What are the chances of an asteroid hitting earth in 2032?

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Hello, and thank you for downloading the More or Less podcast with me, Tim Harford.

We're the program that looks at the numbers in the news and in space.

On December the 27th, 2024, when many of us were still in a mince pie coma, astronomers in Chile discovered an object in space with a trajectory that was potentially a bit too close for comfort.

The object was an asteroid, which they called 2024 YR4.

Cute.

As you probably know, asteroids are basically space boulders and quite probably dinosaur killers.

News agencies and social media went wild trying to predict which cities it would hit and what the damage would be.

Potential danger in space and it's on a collision course with a city-destroying asteroid that could smash into Earth in a moment.

And wipe out an entire country in a few seconds.

People certainly lost their cool.

So what was the likelihood of the asteroid actually hitting Earth?

It must be a pretty high percentage to get people so excited.

1%.

The initial finding was a 1% likelihood of hitting Earth.

So why was this such a big deal?

Partly because a 1% chance of something really bad is still quite bad.

But mostly because shortly after discovery, this 1% likelihood was upgraded to 3%.

Only one other asteroid in recent times has come close to that.

That one won't hit us, don't worry.

You should be able to see it pass harmlessly over in 2029.

But sometimes asteroids do hit.

For example, in 2013, when an asteroid hit Chelyabinsk, Russia.

or the Tunguska event of 1908.

Also, in Russia, it seems asteroids really hate Russia.

So what are the odds that asteroid 2024YR4 could give us a close encounter of a crashing into our planetary kind?

We have a lot of asteroids and comets in the solar system.

We actually catalogued more than 1.4 million of those.

Some of them have the potential of coming close to the Earth.

My name is David Farnocchia.

I work as a navigation engineer at NASA's Jet Propulsion Laboratory and I track asteroids and comets for my job.

Asteroids are tracked using data gathered by astronomers around the globe.

They look for the infrared signal of a nice warm asteroid or by light reflected off an asteroid's surface.

They then calculate the speed by measuring how quickly they go past stars.

As stars don't really move, they're a good reference point.

Most of us are familiar with asteroids from disaster movies such as Armageddon, Deep Impact, and Ice Age 5 Collision Course.

Although we haven't had to tackle any Hollywood-sized asteroids as of yet, objects entering Earth from space aren't as uncommon as most of us would believe.

Space is mostly empty, but there is material and Earth is reached by about 100 tons of interplanetary material pretty much any given day.

That's the typical rate.

But most of that is dust and so we don't even notice.

It's too small to make any effect.

Some of these objects include asteroids, which are among the oldest objects in the solar system.

They are kind of the leftovers of the formation process of the solar system.

When the solar system formed, there was a lot of material going around.

A lot of that material kind of got back together and formed the planets, but some of that material remained between the orbits of Mars and Jupiter.

Jupiter was pulling enough with its gravity to prevent the formation of another planet.

between Mars and Jupiter.

And so we were left with a bunch of rocks in that ring between Mars and Jupiter.

Occasionally some of these asteroids escape this interplanetary ring road due to a mechanism called resonance

which is similar to what kids do when they go on a swing right if they go on a swing and they move their legs with the right timing as the swing goes up and down they start going higher and higher.

And so what happens is that if you are in a resonance that your motion has the right timing compared to that of Jupiter or another planet, your orbit kind of gets excited and you might get injected into the inner solar system.

Having these intrepid little asteroids enter Earth's atmosphere isn't as rare as you might think.

Smaller asteroids, or fragments of asteroids measuring less than a meter across, hit the Earth's atmosphere almost daily.

Asteroids measuring a few meters across pass between the Earth and the Moon several times a month.

Most don't actually enter into our skies, but some do.

We've had in 2024 four objects of a couple meters in size that were detected prior to reaching the Earth.

Those were completely harmless.

They burned up in the atmosphere, but it kind of proved the concept that impacts are part of the evolution of the solar system or part of our experience in space.

What about bigger asteroids?

Thankfully, they are a much rarer occurrence.

We don't have much evidence for larger asteroids hitting Earth, but scientists have used crater formation rates on the Moon to calculate that that over the last 600 million years, the Earth has been struck by around 60 objects whose diameter was 5 kilometers or more.

That is, 60 different occasions when quite a lot of the creatures on Earth at the time had a very bad day.

2024 YR4 is not as big as this.

Its diameter is thought to be between 40 and 90 meters, about the size of the Statue of Liberty, either with or without the plinth.

The impact of an asteroid like this wouldn't cause mass extinction, but it could wipe out a city.

So what are the odds of it actually hitting?

Right now it's 5 10 to the minus 7 so that would be 5 in 10 million.

Those are the odds.

Very very small.

Very small indeed.

So why did everyone get so excited?

We actually had a much larger impact probability a while back.

It reached the peak of 3.1%, percent which is the largest impact probability ever recorded for an object of this size 3 percent that sounds like time to get serious but wait that is still a 96.9 percent chance that it won't hit us still i prefer the much longer odds we now have so why is the collision now thought to be so much less likely and why did the risk initially rise before it fell

initially we only had limited observational data.

We saw that the impact in 2032 was a possibility, but the uncertainty was so large that the probability of actually hitting the Earth was very small.

As we gathered additional observational data, this uncertainty in position for the asteroid in 2032 became smaller, but the Earth remained inside the swath of possible positions for the asteroid.

And so the probability went up because the Earth was occupying a larger fraction of that uncertainty.

Think of it as kind of like an intersection, a road junction, such as a crossroad.

We know where the Earth is and how the Earth travels.

We know at what time and what point the Earth will travel into the middle of the intersection, but we can't predict exactly the asteroid.

As the weeks have gone by, they've collected more and more data, allowing them to more accurately measure the asteroid's speed, its path, and the likelihood of a collision.

We realized that the object was going to go through it at a different time than the Earth.

Excellent news.

So what percentage are we at now?

It's 99.999999, whatever.

It's not going to hit.

Despite it very likely no longer being a threat, Davide and the team at NASA continue to watch 2024 YR4

and other asteroids.

So we track all of them.

Every day, we have a bunch of objects that are discovered.

Those are new.

They're added to the catalogue.

And when that happens, we take a...

look right away and see whether they might be possible impact sometime into the future.

With so so many asteroids out there, is Davide worried about an imminent impact?

Asteroid impacts for asteroids that are capable of causing substantial damage are really unlikely.

It's not something that people should lose their sleep over.

And with those words of reassurance, we leave you.

Thanks to Davide Farnochia and all the people at NASA who are keeping an eye on the skies.

If you have any questions or comments, please do write into us at more or less bbc.co.uk.

We will be back next week.

Until then, goodbye.

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