner 10 is still on a two-Mercury-year orbit, but it probably no longer flies by the planet. Mariner 10's orbit takes it close to the Sun at some times and far from the Sun at other times.

It only approaches Mercury's distance from the Sun once every two Mercury years, and at other times it's farther away, closer to Venus's orbit. The last time that the spacecraft encountered Mercury, its orbit was changed just a little bit, and the spacecraft also gets tugged on by Venus. The net effect of these little tugs has changed Mariner 10's orbit just enough so that when it approaches Mercury's distance from the Sun, the planet isn't there to meet the mute spacecraft. The next time a spacecraft will visit Mercury will not be for another three years, when Messenger will fly by the planet. The Messenger mission reached a milestone last week when the completed spacecraft was shipped from Goddard Space Flight Center in Maryland to Kennedy Space Center in Florida in preparation for its May launch.

Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Bruce Betts, we're going to have fun today with the trivia entries, trivia contest entries. Everybody stay tuned. It is time for What's Up with Bruce Betts, the director of projects. Yeah, I'm excited too. Let's talk about the night sky first. We've got our four friends, the planets up there that are very easy to see still.

You can see Venus is the really bright thing in the west after sunset, and Jupiter is the really bright thing in the east after sunset. And in between them, you can find Mars to the upper left of Venus. And on March 20th, it will actually be just three degrees from the Pleiades, and we'll be near the Pleiades that whole time. Kind of a neat thing to look at in binoculars. Pleiades, a little star cluster of fun. You also can see Saturn high in the sky,

also at sunset, in Gemini. And sort of mid to end week, if you're really crazed and have a really clear view to the horizon in the west, you can actually pick up the fifth naked-eye planet, Mercury. But if you don't this week, stay tuned. It will be back for the next couple weeks, and you'll get a better view of it higher

in the sky, and you'll be able to see all five naked-eye planets at one time. Woo-hoo! Nice job. Very succinct, and I love the Pleiades. Aw. I just do. I've always loved the Pleiades. Probably because they're the only ones I can find.

But anyway, my favorite is Starcluster. My only Starcluster. I may change the trivia contest. Anyway, this week in space. Oh, actually, I want to say one other thing because I forget to mention this, and it's hard for a global show like this. Another really neat thing to see in the night sky are satellites passing overhead, things like the International Space Station, lots of satellites up there.

But your predictions for your area are very localized. One place you can go on the web is www.heavens-above.com, but there are other websites where you can do predictions for your areas. Go see them. This week in space history, March 18, 1965, Alexei Leonov makes the first ever spacewalk for 10 minutes aboard Voskhod 2.

On to random Space Fact! A solar flare that lasts several hours is so powerful that it could provide the energy needs of the United States for about 10,000 years. Of course, if we could harness it, which we can't, but kind of neat. That's why it's a random space fact. All right. It's just as well because, you know, we'd have all those companies that are now in Iraq not figuring out how to make money off of it. So a little political humor here on Planetary Radio.

We now return to our regular format. On to the trivia contest. You're chomping at the bit. The trivia question phrased kind of complexly. You're chomping at the bit. The trivia question, phrased kind of complexly. One of the moons of Uranus has chevron-shaped features on it that Voyager 2 showed us, and it was named from a character in a Shakespeare play. What Shakespeare play was it?

Many, many answers. I don't know whether it's because spring is almost upon us, but we have all this renewed interest in the trivia. No, it must be the T-shirts. Of course it's the Planetary Radio T-shirt prize. They are exciting. They're popping up in fashion magazines everywhere. No, I'm not going to give you the winner.

A lot of them at the Oscars. I noticed that, and they were all getting out of hybrids. I'm not going to give you the winner yet because I think we need to mention this one because this may be the funniest entry that we've ever gotten. The person got it right but was not the randomly chosen winner. And this person did get the right answer, which I'll have to tell you, I guess, to tell this. Miranda is the moon, the play is The Tempest.

But this person says when this play was first performed in 1611, it was not called The Tempest. It was written in celebration of royal nuptials and was titled My Old, that's O-L-D-E, Caribbean Wedding. Really? I did not know that. No, well, there's more history here. Stay tuned. Scandal ensued when the opening night performance was marred by a costume, quote, accident, unquote, that shocked the gathered throng. And these were all guys in those days, so, you know. Because of this debacle, Shakespeare renamed the play to distance it from its past.

For a few years, it was called Ariel, the Macho Pixie. This was deemed too pejorative. It was then turned into a musical using Gregorian chant and titled, you ready? I'm ready. Okay. Paint Your Flagon. Also, I did not know that. Gosh, I had no idea we'd get so much cultural history.

Yeah, Clint Eastwood sings in the musical, the film version of that, you know. Really? Yes. It wasn't until a successful revival in 1663 that featured children, puppets, and a bipolar monkey that it was renamed The Tempest. This from Christopher Regan, Regan or Reagan. And we thank you, but you didn't win. Sorry about that. Here's our winner.

Almost as fascinating, though not nearly as entertaining. Our winner. I'm sure he is if you met him here. I'm sure he is, and maybe he'll write back with a joke for us. Because our winner, the very first time we've had a winner from Iran. Hey, cool. His name is Mehdi, and I'll mispronounce it, but I think that's how to do his first name. Mehdi lives in Esfahan, Iran.

Mehdi, congratulations. We're going to get a Planetary Radio t-shirt out to you because you are right. Miranda was the moon, and the play was The Tempest. And there you go. On to the new contest. In your honor, Matt, we'll do a real-time contest switch. The question will now be the car. Subaru?

What does it mean? Subaru? There's a meaning? Oh, I just figured it out, because I know Subaru, and I'm not even going to say what I just figured out. No, I just know the company. There's a guy? Okay, I thought it was named after something else. If it was named after a guy, then just let us know.

How can people enter? I'd still go to planetary.org slash radio and follow the contest entry rules, because that's a great way to enter and win your T-shirt, no matter where you are from in our universe. Please get it in to us by Thursday noon Pacific time. We would really appreciate that. And you will, too, if your correct answer is the one chosen as next week's winner. And you'll get one of those Planetary Radio T-shirts.

Bruce, anything else? Yes, I just want to tell people to look up the night sky and think about all the names that the play Hamlet probably had. Thank you. Good night. Bruce Betts is the Director of Projects for the Planetary Society. He joins us each week for What's Up, Gadzooks. Back next week with more Planetary Radio. By the way, would you like to hear us on your local public radio station?

That's something we're working on. Drop us a line at planetaryradio at planetary.org. Thanks for listening.