Don’t look up: is an asteroid heading for Earth?
15:43 Share

This is The Guardian. Science Weekly is supported by Cambridge University Press, publisher of Brain Boost, healthy habits for a happier life. By adopting good lifestyle habits, everyone can live a fuller life. But while many focus on their physical health, they rarely consider improving brain health. But that's every bit as important.

Brain Boost, Healthy Habits for a Happier Life, presents clear guidance on leading a more fulfilling, vibrant life by improving brain fitness, thinking ability, creativity, mood and well-being. The book's authors are experts in neuroscience...

and it contains evidence-based advice rooted in science. Find out more and order your copy from cambridge.org slash brainboost. And Science Weekly listeners can enjoy 20% off by using the code BOOST20 at the checkout. That's the word BOOST, then the number 20. Science Weekly is supported by King's College London. Do you accept the world as it is?

Or do you ask questions to change it? Perhaps questions like, is net zero achievable in our lifetime? The Net Zero Centre at King's College London nurtures and facilitates discovery and research to address how to decarbonise our society. It uses King's strengths in academic subjects as well as partnerships with government and industries to find solutions for environmental sustainability.

The Net Zero Centre will foster the next generation of King's changemakers. Every change starts with a question. Find the right questions at King's. Search King's College London. Accept or question today. It's a Hollywood plot for the ages. A giant asteroid is heading towards the Earth and humanity has to find a way to stop it.

I heard there's an asteroid or a comet or something that you don't like the looks of. Tell me about it. You got 20 minutes. It's what we call a global killer. The end of mankind. Doesn't matter where it hits. Nothing would survive, not even bacteria. My God.

Thankfully, fiction is yet to become reality. Although last week and for the first time ever, an asteroid really did trigger global planetary defence procedures. Did you know there's an asteroid headed towards Earth and there's a more than 1% chance of an Armageddon-style threat to the planet in 2032?

Known as 2024 YR4, the asteroid appears to be on an orbit that will bring it very close to Earth, with a potential arrival date set for 22nd December 2032.

We think it's around 50 meters across, about half of a soccer pitch. And an object that size is what exploded in the air over Tunguska, Siberia in 1908. It wasn't observed by any humans that we know of, but some years later, when an expedition was able to reach it, they found flattened trees for hundreds of kilometers in the area.

Richard Binzel is a professor of planetary sciences at the Massachusetts Institute of Technology and has a special interest in asteroids and the hazards they compose.

If an asteroid the size of 2024 YR4 did hit, it could cause catastrophic damage on the city scale. Right now the chance of that happening is estimated at 2.3%. Or, but another way, there's a nearly 98% chance it'll barrel right past. But despite the low odds, astronomers have swung into action to monitor 2024 YR4's progress and precisely pinned down its path.

I like our chances. In all likelihood, this object will go away. So today, what happens when we discover an object that might crash into our planet? I'm the Guardian science editor, Ian Sample, and this is Science Weekly. Science Weekly.

Richard, last week we heard about this 40 to 100 metre wide asteroid, 2024 YR4, that triggered these global defence procedures. When was it first spotted? The asteroid 2024 YR4 was first spotted in December of 2024, and that's why it has that number. And it was a telescope in Chile that is routinely scanning the skies for asteroids that can come close to the Earth.

They discover dozens a night, if you will. And it was only later as we were able to track its orbit a little bit further that we discovered when we project way far into the future, we cannot rule out that the Earth could be in its path.

Once an asteroid is discovered, particularly one that has an interesting orbit, shall we say, astronomers all over the world then start paying attention and trying to get their own observations. In the case of 2024 YR4, it's a very faint object, so it takes fairly large telescopes, fairly sophisticated equipment to track it, but those data are all public.

And then agencies at NASA and the European Space Agency take all those measurements from telescopes all over the world and use those to solve for the orbit. So right now, it's all about trying to reduce the uncertainties around the path of the asteroid.

How difficult is it to get an accurate picture of exactly where this rock will be years into the future? It is a bit of a challenge to project that asteroid orbit forward for decades and decades. It's like trying to predict the path of a hurricane. The day you discover there's a low-pressure system in the Gulf...

it just becomes more and more uncertain the further and further you project. And so you just simply have to make measurements, and then ultimately, over time, you can see where it's going. So that's really the situation we're in for this asteroid. We have just barely seen a little tiny piece of the entire orbit. ♪

So the risk for 2024 YR4 currently stands at about 2.3% or a 1 in 43 chance of impact, which makes it a 3 on something known as the Torino Impact Hazard Scale.

Now, Richard, you're the inventor of the Torino scale. Tell me about it. What does a three mean? Yes, so the Torino scale is a 10-point scale from zero to 10. If we know an object is certain to hit the Earth and it reaches the level of 8, 9, or 10, where 10 would be the experience of the dinosaurs,

It's very rare that an object ever reaches above zero or one on the Trino scale. And so the lower categories simply try to explain what are the probabilities and what is the likelihood that with new data, the asteroid will no longer be a problem.

Is it fair to say that part of the value of the Torino scale is to keep journalists like me from getting a little bit too excited when they're writing about asteroid near-misses? Because, you know, it's quite easy for these things to be written in a pretty alarmist way. Yes, absolutely. The goal of the Torino scale was to provide a

objective description of what's being discovered, largely for science journalists as a media communications tool. You know, if you're in California and you say there's going to be a magnitude three earthquake tomorrow, you don't blink. And that may be what comes to pass as we discover more and more asteroids and they get to zero, one or two.

or two, maybe three on the Torino scale, that may become a rather common occurrence because our surveys are getting better and better. We're starting to discover more and more objects. 2024 YR4 may be pretty low on the scale, but its non-zero chance of impact activated two UN-endorsed global asteroid response groups.

In the highly unlikely event that 2024 YR4's risk of collision goes up rather than down, the Space Mission Planning Advisory Group would propose plans to intervene, like sending a spacecraft to deflect the asteroid's path. It is a first for humanity. NASA successfully changed the path of an asteroid.

The space agency used a spacecraft to hit the asteroid Dimorphos. It's the first time it's ever been done and it's hoped that it'll teach us how to change the speed and path of future asteroids and planets.

Since its inception, the only asteroid that has ever been ranked higher on the Torino scale than 2024 YR4 is 99942 Apophis, named after the Egyptian god of chaos. In 2004, we discovered an asteroid that became named Apophis. And it was a very similar situation to what we see for the current asteroid discovery.

In that initially, when we had only a tiny piece of the orbit, just a little bit of the pathway, when we projected that forward, in fact, into 2029, we couldn't be sure that it was going to miss the Earth. And because this object was a little bit larger than the one we're talking about now, it got a four on the Trinit scale instead of a three.

But as we got more and more measurements, we could precisely project the orbit forward and be certain that it was going to miss the Earth. That's why it's now zero on the Torino scale.

And it's exactly the same sort of story that we expect to evolve for 2024 YR4. And since its discovery, as you say, astronomers have worked out a pretty accurate orbit for Apophis. When is it expected to hurtle past the Earth and how close is it going to get? So Apophis is a stadium-sized asteroid and we know it will safely pass the Earth and

on April 13th, 2029. And nature has a sense of humor because that April 13th is a Friday. The mist distance of Apophis will be just one-tenth of the distance to the moon.

So it will come closer to the Earth than the geosynchronous satellites are to the Earth. And when Apophis comes by and passes inside or closer than those satellites, Apophis itself will be passing across the northern hemisphere, and most of these satellites are down at the equator. So there's very little risk or very little likelihood of any satellite being involved or having any consequence of having this asteroid go by.

And this will be near enough that people in Western Europe and Africa will have a pretty good view of it shooting past without the need for telescopes or anything like that, which is pretty exciting. But this kind of proximity must be thrilling for scientists like yourself too, right? I mean,

What kinds of things could we learn from this close encounter? As scientists, we're incredibly excited about this asteroid opportunity because Apophis is going to come so close to the Earth that the Earth's gravitational forces and Earth's tidal forces are going to act on the asteroid. And they're going to change the way the asteroid moves through space. They're going to change the way it spins and tumbles along in its orbit.

And we don't know how the asteroid is actually going to respond to the Earth's gravitational torques or gravitational tugs because we don't know how the asteroid is put together.

And so if we can measure and watch how this asteroid responds to the stress that the Earth's gravity puts on it, we're going to learn how these hazardous asteroids are put together. It's terra incognita. We have never yet been able to probe the inside of one of these hazardous asteroids.

And it could be some of the most valuable information we ever have if in some future case we actually had to seriously push on an asteroid like Apophis. Are any of the space agencies looking to take advantage of this and visit Apophis as it comes by? There is a NASA mission called OSIRIS-REx which recently returned an asteroid sample to the Earth.

And that spacecraft has been redirected to intersect with Apophis in mid-2029. And so the laws of orbital mechanics and the available fuel on board OSIRIS-REx, which has now been renamed OSIRIS-APEX, where the APEX is Apophis Explorer,

The OSIRIS-APEX spacecraft won't be able to get to Apophis until after it has gone by the Earth. So we'll see all the after effects, but that's not going to help too much if we don't have measurements of the before. And in this case, the European Space Agency is coming forward in a partnership with NASA to propose a mission called RAMSIS-2.

So, it has an Egyptian name. This will arrive at Apophis before it encounters the Earth. So, it's a really wonderful partnership between two space agencies. Richard, we have a little more than four years until April 13th, 2029. I presume you'll be planning to be outside to watch it streak past. Where are you thinking of going to get a good look? I don't want to give it away because everyone will go there.

Right now, I'm actively working with international agencies and international scientists, formulating workshops where we get together and exchange our knowledge about what we think might happen with Apophis and how we're going to measure it. But probably by 2029, I'll be sitting back, maybe on a beach somewhere, and watching it go by in the serene calm of an oceanside seat.

Well, Richard, make sure that you've got Wi-Fi on this beach because I think it'd be really good to have you back on to get your sense of what it was all like. All right. Well, to be continued then. A big thanks to Professor Richard Binzel. Do you have more questions about asteroids? Or would you like to know exactly why placebos work even when we know we're taking them? Or perhaps you want to find out what earthquakes tell us about the planet's core?

We love the questions we receive from you for our Getting Healthy in 2025 specials and want to make more episodes that bring you answers backed up by science. So please let us know what you want to know. Just email scienceweekly at theguardian.com.

And if you're after something to listen to next, I'd like to recommend today's episode of our sister podcast, Today in Focus. Helen Pidd hears why an expert panel of scientists have concluded there's no medical evidence to support Lucy Letby's conviction and whether that will affect her chances of an appeal.

Just search for Today in Focus wherever you're listening to this podcast. And that's all for today. This episode was produced by Madeline Finlay. It was sound designed by Joel Cox. And the executive producer is Ellie Burey. We'll be back on Thursday. See you then.

This is The Guardian.

Science Weekly is supported by Cambridge University Press, publisher of Brain Boost, healthy habits for a happier life. By adopting good lifestyle habits, everyone can live a fuller life. But while many focus on their physical health, they rarely consider improving brain health. But that's every bit as important.

Brain Boost, Healthy Habits for a Happier Life, presents clear guidance on leading a more fulfilling, vibrant life by improving brain fitness, thinking ability, creativity, mood and well-being. The book's authors are experts in neuroscience and it contains evidence-based advice rooted in science. Find out more and order your copy from cambridge.org slash brainboost.

And Science Weekly listeners can enjoy 20% off by using the code BOOST20 at the checkout. That's the word BOOST, then the number 20. Enjoying this podcast? Then we think you might love the Audio Long Read, the podcast of The Guardian Long Read, with episodes about caffeine addiction, the secret life of saints and Britain's strangest pub chain,

The Long Read offers great stories and big ideas. Follow the Audio Long Read wherever you get your podcasts.