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On December 27, 2024, astronomers at the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Chile discovered a previously unseen asteroid on a potential collision course with Earth. The space rock, dubbed 2024 YR4, has an estimated diameter of between 130 and 300 feet, and it has the highest impact probability of any asteroid since humanity started such tracking.
It’s not exactly a Seeking a Friend for the End of the World type situation, but it is cause for scientists to pay attention. If 2024 YR4 is headed our way, we might be able to use technologies similar to NASA’s DART mission to do something about it.
Over the last several weeks, conversation around 2024 YR4 has been frantic, as scientists race to learn more about the asteroid and figure out whether it’s going to hit us or not. We know it’s going to be in the relative vicinity of Earth in December 2032, but there’s too much ambiguity in its orbit to know if it will strike or fly safely past. Now, scientists are planning multiple observations with the James Webb Space Telescope (JWST), the most powerful telescope ever built.
How to figure out if an asteroid is going to hit the Earth
When 2024 YR4 was first announced, it had an impact probability of 1 in 80, about 1.2%. Over the following days, astronomers made continual observations, learning more about the asteroid and how it’s moving. As our models improved, the probability of impact increased, first to 1 in 62, then to 1 in 32, the impact probability getting as high as 3.1%.
That makes it the most likely impactor of this size we’ve ever seen in advance, but the odds are still low and they’re likely to fall to zero soon. The reason the numbers keep changing is because of the way impact probabilities are calculated and uncertainty in where 2024 YR4 is going.
Imagine firing a slingshot into the distance and trying to figure out exactly where your pebble will land. Shifting your orientation just a fraction of a degree will cause your missile to land in a drastically different place. We don’t know where it’s going to land because we don’t know the precise trajectory it’s already on. Instead, astronomers calculate a range of trajectories based on the information we have and extrapolate them into the future. The impact probability depends on how many of those potential paths intersect the Earth. If, for instance, there are 100 possible paths and 5 of them intersect the Earth, then the impact probability would be 5%.
As a result, sometimes impact probabilities rise dramatically as uncertainty decreases. That happens if the pile of possible paths gets smaller while the number intersecting Earth remains the same. Conversely, as the pile of possible paths shrinks, it might slide away from the Earth, reducing the number of paths intersecting Earth and causing the probability to plummet. That’s what happened on February 16, when the impact probability dropped from 1 in 32 to 1 in 67.
NASA’s JWST will study potentially deadly asteroid 2024 YR4
Right now, asteroid 2024 YR4 is heading away from us and getting dimmer in the night sky. Astronomers only have until April to observe the asteroid from Earth, after which it will be too far away to see with ground-based telescopes. We won’t be able to see it again until 2028, when it comes back around on its roughly 4-year orbit. That’s where JWST comes in.
The size and composition of 2024 YR4 aren’t wholly known, and they will influence how much damage is done if it hits. Considering its size, if 2024 YR4 does strike, it’s likely to cause an airburst, exploding in the atmosphere. If that happens over the ocean, the most likely scenario, we’re unlikely to suffer any significant consequences. If it happens over a city, it could cause some regional damage ranging from blown out windows to destroyed buildings, according to NASA.
Astronomers have two rounds of observation planned, first in March of 2025 and then again in May. Using the onboard Mid-Infrared Instrument (MIRI), JWST will offer a better estimate of the asteroid’s size by measuring infrared light, rather than reflected visible light. With its Near-Infrared Camera (NIRCam), it will help to calculate the asteroid’s position, determining whether it will strike or not.
Check out Seeking a Friend for the End of the World, now available from Universal Pictures Home Entertainment.
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