New asteroids are found every day, and every day we learn that those asteroids don’t have any murderous intentions. But how do we learn that? In this episode we dig into asteroid orbital determination.
Show Notes
- Detection of Near-Earth Asteroids (NEAs)
- Discovery Methods
- Recent Discoveries
- Orbit Determination and Risk Assessment
- Calculating Trajectories
- Impact Probability
- Mitigation Strategies:
- Planetary Defense Initiatives
- Future Missions
- Public Communication and Perception:
- Media Sensationalism
- Educational Outreach
Transcript
AstroCast-20250224
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Fraser Cain: Astronomy Cast Episode 745 How Do We Know When Asteroid Will Attack? Welcome to Astronomy Cast, our 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. I’m the 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. Pamela Gay: I am doing well. I am currently dealing with some allergy situations, so if you hear me coughing, I’m not sick. I just have stupid allergies, but yeah, I have never been more grateful to all of you on Patreon.
As we watch everything going on, I’ve had all of my colleagues struggle with funding and stuff. So Patreon people, you allow me to wake up a little bit less scared of my inbox. So thank you.
Fraser Cain: Yeah, I have the same – like, I have a different – as a Canadian facing down tariffs from the United States and all the disruption that’s going to be happening, I have the same ability to breathe easy thanks to everybody who has already become patrons. It’s kind of amazing at this point how stable I’m able to make Universe Today and like a lot of writers are coming out of the woodwork and saying, hey, Fraser, do you have any more work? Stuff’s drying up.
And I think that is now going to accelerate and I want to save them all, but I can’t. So yeah, so for those of you who have already become patrons of either Astronomy Cast or Universe Today or CosmoQuest or all three, thank you so much. For those of you who are on the fence and kind of going like, oh, is this it?
Is this the time? Is this when I directly support the creative work of the podcast and the media that I really enjoy? Yes.
Dr. Pamela Gay: Yes.
Fraser Cain: This is the time. This is the moment. This is the moment you’ve, you know, we’ve all admired your stoicism from afar, but now you need to jump in and you need to help the, and not just us, I mean, we are, we’ve already been supported in the large part by, by, by patrons and sponsors, you know, we’ve been very good, but there’s a lot of channels out there.
I think about all the stuff that’s run by PBS, the stuff that’s, you know, a lot of educational content that has some level of financing through, you know, various government grants and things like that, they’re going to get massacred shortly. So think very carefully about how you consume content, which channels you are most grateful for and then figure out how you can support those creators directly with, you know, if you, if you watch a thing and you love it, support it directly because if, if people don’t do that, then that thing will just disappear and it will be replaced with AI slop. It’ll be replaced by a substandard version of it.
And this is the spiral that we are now approaching. And so I think, you know, for both of us, I think we’re going to be able to weather this. A lot of places out there aren’t going to be able to weather this.
And so just now is the time, contribute directly to the content that you find wonderful. All right, I’m sure you’ve heard the news. Asteroid 2024 YR4 has a tiny chance of hitting Earth in 2032.
How do astronomers discover these dangerous asteroids, measure their future impact risk, and track the changes over time? When should we panic?
Fraser Cain: We’ll talk about it in a second, but it’s time for a break. And we’re back.
Fraser Cain: All right, Pamela. So before we talk about just like how this all works in general, you know, we are in the late February 2025 and we can give you sort of a status today of YR4 and then we will begin to dismantle the whole proposition and move forward. So where do we stand today with YR4?
Dr. Pamela Gay: So as of 1.16 p.m. on February 20th, that is in central time and these numbers are changing as data gets reduced and understood.Hourly.
Dr. Pamela Gay: Yeah, exactly. We are sitting at a 1.5% chance of the Earth getting impacted and a 0.8% chance of the moon getting impacted in 2032.
Fraser Cain: Right. December 2032. And what we know about the asteroid, it is probably about 50 meters across, could be as big as 80 to 100 meters across.
Like if you, the most accurate number crunching right now tells us that it’s going to come within about 160,000 kilometers of Earth, which is close. Like that is…
Dr. Pamela Gay: It’s closer than the moon, further than the geosynchronous.
Fraser Cain: Yeah, yeah. Geosynchronous is say 35,000 kilometers. The moon is, you know, on average 400,000 kilometers or 384.
So it is half, less than half the distance from the Earth to the moon. Now you mentioned, it’s funny because so you mentioned 1.6% chance of it hitting Earth. And like yesterday that we’re recording this, it was 3.1, yeah, it had already gone to 3.1. And then today we got this, this lowering of the odds down to, to 1.6. 1.5. It’s actually 1.5 now. 1.5 now. Okay. Like since we started recording this episode.
Dr. Pamela Gay: Yeah. So I’m looking at the NASA century. Yeah.
Fraser Cain: Yeah. All right. So, so let’s first, so that’s, so that’s the situation.
And then let’s chat a bit about worst case scenario. Okay. Let’s say that a 50 to 100 meter asteroid did strike the Earth.
How bad would that be?
Dr. Pamela Gay: So to, to put the size of this into a perspective that, that is easier to understand than meters, this is the size of a 747, give or take. But because of the amount of energy it impacts, pun intended, as it blasts towards us with a really high kinetic energy, if this thing was a solid iron core, we’re looking at something like the Beringer crater, the crater that’s in Arizona, more likely this is something that’s going to go boom in the atmosphere. And we’re going to end up with a Tunguska like event that just flattens a region.
Now this is what’s called a city destroyer for small enough values of city. Uh, it’s bad, but it’s the kind of thing that since it will have a really good approach in 2028, that will allow us to get an extremely accurate orbit. We will either be able to say we are going to move that and move it.
Fraser Cain: Right. Well, we’re going to talk about that later on in the episode because that doesn’t, that’s not going to be as simple as we hope.
Dr. Pamela Gay: True. Yeah. Um, but it’s also the kind of thing where we could evacuate the necessary parts of the planet that would either be a land area or a whole lot of shoreline if it’s slated to hit the oceans.
Fraser Cain: Also part of the conversation that I want to have later. All right. Mitigation.
Yes. Yes. But, but, but the point being that you say city killer.
So if it does hit a city, that’s, it is like a 20 megaton nuclear weapon going off.
Dr. Pamela Gay: In the middle of a city and, and it’s either going to be an air blast that causes things to go flat. Yeah.
Fraser Cain: Which is not great. Not good.
Dr. Pamela Gay: No, no, no. Or just a direct, we’re going to smash and directly impart the kinetic energy into the surface of the planet, which is actually a bit worse.
Fraser Cain: Right. And if it hits the ocean, also not great because then it can cause localized tsunamis which can inundate the, uh, the shore.
Dr. Pamela Gay: So, so, you know, tell you Binsk was, I think a 17 meter asteroid, anything below 20 meters is going to do no worse than blasting out a whole lot of windows with localized damage. The level of like, we shall dent up your car or put a hole in your roof, but it’s the kind of stuff that apparently also starship will cause if you are beneath the starship that explodes. So pick your danger.
No, no. Uh, yeah. So it’s the kind of thing that is a apparently acceptable level of danger.
Um, and if you get far enough below 20 meters, it just burns up in the atmosphere. We are lucky enough to have this super thick atmosphere that frictionally heats and destroys a lot of falling rocks.
Fraser Cain: Yep. Now I want to talk about how astronomers find these things and figure out those probabilities, but it’s time for another break and we’re back. So how do astronomers find asteroids like this?
Dr. Pamela Gay: We are very good at recognizing asteroids could strike. The dinosaurs had a really bad day. We do not wish to have the same experience the dinosaurs had.
So we keep developing new surveys, new telescopes. Uh, currently the leading, uh, asteroid finding systems are the asteroid terrestrial impact last alert system. This is Atlas.
It is a robotic astronomical survey that is out there basically looking night after night with half meter telescopes to see what specks of light are on the move. And it was Atlas that discovered why are four on December 27th, a couple of days after its closest approach to the earth and, uh, based on how the specs of light are moving, we start to calculate orbits and, uh, then do a couple of different things, both, uh, getting other telescopes around the world pointed at these objects to confirm the orbits and, uh, folks also start going through archival imagery, looking to see if they can confirm or deny past locations of these space rocks.
Fraser Cain: And we’ve been chatting about this, I guess, in the science communication community, we’ve been, the news media has been reporting this. I feel like we’ve been on this for about two weeks. Yes.
At this point. And when it was first found, it was a 1% and then it was one point, whatever. And then it was 2.3 and then it’s 3.1. 3.1. Yeah. So why is the percentage going up?
Dr. Pamela Gay: So this cool adventure we’ve been on where it was getting more and more and more ever so slightly likely to hit us, I have to admit to being team asteroid, um, it was because I live on this planet too, Pamela.
Fraser Cain: You can’t use an asteroid to solve all your problems.
Dr. Pamela Gay: I wanted to move it. I wanted to have an excuse to move it.
Fraser Cain
All right. We’ll get to that. We’ll get to that.
Dr. Pamela Gay: All right. All right. So, uh, team asteroid.
Um, so what had happened was they calculated what are all the possible orbits that could fit the, uh, observations we have right now, which are kind of noisy, kind of, of not ideal because the timeline is too short. And then they started going back through archival data and saying, okay, this is an excellent orbit. Was the asteroid here?
Shoot. It wasn’t. When you don’t find the asteroid along the good orbits that eliminates the good orbit possibilities and increases the bad orbit possibilities.
Fraser Cain: Okay. So, so there, there, they find the asteroid and they find its trajectory and then they go back through archival data to see if it, if, if that, as soon as you can run that clock forward or backward and then see if it was in one of those things. And it, and if it isn’t there in the, in the safe ones, then you’re left with the unsafe ones.
Dr. Pamela Gay: And so they’d found it in Subaru archives. I, they were looking in other archives as well and it wasn’t in any of the good places. The asteroid did not go to the good place.
And because we don’t have complete coverage of the sky every night across all the decades, especially not with the big telescopes capable of seeing the small rocks, all we could say was these good orbits are eliminated. We can’t check the other orbits and we can’t check the bad orbits. So here we are with the increasing probability of impact.
Fraser Cain: I, I had no idea that that was the mechanism. That’s really interesting. Okay.
And so why then is the, is the, the chance going down? Are they also not finding it in the bad orbits?
Dr. Pamela Gay: So it, it, the moon got in the way. There was this window of time where, because we had a bright moon in the wrong part of the sky, I, it was just not possible to get the kinds of data that would tell us, no, we’re safe. So now that the moon is back down to a quarter phase rising at midnight, they’re able to get more data and that more data is giving us a better and better outlook for the future.
Now time has been granted to Andy Rivkin and his team to go ahead and use the James Webb Space Telescope to look at this asteroid next month, which will be March as of when we’re recording this in February. And that will hopefully tell us how big the asteroid is, further refine the orbit. And right now, like I said, we’re at only 1.5%. So it’s still a Torino scale three, keep your eyes on it, folks, be alert, but it will probably go down.
Fraser Cain: Right. That the Torino scale, this is that essentially asteroids of concern. If they’re bigger than about 20 meters, then they get to, and they have a chance of hitting earth at some point in the future, then they get to go on the Torino scale.
And then the question is, what are the chances? What is the scale of the impact? And then you, you get a placement.
And I think the highest ever was Apophis at like four and then it lost its ranking and went back down to zero. And now, uh, YR4 has taken a nice solid three on the Torino scale, but we will expect almost certainly that it is going to drop back off the scale and we’re gonna have to look for something else to be, uh, the dangerous asteroid of the, of the future. All right.
So next I’ve been promising, I want to talk about mitigation and we will talk about that in a second, but it is time for another break and we’re back. All right. Now I will allow a conversation about the mitigation of team asteroid.
Let’s say that in fact, the numbers go higher and higher and higher, and it gets to a point where space agencies are concerned that there’s a pretty good risk that this is going to hit us or come dangerously close. What could we do to stop this?
Dr. Pamela Gay: Well, we know thanks to the DART mission that we do have the ability to slam heavy objects into space rocks and cause their orbits to change. And from beginning of construction to launch was only about three years for the DART mission. So we have time, even if we wait until 2028 to figure out just how bad it’s going to be to, we have time to launch something, to slam into it and move it.
Now I’m hoping that we don’t wait until 2028 to figure out if we’re going to start launching missions and what’s cool is there’s lots of different possibilities. We were already starting to think through how are we going to observe Apophis in all of its glorious detail when it comes past us on April 12th, 2029. Apophis is a larger asteroid.
That’s how it made it to level four on the Trina scale. It’s going to be so close to the earth on April 12th, 2029, that we’re going to have weather satellite images looking down at our planet from geosynchronous orbit that show an asteroid passing between those weather satellites and our planet. It’s going to be a daytime visible object.
It’s kind of awesome.
Fraser Cain: You’ll be able to walk outside and watch it go by.
Dr. Pamela Gay: Uh-huh.
Fraser Cain: Yeah.
Dr. Pamela Gay: Uh-huh. Now for us, no, we’re on the wrong continent.
Fraser Cain: Right.
Dr. Pamela Gay: I’m probably going to have to travel for this. I feel obligated by the universe to go see this with my own eyeballs.
Fraser Cain: Wow. But like binoculars in the right part of earth watching it go by. It’s going to be a few tens of thousands of kilometers.
Dr. Pamela Gay: A space rock.
Fraser Cain: Going past the earth. And it’s big, way bigger than YR4. YR4 is small and so of less concern.
So let’s say that we wanted to quickly accelerate the construction of a spacecraft and we launch it. When is the best time to do that? Do we do this now before it does that flyby in 2028 and gets its orbit tweaked?
Or do we wait until 2028 when we know we have a better idea of what its orbit is going to be? And it’s also, it’s close. So we can reach out and smash into it.
Dr. Pamela Gay: So you want to try and deflect something as early as possible to give the effects of what you do the greatest opportunity to propagate through time. If you think about it, if you deviate a bullet just a tenth of a degree and you’re a couple of feet away from someone, please do not do this, a couple of feet away from a target, you’re still going to hit the target. But the further away you are, the more that deviation causes you to be more and more off center.
So our planet is a whole lot bigger, but the chances of impacting require at a great distance for the accuracy of the trajectory to be just so. So the further away in time you are, the more the change you make has a chance to keep an impact from happening. I would personally say, wait until we get the JWST data.
This is what Andy Rifkin was saying is definitely currently NASA’s discussion. Wait until we get the JWST data. Based on that, figure out what kind of a mission makes sense.
I think we definitely need to plan something to chase this sucker down and observe it. Unfortunately, 2028, it’s on an elliptical orbit. Our next closest approach, it’s going to be tens of millions of kilometers away, which is not friendly.
But we should definitely plan to launch something and be prepared for anything. Let’s do science, people. Let’s do science.
Fraser Cain: Right. It’s an incredible opportunity to watch how the gravity of the Earth deflects the orbit of an asteroid when it’s doing this flyby. It’s the same priority that you’re getting with asteroid Apophis with the updated version of OSIRIS-REx, that it’s going to be following Apophis.
It’s going to watch as this asteroid gets deflected by the gravity of the Earth. That’s going to tell it about the composition of Apophis. If we could do the same thing with YR4, then we’ll have two data points.
Watching as these asteroids are deflected by the Earth teaches a ton about this. What are the risks? I mean, if we attempt a deflection of YR4, how could it go wrong?
Dr. Pamela Gay: Well, there’s always the possibility that the spacecraft goes stupid, and instead of making it less likely to hit us, it instead makes it more likely to hit us. This is why you don’t try and deflect something that isn’t already going to hit you.
[Speaker 3]
Right.
Dr. Pamela Gay: Because if it’s already going to hit you, pretty much however you deflect it, it’s going to miss you. If it’s just going to come uncomfortably close, there’s the chance that you take it from uncomfortably close to a direct hit. So do not try and move something that’s not already going to hit you.
Fraser Cain
And the other possibility is that we fragment it, that we smash into it, turn it into a hail of particles, and now each one of those enjoys its own risk chance of hitting Earth or not. And so you’re actually sort of turning it into a shotgun blast for that next orbit.
Dr. Pamela Gay: Now, the thing is, this is a smaller object. Like I said, it’s give or take the size of a 747. Anything under 20 meters is not that big of a deal.
So if we take something that is 80 meters across and we fragment it, as long as those pieces are under 20 meters, we’re just generating a lot of heat, which is annoying and problematic. But we already have a lot of heat hitting the atmosphere from other space rocks. I’d rather fragment something this small than not, I guess.
Fraser Cain: Right, right. And I know that there’s a great article from Ethan Siegel that came out just a couple of days ago where he did some of the math. And it wasn’t as satisfying as I was hoping, that even if we build something like DART or maybe even like a super DART, something that’s like 1,000 kilograms, we slam it into this asteroid as soon as possible, we just get a reduction of the risk by, you know, something that becomes a lot more satisfying.
We knock away the 1% chance down to zero. We knock a 3% chance down to one. It’s not like we know that we’re going to make this dramatic change and it turns what is a risky space rock into something that is absolutely safe.
And it’s assuming a perfectly elastic collision. All of those still don’t get you, you are 100% safe now. They get you, you are safer.
Dr. Pamela Gay: One of the cool things about these is it’s not just a matter of, is it an elastic or inelastic collision? Is it a collision where the thing you strike it with sticks or bounces off completely and transfers all of its momentum? As we discovered with the DART mission, if you hit something that’s going to fall apart, the fact that you have a bunch of material flying away causes the main chunk to accelerate away even faster.
So you have this neat additional way of causing things to be on a less deadly trajectory. Now, again, you don’t want to move something unless it’s directly going to hit you because the probability that you’re going to make things worse is non-zero. If it’s already going to hit you, you’re probably going to make things better.
So pick your battles.
Fraser Cain: Right. So right now, should you panic? Absolutely not.
Now, when should you know to panic? 2028. 2028.
All right. So you have to wait. And we obviously, we’re going to update you as, as we get closer, either when it goes completely down to zero and, and even they know the 2028 flyby is going to be fine.
But after 2028, so we’ll tell you when to panic. But until then, please don’t panic. Don’t worry.
This is a tremendous science opportunity and is a great example of, yeah, of, and don’t let Pamela’s apocalyptic fantasies, you know, kill you.
Dr. Pamela Gay: I want to move it. I want to see the world come together. To cheer on the little spacecraft that moved the space rock.
I want global science. Yeah.
Fraser Cain: And there are multiple teams. So there is a team from the European space agency that has already come together to develop a working group to think about this and a separate team from China that is doing the same thing. And they’re already having collaborations between the two groups.
And so we could, we could absolutely see no matter what, some kind of spacecraft, maybe a international collaboration, going to check it out at the, as a scientific interest or to actually move it. And so, so stay tuned. We will keep you posted as, as progress continues.
All right, Pamela, thank you so much. And what have you got for us now?
Dr. Pamela Gay: I, I, I just want to take this moment to say thank you to all of our patrons out there. And this week we would like to thank Abram Cottrell, Alexis Bourre, Anthur Levesval, Bart Flaherty, Briznik, Brian Cagle, Burry Gowan, Daniel Donaldson, Daniel Knighton, Dwight Ilk, Felix Gute, Galactic President, Scooper Star, Mick Scoopsalot, Georgie Ivanov, Greg Davis, Greg Veild, J. Alex Anderson, John Baptiste Lematne, Joanne Mulvey, Jonathan Poe, J.P. Sullivan, just me and the cat, Kim Baron, Les Howard, Lou Zeeland, Marco Arasi, Matt Rucker, MHW1961, Super Symmetrical, Mike Husey, Nick Boyd, Paul D. Disney, Paul Esposito, Pauline Middlelink, Peter, Philip Walker, Planetar, R.J. Basque, Robert Cordova, Ruben McCarthy, Scone, Sergey Manalov, Simon Parton, Stephen Mueller, or Miller, Stephen Miller, Tim Garish, and Zero Chill. Thank you all so much. And if you too would like an opportunity for me to mispronounce your name, I am so sorry, everyone.
You really want that. Thanks, everyone.
Fraser Cain: And we’ll see you next week.
Dr. Pamela Gay: Bye-bye. AstronomyCast is a joint product of Universe Today and the Planetary Science Institute. AstronomyCast is released under a Creative Commons attribution license.
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