For about a week in February 2025, a lot of otherwise sensible people looked up asteroid deflection missions on their lunch break. The object was called 2024 YR4, the impact probability climbed to 3.1 percent, and that was, at the time, the highest figure ever recorded for a rock of that size.
It is over now, and it has been over for a while, but the file has finally been closed on both of the scenarios that made it interesting. The asteroid will not hit Earth. It will also not hit the Moon, which was the quieter and genuinely more likely of the two possibilities. What is left is the part actually worth remembering, and it is a sentence from an MIT planetary scientist rather than a probability.
The short version
- The object: 2024 YR4, discovered in late December 2024, measured by the James Webb Space Telescope at roughly 53 to 67 meters across, about the height of a ten story building
- The scare: Earth impact odds peaked around 3.1 percent in February 2025 before more observations cleared it within days
- The second act: attention shifted to the Moon, where the odds climbed as high as roughly 4.3 percent for December 22, 2032
- The resolution: Webb observations in February 2026 eliminated the lunar impact. Current projections have it passing about 13,200 miles from the lunar surface
- The takeaway: objects this size pass through the Earth and Moon neighborhood a few times a year. We have only recently been able to see them coming
How the number moved
The thing that made 2024 YR4 unnerving was not the peak value. It was watching the value go up. An impact probability rising day after day feels like a countdown, when in fact it is usually the opposite: it is the uncertainty region shrinking around a path, and Earth happening to still be inside the shrinking region.
Once the region shrinks past Earth, the number collapses to essentially zero, which is exactly what happened within about a week. This is normal. It is also, from a public communication standpoint, an almost perfectly designed way to cause panic.
What Webb actually measured
The interesting science here got much less attention than the odds did. Ground based telescopes could only bracket 2024 YR4 somewhere between about 40 and 90 meters, which is a frustrating range when the difference between the low end and the high end is roughly a factor of ten in energy.
Webb was pointed at it in early 2025 and returned a far tighter figure of roughly 53 to 67 meters. That made 2024 YR4 the smallest object Webb had ever targeted, and one of the smallest ever to have its size measured directly rather than inferred from brightness.
Two other findings came out of the same work and are more interesting than the size. The surface appears to lack fine grained regolith, the dust that coats most asteroids, and instead looks dominated by coarser rock. The likely explanation is that it spins fast enough to fling the fine material off. That is a real result about how small bodies behave, obtained entirely because a rock briefly looked like it might be a problem.
The “100 nuclear bombs” figure, translated
This comparison has followed 2024 YR4 through every round of coverage, and it is worth unpacking because it is simultaneously accurate and misleading.
| The claim | What is behind it |
|---|---|
| “As powerful as 100 nuclear bombs” | Estimates put the impact energy in the region of 8 megatons of TNT. Divided across typical modern warhead yields, you land near 100 |
| “City killer” | Fair. An object this size mostly detonates in the atmosphere. The damage is a blast wave over a metro area, not a crater |
| “World ending” | Not close. Extinction level events involve objects measured in kilometers, not tens of meters |
| Where it would most likely land | Water or empty ground. Roughly 71 percent of the surface is ocean and most of the land is not a city |
| Radiation | None. The nuclear comparison is about energy release only. There is no fallout from a rock |
The nearest real world reference point is Tunguska in 1908, where an object in a broadly similar class flattened something like 2,000 square kilometers of Siberian forest and injured almost nobody, because there was almost nobody there. That is the honest shape of the risk. Enormous local destruction, vanishingly small odds of it happening over a city.
The sentence that should outlive the panic
Richard Binzel, the MIT planetary scientist who devised the Torino scale in the first place, gave the framing that deserves to survive this news cycle. As he put it to Space.com, an object the size of 2024 YR4 passes harmlessly through the Earth and Moon neighborhood as often as a few times per year.
Read that twice. The rocks were always there. What changed is that we can now see them, sometimes years ahead, and calculate where they are going. Binzel’s other line lands the same point: the YR4 episode is the beginning of astronomers being able to spot these objects before they arrive, not evidence that the sky got more dangerous.
The correct emotional response, ranked
- Mild reassurance. A 60 meter rock was detected, tracked, characterized and cleared inside two years, twice
- Genuine interest. We now know what its surface is made of because it scared us into looking
- A little unease, but the useful kind. It was found in December 2024 for an approach in 2032. Eight years is enough warning. Eight months would not be
- Not fear. The probability is now effectively zero for both Earth and the Moon
Why the next one gets caught earlier
The detection story is the part quietly improving in the background. The Vera Rubin Observatory in Chile is built for exactly this kind of work, scanning the whole visible sky repeatedly and flagging anything that moves. On its first night of alert testing it generated about 800,000 alerts, which gives some sense of how much of the sky has simply never been watched carefully.
More detections will mean more objects appearing briefly on risk lists, more probability numbers going up before they go down, and more headlines that look like 2024 YR4. That is what success looks like. It is going to feel like the opposite.
One more thing about NASA headlines
The 2024 YR4 story got distorted mainly through compression, not invention. The real numbers were dramatic enough that they did not need help. But the appetite for space catastrophe stories is large enough that it does get fed with material that has no basis at all, which is how an entirely fictional NASA program convinced a lot of people that gravity was about to switch off earlier this month.
The tell is usually the same. Real planetary defense updates come with an object designation, a date, a probability and an observation source, and they get revised as data comes in. If a story about the end of the world has none of those things, it is probably closer to the 1960 paper that put doomsday on a Friday the 13th than to anything an observatory published.
As for 2024 YR4, on December 22, 2032, it will pass roughly 13,200 miles from the lunar surface, and almost nobody will notice. Which is the correct ending for this kind of story, and an unusually rare one.
