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Are asteroids dangerous? Just ask the dinosaurs, and they’ll tell you a sad story of fiery death. It turns out we’re in a shooting gallery of space rock and metal, and somewhere out there there’s one with our name on it. Should we be worried or are the risks so minimal to be irrelevant?
Download MP3 | Show Notes | Transcript
NEO Basics (NASA JPL)
Potential Energy (Ducksters)
Tsunamis (National Geographic)
Larry Niven’s Lucifer’s Hammer
A meteorite crashes through a home in Canada, barely missing a woman’s head (NPR)
Peekskill Meteorite (AMNH)
Today in science: The Chelyabinsk meteor (EarthSky)
1908 SIBERIA EXPLOSION: Reconstructing an Asteroid Impact from Eyewitness Accounts (PSI)
Chondrite Meteorite (AMNH)
Antarctic Study Shows How Much Space Dust Hits Earth Every Year (Scientific American)
Researchers Have Taught a Drone to Recognize and Hunt Down Meteorites Autonomously (Universe Today)
ANSMET, The Antarctic Search for Meteorites (Case Western Reserve University)
Jet Propulsion Laboratory (NASA)
CNEOS (NASA JPL)
NASA Analysis: Earth Is Safe From Asteroid Apophis for 100-Plus Years (NASA)
NEO Surveyor (University of Arizona)
Planetary Defense (NASA)
Chicxalub Impact Site (LPI)
Double Asteroid Redirection Test (JHUAPL)
Ten Things to Know About Bennu (NASA)
The Dark Asteroid Ryugu Finally Comes Into the Light (Wired)
Background On Bennu Mappers: Rocks All The Way Down (CosmoQuest)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast, Episode 623, “Near-Earth Objects: Concern or Nah?” Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know. I’m Fraser Cain, Publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey, Pamela. How are you doing?
Dr. Gay: I’m doing well. It’s that time of year where it feels like everyone is either sick or distracted by the holidays and –
Dr. Gay: – and just living for the weekend. And here we are recording Friday afternoon and I know I am, for one, living for the weekend.
Fraser: Literally the second this show stops I’m gonna play some videogames. My newsletter is out the door. My work is done for the day. All my writers are working. Everything’s going great. I’m gonna drop everything, eat some noodles and play some videogames. That’s the plan.
Dr. Gay: Minecraft 1.18 is out. I’m hoping to get to take a look at that this weekend.
Fraser: Awesome. I played with Chloe last week. We played some Minecraft a bit.
Dr. Gay: Awesome.
Fraser: People keep asking me if I have the cape from taking Chloe and Logan to Minecon, the first one. And so, people keeping wanting to buy my account. You can’t have it. It’s mine –craft. All right. Let’s get on with this week’s episode. Are asteroids dangerous? Well, just ask the dinosaurs and they’ll tell you a sad story of fiery death. It turns out we’re a shooting gallery of space, rock, and metal, and somewhere out there there’s one with our name on it. Should we be worried, or are the risks so minimal to be relevant? All right, let’s first start with the horrible worst-case scenario. How bad can asteroid impacts be?
Dr. Gay: A really bad one will turn the surface of the planet completely molten, toss the crust off of our world, and create a new moon.
Fraser: Oh. Right. Okay. All right. Okay.
Dr. Gay: I think I went a little further than you were looking for there.
Fraser: But that’s like if Ceres crashes into the earth. So, of the types of space objects that are in our area, in a near-earth object region –
Dr. Gay: Right.
Fraser: – what is a bad day for humanity?
Dr. Gay: A bad day for humanity is when you have something come through and hit, worst case, in some ways is solid ground because then it throws all the debris up and all the kinetic energy it gains from the shockwave of the impact gets turned into heat energy as it comes back downwards; also, the gravitational potential energy. And all of that heat getting added into the atmosphere kinda turns our planet into an oven, which isn’t what we want. Now, on the other side, though, of trying to define “bad day for humanity,” if you hit the ocean just right you generate giant tsunamis that essentially inundate everything. Where folks at the top of mountains are good –
Fraser: Well, apart from the atmosphere, everything being like an oven, that still happens anywhere you –?
Dr. Gay: It’s still gonna happen; it’s just a different format and different amounts of energy. At least with the tsunami, some of the energy’s getting redirected into water. Not enough, as the dinosaurs learned. Not enough.
Fraser: Including the ones that went to orbit?
Dr. Gay: Yes.
Dr. Gay: Well, they didn’t die from the heat of the atmosphere getting baking hot. They died from the fictional heating of the atmosphere.
Fraser: They fortunately were able to avoid it, but you get this impact event. All of this debris is thrown up into space. It then re-enters the earth’s atmosphere, heats up, drops molten rock around the planet, lights the world’s forests on fire. It can be bad, very bad. All right.
Dr. Gay: And there’s some amazing science fiction that really gets this right. Larry Niven’s Lucifer’s Hammer and Neal Stephenson’s Seveneves both really describe bad ways to wreck the world.
Fraser: Absolutely. Lucifer’s Hammer, that was a terrifying book. I read it and I was pretty young. I think I was like in my late teens when I read that book, and that definitely freaked me out as a way to go.
Dr. Gay: I read it while attending a science fiction convention where I knew I was going to get to meet Larry Niven, and it’s just sort of like, of all the things I could have just put in my brain, this was not the right one.
Fraser: Right, right.
Dr. Gay: Excellent book, though. You will stay awake.
Fraser: Not The Mote in God’s Eye, but instead Lucifer’s Hammer. All right, so now we know that if a asteroid hits the earth, it’s a very bad for humanity and then to all life on earth. What are the chances that a large asteroid is going to strike the earth in the future ever, in the near or far future?
Dr. Gay: Ever, ever, it’s 100%.
Fraser: 100%. 100%. So, we got 100% chance.
Dr. Gay: In the ever.
Fraser: In the ever. 100% chance of a large asteroid striking the earth and causing the kind of destruction, dinosaur-orbiting destruction that we mentioned earlier. Okay, all right. So, now we got one side of the spectrum. So, now temper this conversation. What are the chances of it happening on any given year?
Dr. Gay: Negligible. And this is where statistics gets super funky because when you say the earth gets struck by this kind of thing every 200 million years or so and it’s been 200 million years pretty much since the last really bad impact, that isn’t to say that this is going to occur every 200 million years. This is saying that over the fullness of time when you take this completely randomized process and average it over the fullness of time, it occurs roughly every 200 billion years.
Dr. Gay: But the reality is you could get two years in a row that are really bad for our planet.
Fraser: That would be super unlucky.
Dr. Gay: Really bad. And then, you can also go a billion years and be fine. Probably not gonna happen. There’s probably gonna be something out there that gives us a bad day –
Dr. Gay: – but it’s any given year you’re looking at that one in 200 million-ish issue.
Fraser: But it’s not like there are only large asteroids out there. There’s a distribution curve of smaller and smaller asteroids and the smaller ones hit more often. So, how likely are we to face some kind of asteroid impact at some point that causes some kind of damage? I know that was a lot of weasel words but –
Dr. Gay: Right, so I wanna say that just last week someone heard a really loud noise and went to explore, and it turned out the meteorite had crashed through their roof. These things happen on the years-to-decade kind of level where a car gets hit, a rough gets hit. And –
Dr. Gay: – the more stuff we build, the more things are going to get hit.
Fraser: All the cities in a Russian town get exploded?
Dr. Gay: All the buildings in a Russian town, yeah. All the windows.
Fraser: All the windows in a Russian town get exploded. Trees in a vast chunk of Siberian Forest get knocked over, a hole is gouged out of the Arizona desert.
Dr. Gay: Well, that one was kind of extreme. But someone getting a hole in their ceiling from a space rock isn’t that much damage compared to a lot of the stuff that we get just from a massive storm putting ice on all of the trees causing the limbs to fall off and shatter rooves left and right. So, I’ll take a space rock over an ice storm any decade.
Fraser: Right, unless it hits your roof.
Dr. Gay: Still would cause less damage than the trees out there.
Fraser: Okay fine. All right. We’ll talk more about this in a second, but it’s time for a break.
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Fraser: So, okay, fine. You’re talking about small rocks going through people’s roofs and landing gently on the pillows besides them. Let’s say, what is the minimum size where we’re starting to see some real damage to people who happen to be unfortunately under an asteroid strike?
Dr. Gay: This is a double-sided problem. There is, first of all, what is the composition of that rock coming down? Because if you have a metal-rich asteroid, meteoroid coming through the atmosphere it’s gonna survive the atmosphere a lot easier. So, you’re looking at something that is measured in meters, is gonna make it to the ground and make a divot in someone’s back pasture. If, on the other hand, you have something that is a really carbon-rich chondrite piece of mineral rock coming down through the atmosphere, it could be the exact same size and burn itself up completely through frictional heating.
So, you’re looking at not just how big is it, but what is that sucker made out of. And so, when you get a many meter-across chondrite, you can end up with bowling ball-sized chunks spread over – well, there was a really cool one back in 1969 that came in exploded over the Chihuahuan Desert and left tons upon tons of debris for folks to come pick up and do research on. And so, if you want that giant single divot in your yard, you need a big old metal meteorite. If you –
Dr. Gay: – want scattered, less dangerous stuff, if you ignore the sound wave – that was what got everybody in Chelyabinsk – you want a carbonaceous chondrite.
Fraser: There’s actually people who go with metal detectors to farmers’ fields looking for those metal meteorites and they find them. It’s kind of amazing.
Dr. Gay: We have hundreds and hundreds and hundreds and hundreds of tons of debris hitting our world every year, and most of it goes unnoticed. Most of our planet is water and we’re just not seeing it come in. A lot of the planet is agricultural. We don’t notice it coming in. And we’re starting to really get a sense of how bad it is. There’s a project in Australia where they have people setting up digital cameras, single-lens cameras, all over Australia pointed at the sky and they’re catching the streaks coming in and then going into the Outback to collect the rocks. And this is a regular occurrence, and now we know just how regular it is and they’re getting way better at collecting all those rocks.
Fraser: We did a story on Universe Today about this; that they built a drone with some machine learning algorithm on it that can recognize meteorites and collect them autonomously. And so, they just send this drone out. It flies across the landscape, looks for potential meteorites, picks them up, brings them back to the researchers, and they can confirm whether or not they’re actually meteorites. And, of course, we know that people do this out in Antarctica as well. Because you find a rock sitting on top of the snow on a kilometer of ice in Antarctica, it probably came from space. So, we know this stuff is falling all the time. To a certain size, they start to cause some kind of damage.
So, if we blend all of these ideas together, how much of a threat are we from some kind of near-earth asteroid in our lifetimes?
Dr. Gay: So, the Jet Propulsion Lab keeps track of all known objects that have earth-crossing asteroids and their Sentry Program ranks them by just how dangerous they are. And right now, there is nothing that is hazardous that is slated to hit our planet. And there is two major survey programs out there. NEOWISE’s looking for stuff that we would have time to deflect and ATLAS’ looking for stuff that we missed until it was too late.
Dr. Gay: And those two programs are making massive inroads into both finding out just how much stuff do we not notice until it’s too late, ATLAS, and just what is out there waiting to be discovered will hit us. And so far, Apophis got really interesting a couple decades back, but with follow-up study we keep finding we’re safe right now. We’re safe.
Fraser: But are we? I think we know at this point NASA has tracked the 1-kilometer asteroids and know that none of them are at any risk to us, but we continuously discover, thanks to ATLAS, for example, meteorites that would have been hazardous and we didn’t know about them as they fly past the earth. So, in theory, there are some asteroids out there that can impact us and cause damage and it’s completely random. I forget what your chances are. You’re like one in some vast number; like one in hundreds of thousands to die from a meteorite strike in your life.
Dr. Gay: You’re more likely, if you’re a normal person who goes on vacations, to die in an airplane crash.
Dr. Gay: And this is where completeness becomes an issue. Space is big, finding small, rocky things is hard, and it gets even harder when they’re dark. And a lot of these objects are really dark and they just don’t reflect that much sunlight back to us. And so, the concern is we’re probably at the 90-some-odd percent of the big stuff that could destroy us as a society has been discovered. And it’s the stuff we haven’t found that keeps people awake at night and leads to funding of things like the Large Synoptic Survey Telescope, which is now at Vera Rubin Observatory. It’s the medium, city-sized stuff where we know we’re not nearly that complete that gets projects –
Dr. Gay: – like NEOWISE funded.
Fraser: Well, we’ll talk about that in a second, but it’s time for another break.
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Fraser: And we’re back. So, we talked about knowing some percentage of some of the asteroids of some sizes, and you started to hint at some of the plans. So, the goal now is to find the objects and try to get a much better sense of how much risk we face because it’s still kind of an unknown. So, what are some of the projects that are attempting to figure out what kind of a cosmic shooting gallery we actually live in?
Dr. Gay: So, right now the big folks out there finding stuff, and you know their names from all the comets that they’re finding along the way, are: NEOWISE, which is mapping out pretty much anything it can find that is far enough away that they can get good orbit. And NEOWISE is turning up asteroid after asteroid, comet after comet, and filling in the known objects in the earth orbit. Now, near-earth orbit means things that are orbiting the sun in an orbit that is near earth’s orbit. It doesn’t necessarily mean it is near the planet earth. ATLAS is out there looking for the stuff that isn’t just near-earth asteroids but objects that are really close to our planet sometimes getting ready to dive through the atmosphere.
ATLAS has found a few of those where it alerts folks to “Hey, this thing is coming. Take pictures.” So far, no one has had to take refuge. But ATLAS will warn us of the things we don’t have time to deflect, and NEOWISE will warn us of the things that we’re, well, working to test technology to allow us to deflect.
Fraser: And we’ll talk about technology to deflect in second. And this is not time for another break. But there are some other missions in the works, even some space telescopes in the works to try and detect the vast number of asteroids that are out there.
Dr. Gay: And here, so many things. And I have to admit, as always, I don’t necessarily pay that much attention until things are off the planet –
Fraser: Because it doesn’t exist?
Dr. Gay: – and fully functioning. I’m good with keeping track of the stuff being built on the surface of the planet because I’m pretty sure they can get that stuff working. So, the next big survey is gonna be the Large Synoptic Survey Telescope, which is going to be finding all the tiny stuff night after night that is moving at a reasonable cadence across the sky.
Fraser: NEO Surveyor, the one by Amy Mainzer –
Dr. Gay: Oh, yeah.
Fraser: – is essentially the successor to NEOWISE. It’s gonna be an infrared based observatory but really focusing on planetary defense. Its one job is gonna be to search for asteroids in our vicinity. And as you say, they’re dark, and so generally the best way to find them is in the infrared spectrum because they do give off a little bit of warmth. And so, you can find them with infrared. And so, the NEO Surveyor is actually a relatively inexpensive space craft. It’s expected to launch in 2026 and should find like all of them. It should be able to find most of these scary asteroids at that point; the ones that are bigger than 140 meters.
Dr. Gay: When we talk about asteroids, we generally are like, “Zero to 30 meters, that could be a bad divot but not a city killer. 30 to 100 meters, here you’re starting to talk about bad day for a small township. 100 to 300 meters, city killer. Beware.” It’s when you get over a kilometer that the dinosaurs start saying, “Now, it’s your turn.”
Fraser: Well, the one that killed the dinosaurs 65 million years ago, that was 10 kilometers across. The Chicxulub meteorite. But a 1-kilometer asteroid would render a hemisphere unhappy.
Dr. Gay: And again, it’s gonna depend on where it hits just how unhappy everything is. It’s crazy.
Fraser: Hyperbole when I use the word “unhappy”. What I mean is, for some large area everybody dies. And then, for areas around that there’s more and more damage and fire and debris and property destruction and so on and so forth.
Dr. Gay: I like the Firefly definition of “interesting” which is “Oh my god, we’re all going to die.” Right.
Fraser: Well, we know the universe is trying to kill us, so this is one of the many tricks it has up its sleeve. Now, we’ve talked a lot about all the crazy, theoretical ideas that could be possible to try to deal with an incoming asteroid, right? And again, we could do a two-part episode. I think we have done a two-part episode on all the ways to protect ourselves from asteroid impacts. But finally, NASA is doing something actually proactive about an asteroid and has launched a mission.
Dr. Gay: It has. This is DART. It’s carrying along with it two little cube sats, LUKE and LEIA. Those are backronyms of adorableness. And it only has one camera on it, but when your job is to strike a asteroid’s moon one camera’s all you need. And that camera is modeled after the LORRI camera on New Horizons, so we know it’s a good one. DART is on its way out to an asteroid that is in no way in danger of striking the planet earth. We are fine. Its orbit –
Dr. Gay: – isn’t that much bigger than ours but it doesn’t overlap ours. We’re safe.
Fraser: But it is a near-earth object. It’s the kind of object that we should be worried about; just we’re not worried about this one.
Dr. Gay: It’s not an earth-crossing asteroid. And what they’re going to do is, when they get really close to the asteroid Didymos that has a moon called, officially, Dimorphos and unofficially “Didymoon,” which a way cooler name.
Fraser: It’s the best.
Dr. Gay: So, when it gets close enough, it’s gonna launch those cube sats and it’s gonna fling itself into “Didymoon”. And the reason that they’re going into the moon is they can see the moon’s orbit around the larger asteroid and measure the timing of it really accurately. And since they know the mass of the DART space craft and they know the original orbit of “Didymoon” they can look at how much the orbit changes, which could be up to 10 minutes, which is not that exciting but easily measured. Since that change in orbit could be up to 10 minutes, they can actually see how much of the kinetic energy of the space craft is imparted to the moon. And the answer could be anything from it’s like Bennu and they just kind of end up embedded inside a ball pit –
Dr. Gay: – of a moon –
Fraser: I love that idea, that thought. Just “foomp”.
Dr. Gay: These are the things that keep me up at night.
Fraser: For sure. It just goes “foomp” and just disappears into a fluffy pile of rock.
Dr. Gay: And the asteroid gets floofed out instead of, really, deflected. But at the same time, this could be a really sold fragment that got knocked of Didymos at some point in the past and is just like a boulder in space. And you hit a boulder that’s a solid and you get really good in elastic collisions that can cause your splat of a space craft, to do a good job.
Fraser: And when is the impact set for? When’s that gonna happen?
Dr. Gay: It arrives in September of next year and I don’t know if there’s any plans to be able to change the counter date at all, but we’re definitely looking at September –
Dr. Gay: – of next year.
Fraser: Fantastic. All right. So, now we know there’s work being done to find and categorize the dangerous objects, and now NASA is actually sending a mission out to tap on one of these asteroids to see what happens. So, I feel like this existential risk is now firmly in hand and people are trying to figure out solutions. Kind of exciting. Not so scary anymore.
Dr. Gay: It’s super exciting. Well, and Ryugu and Bennu taught us to be afraid of rubble-piles. They really, really did.
Fraser: Only if you’re trying to count the rocks on them, but sure.
Dr. Gay: I may be scarred.
Fraser: I think you are. I think you’re a little scarred from that. Well, thanks, Pamela.
Dr. Gay: My pleasure, Fraser.
Fraser: Do you have some names for us this week?
Dr. Gay: All right. So, as always, we are funded by our amazing community over at Patreon and this time last week, we had 666 patrons –
Fraser: That’s the number of the beast.
Dr. Gay: – which is a number. But we have like 30,000 of you out there listening. And so, I like palindromes. Yesterday was a beautiful date. It was 2021/12/02 and you could read it both directions. You could flip it upside down. It was perfection. My goal is to see this show eventually get to 888 patrons –
Dr. Gay: – which is my goal. If you like palindromes and you wish for a better one than 666, please become a patron and we’ll send you extra content.
Fraser: I don’t know, Pamela. 666 is a cool number. That’s gonna not convince a lot of people. But anyway, give it a try. We’ll reach like 777 or 888. Let’s hear some names.
Dr. Gay: This week we want to thank Gabriel Gauffin, Kseniya Panfilenko, Neuterdude, Benjamin Davies, Sean Freeman and Blixa the cat, The Mysterious Mark, The Air Major, Joe Wilkinson, Claudia Mastroianni, Bart Flaherty, Brian Kilby, Dean, Lew Zealand, Corinne Dmitruk, Tim Gerrish, Aron Tannenbaum, Naila, BenFloss, Arcticfox, Robert Wenger, Jordan Turner, Rayvening, Allen M. Price, Mark Van Kooy, chris wheelwright, Jason Kardokus , Olivia Bryanne Zank, Ron Thorrsen, PAPA1062, Robert Hundl, Kim Barron, Vitaly, Leigh Harborne, Mark Phillips, Kathleen Mattson, Bob the cat, Saebre Lark, Dwight Illk, Peter, Benjamin Müller, Micheal Regan, Brent Kreinop, Paul Esposito, john öiseth, Ruben McCarthy, Uhmu, Geoff MacDonald, Wayne Johnson, and Iggy Hammick.
And you can change your name to a pronunciation guide if you want me to say it right.
Fraser: That’s a good idea. All right, thank you everybody. Thanks, Pamela.
Dr. Gay: Thank you. Bye-bye. Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons attribution license. So, love it, share it, and remix it but please credit it to our hosts, Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website astronomycast.com. This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep the show going, please consider joining our community at patreon.com/astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.