October 29, 2019

subscribe to JPL Podcast



Episode 4: Deflecting Disaster

(movie: "These Final Hours")

"Is there anybody out there? It's happened."

[0:05] Narrator: Filmmakers and novelists love asteroids, especially if they're heading for Earth.

(movie: "These Final Hours")

"Approximate location of impact, the north Atlantic. As I speak to you right now, it's making its way towards our fair nation."


[:20] Narrator: Large rocks from space hurtling toward us make such handy plot devices. The impending end of the world is the ultimate ticking clock, creating an opportunity for dramas to escalate and heroes to rise. The possible destruction of our little planet causes us to reassess our lives, and treasure what we once took for granted.

In movies like 2011's "Melancholia," where a small planet hits us, or the 2013 Australian film "These Final Hours," where an asteroid slams into the ocean and generates an oncoming tsunami, there is no hope, only despair. But fictional asteroid strikes also have been mined for dark comedy.

Seeking a Friend for the End of the World (radio announcement)

"The final mission to save mankind has failed. The 70-mile-wide asteroid known as 'Matilde' is set to collide with Earth in exactly three-weeks time, and we'll be bringing you a countdown to the end of days, along with all your classic rock favorites."

[1:15] Narrator: The 2012 movie, "Seeking a Friend for the End of the World," manages to smile in the face of an unstoppable asteroid. The TV show Futurama's 1999 episode, "A Big Piece of Garbage," has even more fun, with an asteroid made out of trash coming back to us after we'd tossed it out into space.

Futurama: "A Big Piece of Garbage"

"Can't we just shoot a missile at it?

"We've simulated that on a supercomputer, but the ball is just too damn gooey. A missile would go right through it."

"But suppose we sent a crew to plant an explosive precisely on the fault line between this mass of coffee grounds and this deposit of America Online floppy disks?"

"In theory, it could work!"

[1:55] Narrator: The most Hollywood option, of course, is for us to divert or blow up the asteroid at the last possible second. Those are the outcomes in the 1998 films "Armageddon" and "Deep Impact." A more modern idea for dealing with such threats was depicted in the 1968 "Star Trek" TV episode, "The Paradise Syndrome."

1968 Star Trek episode clip, "The Paradise Syndrome."

Mr. Spock: "If we are not able to gain entry and activate the deflector mechanism within the next fifty minutes, this entire planet will be destroyed."

Captain Kirk: "The key must be in these symbols. We've got to decipher them."

Mr. Spock: "I've already have to some extent, Captain. They are musical notes."

Captain Kirk: "You mean entry can be gained by playing certain notes..."

(fades to)

Captain Kirk: "More symbols. Can you read them?"

Mr. Spock: "I do have an excellent eye for musical notes Captain, they would seem to indicate that this series of relays, activated in their proper.."

Captain Kirk: "Spock, just press the right button."

(laser sound)

[2:47] Narrator: Laser rays created by an advanced civilization aside, how realistic are these rescue scenarios? Can we prevent an asteroid from hitting us, or like the dinosaurs, must we resign ourselves to a fate the universe set in motion?

(intro music)

[3:33] Narrator: Welcome to "On a Mission," a podcast of NASA's Jet Propulsion Laboratory. I'm Leslie Mullen, and this is Season 2, Episode 4: Deflecting Disaster.


In 1967, MIT Professor Paul Sandorff asked his engineering class: what if an asteroid was heading for us? What could we do about it? At the time, people hadn't thought much about this, outside of science fiction novels. The asteroid threat in this MIT study was Icarus, which swings through Earth's neighborhood every 10 to 30 years, but is not projected to hit us.

When Icarus was first discovered, it was predicted to fly within 4 million miles of us in 1968, and some writers suggested it could hit us. Despite the assurances of astronomers, doomsday predictions spread around the world.

For MIT's Project Icarus, they pretended the asteroid really was going to hit. To deal with it as quickly as possible, they came up with a plan to repurpose Saturn V rockets meant to take the Apollo astronauts to the Moon. Some of these rockets could send out satellites to observe and survey the oncoming asteroid, while others would deliver six 100-megaton nuclear warheads.

(explosive sound FX)

No such warhead existed. The biggest bomb in the US arsenal was 25 megatons, and the biggest ever detonated was a 50 megaton Soviet test bomb, dropped near the Arctic Circle in 1961. The blast from that bomb was 1500 times more powerful than the Hiroshima and Nagasaki bombs combined. The Soviets had originally designed their bomb to be twice as powerful - 100 megatons - but held back because they feared it would not only destroy the plane that dropped the bomb, but the radioactive fallout would spread too far from the test site.

That wouldn't be a concern for an asteroid, though. Even though the MIT students didn't know much about the composition of Icarus, they thought 100 megaton nuclear blasts would just crater the asteroid's surface rather than smash it into smithereens. But the force of those blows should be enough to turn it away from Earth.

The 1979 movie, Meteor!, starring Sean Connery and Natalie Wood, was inspired by Icarus and the MIT Project.

Excerpt from 1979 movie, Meteor!

Dr. Alexei Dubov and Tatiana Donskaya: "He doesn't mean to criticize, but you will not find it easy to hit a meteor with your warheads pointing towards the USSR."

Dr. Paul Bradley: "We call ours Hercules, what do you call yours?

Dr. Alexei Dubov and Tatiana Donskaya: "How can one give a name to that which does not exist?

Dr. Paul Bradley: "Then who the hell put up this thing called "Peter the Great," its warheads pointing at the United States?

Dr. Alexei Dubov and Tatiana Donskaya: "Chinese, perhaps?"

Dr. Paul Bradley: (laugh) "Dr. Dubov, we've got a slight problem..."

[6:45] Narrator: Spoiler alert: in that movie, the US and USSR join forces to save the world. As the movie shows, the use of nuclear weapons is a heated political issue. In fact, there are several international treaties preventing the use of nuclear warheads in space. Here's Lindley Johnson, head of Planetary Defense for NASA.

Lindley Johnson: Well, Hollywood likes the dramatic stuff. They want big explosions, and there is no bigger one than a nuclear device. But when it comes to the real world, first of all, there are international treaties that prohibit not only exploding a nuclear device in space, but not even putting such a device into space. But if we were to get into a situation where a sizable asteroid was headed our direction and we didn't have a lot of time to do something about it, a nuclear device is the most explosive force that we have packed in a small enough package to get it out there in time.

And so we're working with an international group called the Space Mission Planning and Advisory Group, looking at what could we do to deflect an asteroid. And working within the auspices of the Committee on Peaceful Uses of Outer Space of the United Nations in discussing what would we have to do to be able to do a deflection mission. And one of the things that is being looked at by them is, what are the international treaty and legal aspects of electing to use a nuclear device if that was the last recourse that we had.

[8:18] Narrator: Some think using nukes in space is a bad idea, period. Due to the sensitive politics and security risks of nuclear weapons, by the time the nations of the world even agree to start putting together a mission against an oncoming asteroid, it might be too late. There are a multitude of issues to haggle over, from who pays for such a mission, to whether, by deflecting an asteroid from one country, you could accidentally send it crashing into another.

In the movie, "Meteor!," nuclear weapons are conveniently already in space: a Soviet satellite is pointing a bunch of warheads down at the U.S., and vice versa. Still, it takes the length of the movie for both sides to agree to turn them away from Earth, and fire them at the asteroid.

Excerpt from 1979 movie, Meteor!

Harry Sherwood: "General, I know this is difficult for you but I assure you..."

General Adlon: "Mr. Sherwood! Fifteen minutes ago, I spoke to the Secretary of Defense, who seems more aware of the complexity of the situation than you do."

Harry Sherwood: "But the Secretary..."

General Adlon: "His orders are, and I quote, there will be no change in the direction of our rockets until the Russians admit they've got their own rockets, and until they also agree to re-align them. Is that understood?"

Harry Sherwood: "Look. Why don't you Xerox 100 copies of that report, pass them out among 100 guys in Washington and then organize 100 meetings to discuss it, and by that time the meteor will have hit, and we won't have any more problems!"

[9:39] Narrator: According to Lindley, the movie's scenario of a space arsenal of nuclear warheads isn't realistic. Even the nuclear weapons we already have in silos on Earth probably couldn't be used in an asteroid emergency.

Lindley Johnson: Nuclear weapons aren't meant to survive long periods in space, and the radiation that they would be subjected to through a several-month to year-long cruise through space. So it would have to be a device that, in a lot of ways, was specially designed for this purpose.

[10:10] Narrator: One problem with blowing up an asteroid too close to Earth is that the shattered pieces could still rain down upon us and cause planet-wide devastation. The Icarus Project folks figured their super-powerful 100 megaton nuclear devices only had about a one-percent chance of shattering the asteroid, but if that did happen, they suggested using back-up bombs to pulverize the fragments. That wouldn't be so easy, though. Like in the 1980s Atari asteroid game, as the player shoots the asteroids, they break into smaller asteroids that are faster and harder to hit.

(Atari Asteroids game FX)

Rather than directly hitting an asteroid, a nuclear device could detonate near enough so the radiation bakes the asteroid's surface. This would, in theory, produce enough propulsive force to move the asteroid off course. But for some, nuclear weapons are a last resort, a "Hail Mary" of asteroid defense. With more time, there are other tactics we could try.


Some strategies seem very sci-fi, like turning the asteroid itself into a spaceship by strapping rocket engines onto it, and steering it away. But making that work is tricky.

Andy Rivkin: Asteroids have different rotation speeds, their north poles point in very different directions, so if you put a rocket on the surface, the rocket is going to rotate along with the asteroid. So you either need to only fire the rocket at certain times, when it's pointing the right way, or you have to figure out a way to change the spin of the asteroid so that the rocket can always work.

[11:52] Narrator: That's Andy Rivkin, a planetary astronomer at the Johns Hopkins Applied Physics Laboratory. He studies asteroids, and knows a lot about possible planetary defense tactics.

Andy Rivkin: Another one that people have mentioned for the future is having a really powerful laser and basically slowly melt away the asteroid. So in this case you could position the laser so that no matter what's going on beneath it, it's still going to be its own rocket in the direction you want. You're going to use the asteroid itself as fuel in a sense, and vaporize it away. So the challenge for that one is it takes a lot of power, and you'd probably need to have that power for a long time, so you need big solar panels.

[12:37] Narrator: For a low-power version of this space laser, some have suggested using giant mirrors or lenses to direct a focused beam of sunlight onto the asteroid.

Some deflection ideas are simple in principle, like using magnets to tug on metal-rich asteroids. Or installing a mass-driver to repeatedly drill out pieces of the asteroid and throw them into space, like a dog frantically digging a hole.

In the game "rock, paper, scissors," a winning strategy is "paper covers rock." Or in the case of asteroids, "reflective plastic covers rock." Sunlight bouncing off a plastic-wrapped asteroid could increase solar radiation pressure, giving it the gentlest of nudges. Another rock "cover" could be paint. If you paint it white, you increase the reflection of sunlight, just like with the plastic wrap. If you paint it black, the asteroid would absorb more sunlight and heat up. As the asteroid spins, its shadowed side cools, and this radiation of heat would (literally) provide a light push.

Another technique using sunlight would be a solar sail, which is propelled by charged particles flowing out from the Sun. If the asteroid's rotation wasn't a problem, then putting a solar sail on an asteroid could help it smoothly drift away on the cosmic sea.

These "soft and gentle" approaches don't seem like they could do much for a rock the size of a mountain hurtling towards us forty times faster than a rifle bullet. But the point is that, over a long time, the slightest touch can have a big influence. It's like compound interest on a cosmic scale; a galactic butterfly effect.

Ideas like these are fun to think about, but none have been tested in space. We have no idea if they'd actually work, or how well we could control the asteroid, or how hard it really would be to put such measures in place. You might even ask, how can we be sure anything we throw at an asteroid will make the slightest bit of difference?

(Asteroid Atari game sound FX again, 'game over' sound)

[14:45] Narrator: Our tools seem puny compared to the enormous scale of large asteroids. But Andy Rivkin says we can do it because of basic physics.

Andy Rivkin: The way the physics works is that if you have a particular position in space, relative to the Sun and the planets, and you have a particular speed and a particular direction, that completely defines your orbit. So, if you change that speed a little bit, you will change the orbit. And so that's often used to help calculate orbits for an asteroid, for instance, we'd say, "Okay this asteroid is in this place, it's moving this fast, that means now that we know its orbit." This is kind of that same idea, except we're going to give it an orbit we want by changing the speed. So the closer in time to an impact you try to do that, the greater the speed change you need to make. And the longer the period before the impact, you don't need to put as big a speed change in.

So this is kind of the opposite of trying to get away from a train. If you're on train tracks, then the way to avoid getting hit by the train is to step off the tracks, it's not to try to outrun the train. Here, the way the physics works, you want to change the speed of the asteroid, and then that will take care of moving it out of the way.

(train FX)

[16:06] Narrator: Scientists reviewing all the different ideas on how to change an asteroid's speed, and therefore its orbit around the Sun, came up with a "top three" list of preferred strategies. The strategies are: gravity tractor, kinetic impactor, and that old stand-by, nuclear devices.

A gravity tractor is the gentlest of the three approaches, and requires the most time: probably a few decades, depending on the asteroid's size.

Andy Rivkin: Gravity tractors use the mass of the spacecraft itself to gravitationally attract the asteroid, and then the fact that you can control one of them means that you basically put the asteroid in a different orbit, you give it the speed and the position you want it to have so that it can miss the Earth. But you need a really massive spacecraft, and it needs to operate very close to the asteroid in question.


[17:04] Narrator: The appeal of a gravity tractor is you don't have to worry so much about things like what the asteroid is made of, whether it's a solid body or a loosely-bound rubble pile, or how the asteroid is spinning. You also get very accurate tracking, so you can quickly see whether the asteroid deflection is working or not.

NASA was going to test the gravity tractor idea with the Asteroid Redirect Mission, also known as ARM. Here's Lindley Johnson again.

Lindley Johnson: This was a concept that was started back when we were talking about sending astronauts to an asteroid as some of our next steps in the human spaceflight program. But that would of course involve a mission of several months to years to send astronauts to even a Near Earth asteroid.

So the Asteroid Redirect Mission was a concept to send a robotic spacecraft to an asteroid, collect a piece off of it, I'm talking about a large piece, something several meters in size, you know, the size of a large room in your house. Collect that boulder off the surface of an asteroid, and bring it back to lunar orbit, where it then would be available to a human mission that would only be several days to weeks in duration.

But as part of that, we were talking about testing what we call the "gravity tractor technique," where you use Nature's tug rope - gravity - to slowly over the course of months to years change the orbit of the asteroid enough so that it no longer threatens an impact to the Earth.

[18:37] Narrator: The ARM mission got canceled in 2017, so the gravity tractor technique is still untested. The kinetic impactor technology did get a trial run 15 years ago, though. That's where you basically throw something heavy at an asteroid. Or in the case of the Deep Impact mission, you hit it with the equivalent of an 820-pound cannonball.

(Deep Impact movie trailer clip)

U.S. President: The United States and Russia have been building the largest spaceship ever constructed to stop the comet. We will prevail. Life will go on.

[19:13] Narrator: In the 1998 movie "Deep Impact," a manned mission was sent to deflect a large comet heading for Earth. A comet is basically an icy, dusty asteroid.

NASA's Deep Impact mission to comet Tempel 1 wasn't carrying nuclear warheads like in the movie, instead it had a copper-aluminum impactor. The point was to punch a hole into the comet's surface, causing material to explode outward so we could see what it's made of.

That impactor hit the comet at 23,000 miles per hour, smashing with the equivalent of 5 tons of TNT. The spacecraft that had released the impactor, and was watching from a safe distance, sent us photos of the bright flash of the impact explosion.

(NASA Deep Impact mission press conference)

Rick Grammier, Deep Impact Project Manager: Right now, we're minus one spacecraft: the impactor. (laugh) It's been totally vaporized, per plan. And we were right on target, as you've heard, and we have a healthy flyby spacecraft. It came together quite well, just phenomenal. It went very much like clockwork. We didn't exercise a single contingency plan in, and doing the trajectory correction maneuvers of it, you can see it all the way up to the end. We....(shouts and applause)


[20:34] Narrator: The metal impactor not only made a crater on the surface, it also nudged the comet the tiniest little bit. Calculations suggest the comet's speed changed by 0.0001 millimeters per second. To get a sense of just how microscopically small that is, one of your red blood cells is 80 times larger than .0001 millimeters.

But remember what I said about how a tiny nudge, given enough time, can lead to big changes in an asteroid's orbit? Well, at least for comet Tempel 1, scientists say this particular nudge doesn't matter. That's because the comet occasionally swings by the giant planet Jupiter, and when it does, it gets tugged by Jupiter's immense gravity so hard, that swamps any shift we made in hitting it.

But that brings up another issue with testing any asteroid deflection method. There's a fear that by interfering with asteroids, we could inadvertently send them on a path to Earth.

That won't be an issue for NASA's upcoming DART mission, which will be the first true test of the kinetic impact method. DART is an acronym for Double Asteroid Redirect Technique. Andy Rivkin is the co-lead of the DART investigation team, along with Andy Cheng, another scientist at the Applied Physics Lab who came up with the idea for the mission.

Andy Rivkin: So the kinetic impactor is simple: you come in, you whack it, and then if you need to do it again, you come in and you whack it again. So I think it was about 2011 that Andy Cheng realized that you could do this with a binary asteroid system, so an asteroid with a moon. And binary asteroids are probably about 10 to 15 percent of the near-Earth object population, so they're pretty common. But to have them easily accessible by spacecraft in the time frame that we want, and also observable from the ground... Each time you add another thing you want, there are fewer and fewer that work.

So Didymos is a great target, and it's really the only one we have for the next, I forget if it's 20 years or 30 years, or maybe even more. So Didymos is certainly the best choice we know of, it might be the only real choice out there.

So for DART, we're going to impact the moon of the Didymos System, Didymos B. There is no chance we are going to have this hit the Earth. This is not anywhere near an Earth-crossing orbit. We are impacting the moon, so we're not impacting the main body. Technically speaking, if you go and do enough zeros and did long division long enough, we will change its orbit around the Sun, but we are going to hit it from a direction so that it moves further from the Earth, and we are also hitting the moon in the direction so that it moves closer to the primary. We're not going to accidentally knock it out of orbit or anything crazy like that.

[23:33] Narrator: "Didymos" is the Greek word for "twins," but this asteroid pair don't look identical. Didymos B is five times smaller than the 800-meter diameter Didymos A. Some people have nicknamed the smaller of the two asteroids the "Diddy-moon."

(P. Diddy remix: Been around the world, chorus)

[24:04] Narrator: When the DART mission smashes into the Diddymoon, that impact should slightly change its orbit around Didymos A.

Andy Rivkin: So we know it's something like 11.92 hours that the moon goes around. Once we hit it, that will change, it will no longer be 11.92 hours, we don't know what the new number will be, we expect it will be more like something like 11.8 hours, it might even be much shorter.

We're going to measure what we did using telescopes on the ground, so it's an unusual mission in that, things really start when the spacecraft is gone. So the observations on the ground are going to be done by telescopes all over the world.


So from the Earth, from even the most powerful telescopes, Didymos A and Didymos B will just look like one point of light. So we watch the brightness go up and down with time, both as Didymos A rotates and as Didymos B goes around it in its orbit. And in particular, there are times when Didymos B will move in front of Didymos A and block some of its light, and move behind it and be blocked. So these are basically little eclipses.

So we don't think we'll be able to see the impact flash per se. We imagine we are going to kick up a lot of debris, and that debris will reflect its own light, so we think it's possible that the system will brighten, we think it's possible the system will grow a tail and a coma. There are other asteroids that we think have been impacted in the asteroid belt, of course we don't know for sure, but we see them with a tail and kind of we back out, "Okay this must have been what happened." And we see the tail evolve and lengthen and then eventually go away. So, we're certainly not promising anything, I think it would be great if we did generate something like that, then people could go to their local planetariums and go at the public viewing night and see, but we're not sure if we're going to do that.

[26:04] Narrator: We're not going to just rely on telescopes on Earth to view the event, though. The spacecraft will have a camera to send us pictures, up until it sacrifices itself to the Diddymoon. For a close view of the spacecraft's impact, flying along with the DART mission will be a CubeSat - a small satellite the size of a cereal box. /

Andy Rivkin: The plan for the CubeSat is that it will detach a few hours before the impact, and it will slow down, so that DART impacts before the CubeSat gets there. And then the plan is to have it take pictures of the impact to see if it can see the debris that the impact kicks up. We think that from the amount of debris and the shape of the debris cloud, we can determine things about the surface of Didymos B. That will be information we can't get any other way. And then, we are hoping that the debris will clear fast enough that the CubeSat can get a picture of the crater -- we don't necessarily expect that to happen, but you know, fingers crossed.

[27:07] Narrator: The DART mission plans to launch in two years, and smack into the Diddymoon in the Fall of 2022. Observers on Earth will be able to watch the binary asteroid up to about two months after impact.


Andy Rivkin: Every two years or so, Didymos gets to be bright enough that our telescopes can see it easily and its far enough from the Sun that we can see it at night. For the period when we impact, it's coming close enough to the Earth that the window of time we can observe it is longer. So we can start to observe it in the late spring of 2022, and then we impact in the Fall, and then it's visible through early 2023 and then it gets too close to the Sun, and we're done until late 2024, and then we can observe it again and again in 2026, et cetera. So, certainly we'll be interested to see how it looks in 2024 and to see if anything has changed since the last time we had observed it.

And then our European colleagues are working on a mission called Hera, which they hope to fly not long after us, and I think that would arrive at Didymos in 2026 and do some close-up measurements, actually see what the crater looks like, see how we changed the surface, see if anything hit the main body, et cetera. We think that that would be a great addition, and really complete the picture of the Didymos system.

[28:34] Narrator: For all the studies of asteroids and the various plans dreamed up on how to control them, they remain somewhat elusive.

Andy Rivkin: For asteroids, there's just so much we don't know. Every mission is a surprise, every time we get new data it's a surprise. I really do like the mystery of it.

From the science end, it's really a rush when you get some results back and you say, "Wow this doesn't make any sense, this is great, let's get together and let's figure out what could this mean?" And that's the best feeling. And for planetary defense, on the other hand, there's definitely a sense of, "Look, we want to know, we don't want to show up and have it be a surprise. We want to test this thing out and know it's going to work."

The planetary defense angle has been newer for all of us. The first real recognition that this could be important was the realization that an impact probably caused the extinction of the dinosaurs. That was the first real eye-opener for some folks. I mean, I remember - well, I guess when I was in grade school, we didn't know what killed the dinosaurs, and there were a lot of theories. There's a Far Side cartoon -- I don't know if people even know the Far Side anymore, but it was a popular cartoon in the newspapers -- and it had a set of dinosaurs all smoking, and it said, "The real cause of what killed the dinosaurs." Because it was as good an answer as any at the time.

So it has really come a long way, and something like DART 20 years ago would have been deemed kind of outlandish. And now, these missions and the like are seen as more of an insurance policy. And they don't cost a whole lot, certainly compared to other things that we similarly see as insurance policies. And so developing the capability, understanding what's out there, only seems prudent.

I think having a steady string of planetary defense missions would be great. I could imagine, depending on the outcome of DART, maybe we would say, "Okay, next time, instead of hitting another binary, we'll hit a single target and see if there's any difference there." Didymos has a composition that's the same as the most common meteorites, so it's the obvious thing to start with, but there are other compositions. And I could imagine ultimately saying, "Okay, what if we had an iron asteroid that was coming in, do irons act differently?" And you could imagine missions landing on asteroids, and you would get information that would be useful to both the science and the planetary defense communities.

[31:09] Narrator: Next time, On a Mission.

Excerpt from Episode 5: Catch a Falling Star

Bill Bottke: So right now we're visiting the asteroid, Bennu. Bennu has turned out to be this amazingly fascinating world. And I've also been enjoying watching the mission Hayabusa2 from the Japanese space agency. They're going to this asteroid, that's a little bit Bennu-ish called Ryugu. And we're both going to bring back samples. The story they tell is going to be about planet formation, but also what's happened in the asteroid belt over the last few billion years.

[31:36] Narrator: If you like this podcast, please subscribe, rate us on your favorite podcast platform, and share us on social media. We're "On a Mission," a podcast of NASA's Jet Propulsion Laboratory.

[run time 31:46]