The impact odds for asteroid 2024 YR4 climbed to a record, then collapsed to zero — not because the rock moved, but because the uncertainty around it did.
JUNE 4, 2026 · 7 min read
What you need to know
In December 2024 a telescope in Chile found a 50-to-70-metre asteroid, 2024 YR4, on a path that brought it close to Earth and the Moon in December 2032. For a few weeks its chance of hitting Earth was the highest astronomers had ever logged for a rock that size. Then the odds vanished. This is the story of why the number rose before it fell.
— 01
THE STORY EVERYONE HEARD
A percentage that lurched, then disappeared.
Start with the thing people remember: a number that would not sit still. A few percent chance of hitting Earth. Then briefly higher — the worst NASA had ever logged for a rock this size. Then, inside a week, almost nothing. The risk slid across to the Moon, climbed back toward four percent, and in March 2026 went to zero there as well. Six readings of one threat, and not one of them held.
Read as a headline, it looks like indecision. An alarm raised, then a run of quiet corrections, then a shrug. A scare scientists kept walking back until there was nothing left to walk back from. By the time the all-clear arrived, the rock had become a punchline about overreaction.
Look closer and the rock did none of it. Across the full fifteen months, 2024 YR4 stayed on exactly the orbit it was already flying. Nothing about the asteroid lurched. What lurched was the size of the box astronomers had drawn around where it would be on 22 December 2032, and a probability is only a reading off the size of that box. Watch the box, and the whole scare reorganises itself.
Everything below takes that same sequence the public read as a walk-back and runs it the other way: a measurement getting sharper on a schedule, one telescope pass at a time. The scariest moment was not the moment of greatest danger. It was the moment of least light.
The public memory of 2024 YR4 is a number that scientists kept revising: a few percent chance of impact, briefly a record high, then quietly walked back to nothing. Read that way, it looks like a system that overreacted and then corrected itself. The rest of this issue argues it was the reverse — the asteroid never changed course; only how well we knew its course did.
— 02
A FIFTEEN-MONTH ARC
The number rises, migrates, then snaps to zero.
From a December 2024 discovery to a March 2026 all-clear, the recorded odds climb to a record on Earth, fall, jump to the Moon, climb again, and stop at nil. Read down the dates and one fact holds under all of them: the orbit is the same at every entry. Only the precision changes.
Dec 27 2024
Discovery — ATLAS, Río Hurtado, Chile.
The NASA-funded Asteroid Terrestrial-impact Last Alert System first reports 2024 YR4 to the Minor Planet Center. NASA places the station 'in Chile'; ESA names it Río Hurtado.
Feb 18 2025
Earth-impact odds peak at 3.1%.
For 22 Dec 2032 — 'the highest impact probability NASA has ever recorded for an object of this size or larger.' This is the high-water mark, set when the orbit was least constrained.
Feb 19 2025
Dark-skies observations cut the odds to 1.5%.
A single night of fainter-sky tracking nearly halves the Earth figure. The rock has not moved; the error box has shrunk.
Feb 24 2025
Earth ruled out — odds fall to 0.004%.
NASA concludes 2024 YR4 poses no significant threat to Earth in 2032 and beyond. A residual 1.7% chance of hitting the Moon remains.
Apr 2 2025
Lunar-impact odds rise to 3.8%.
JWST thermal data also pins the size at 53–67 m. The Moon now sits well inside the shrinking box, so the lunar figure climbs as Earth's falls.
Jun 3 2025
Lunar odds climb to 4.3%, then go dark.
The orbit is refined further and the Moon figure keeps rising. Soon after, the asteroid fades beyond reach of every telescope until a 2026 Webb window.
Feb 18 & 26 2026
JWST makes two decisive faint detections.
Among the faintest observations of an asteroid ever made, tracked against star positions fixed by ESA's Gaia mission. These pin the 2032 position two years before any ground telescope could.
Mar 5 2026
Lunar impact ruled out — odds to zero.
NASA and ESA announce 2024 YR4 will miss the Moon, passing more than 20,000 km beyond it on 22 Dec 2032.
— 03
THE OBSERVATION CAMPAIGN
Each pass buys precision, not a new orbit.
Here's the thing each observation actually did: it added photons against a known background, and every batch of photons pulled the box around the 2032 position a little tighter. So this panel just ranks that tightening, pass by key pass. It's an illustrative schematic, not data. The bars say how much each pass narrowed the orbit, not any published signal value.
SCHEMATIC — relative orbit-precision gained per observation pass, not published measurementstelemetry
acquiring4 bands
ATLAS optical discovery · Dec 2024ground · visible
22/ 100
JWST thermal (size) · Mar 2025space · mid-IR
54/ 100
JWST faint detections · Feb 2026space · near-IR
94/ 100
Gaia star catalogue · reference frameastrometric anchor
88/ 100
Source · Qualitative basis: NASA Webb blog (6 Mar 2026); ESA on the Gaia reference frame (5 Mar 2026). Bar values are editorial.
— 04
THE NUMBERS THAT MOVED
Six figures, and one of them is the rock.
Five of these tiles are probabilities, dates, and distances that moved as the orbit sharpened around the rock. Only the size belongs to the rock itself. Every note carries the date and source it came from.
ASTEROID 2024 YR4 · KEY FIGURES, DEC 2024 – MAR 2026
3.1%
Peak Earth-impact odds
18 Feb 2025 — 'the highest impact probability NASA has ever recorded for an object of this size or larger.' (NASA, 19 Feb 2025)
0.004%
Earth odds after resolution
24 Feb 2025 — NASA concludes no significant Earth-impact threat in 2032 and beyond. (NASA, 24 Feb 2025)
4.3%
Peak lunar-impact odds
3 Jun 2025 — the high point of the lunar figure; ESA later described it as 'around 4%.' (NASA, 5 Jun 2025; ESA, 5 Mar 2026)
53–67 m
Estimated diameter
From JWST mid-infrared thermal data, 26 Mar 2025. The one figure here that describes the rock, not our knowledge of it. (NASA, 2 Apr 2025)
>20,000 km
Miss distance from the Moon
ESA: more than 20,000 km. NASA: 13,200 mi (21,200 km) above the lunar surface. (ESA & NASA, 5 Mar 2026)
Dec 22 2032
Close-approach date
The single date every probability above was a reading for. (NASA 2024 YR4 Facts; ESA, 5 Mar 2026)
Sources · NASA Planetary Defense blogs (19 & 24 Feb, 2 Apr, 5 Jun 2025; 5 Mar 2026) · ESA Planetary Defence (5 Mar 2026) · NASA 2024 YR4 Facts
— 05
WHERE THE ROCK ACTUALLY GOES
The 2032 pass, drawn to clear the Moon.
On 22 December 2032, 2024 YR4 crosses the Earth-Moon system and clears the Moon by more than 20,000 km. The diagram below sketches that geometry so the clearance is visible. It is a schematic, not to scale. The only published quantity is the miss distance; the axis values are illustrative.
SCHEMATIC, not to scale — approach geometry for 22 Dec 2032. The sourced quantity is the >20,000 km lunar miss; coordinates are illustrative.apoapsis 60k km
Inbound60k km · 0 km dr2024 YR4 approaches the Earth-Moon system along the orbit it has flown since discovery.
Lunar plane38k km · 90 km drThe asteroid crosses the Moon's orbital distance — the moment the 4.3% figure was once a reading for.
Closest to Moon21.2k km · 150 km drNearest approach: more than 20,000 km clear of the lunar surface. NASA states 21,200 km. No impact.
Outbound40k km · 220 km drThe rock continues past the system and back into the inner solar system, unobservable again until 2028.
Source · Geometry illustrative. Miss distance: ESA ('more than 20,000 km') & NASA ('13,200 mi / 21,200 km above the lunar surface'), 5 Mar 2026.
— 06
WHY THE NUMBER WENT UP FIRST
The same sequence, read two ways.
A probability that climbs to a record and then craters can look like a system failing to make up its mind, when it is the ordinary signature of one doing its job. The whole difference is what you take the reading to be about: the rock, or the box drawn around it.
The Surface Read
The odds went up, then vanished — so the warning was overblown.
On its face, the arc is a walk-back. The Earth figure hit a record 3.1%, the risk crossed to the Moon and climbed past 4%, and then all of it evaporated. If the danger were real, the thinking goes, the number would not have collapsed. So the peak reads as an alarm, and the all-clear as a quiet retraction of it.
The Structural Read
The rock never moved. The uncertainty around it shrank.
Right after discovery, the asteroid's 2032 position was a long error ellipse, and the Moon sat inside it, so the odds were a few percent. Each observation narrowed that ellipse, until the Moon fell outside it and the odds snapped to zero. The number peaked when the orbit was least constrained. The orbit was least constrained when the asteroid was faintest. The peak measured how little light we had, not how close the rock was coming. NASA put it plainly: the update 'reflects improved precision in our understanding of where the asteroid is expected to be in 2032 rather than a shift in its orbital path.'
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New NASA Asteroid Observations Eliminate Chance of 2032 Lunar Impact — NASA Science · Planetary Defense blog.
science.nasa.gov · primary
Asteroid 2024 YR4 will not impact the Moon — European Space Agency · Planetary Defence.
esa.int · primary
Dark Skies Bring New Observations of Asteroid 2024 YR4, Lower Impact Probability — NASA Science · Planetary Defense blog.
science.nasa.gov · primary
Latest Calculations Conclude Asteroid 2024 YR4 Now Poses No Significant Threat to Earth in 2032 and Beyond — NASA Science · Planetary Defense blog.
science.nasa.gov · primary
NASA Update on the Size Estimate and Lunar Impact Probability of Asteroid 2024 YR4 — NASA Science · Planetary Defense blog.
science.nasa.gov · primary
NASA's Webb Observations Update Asteroid 2024 YR4's Lunar Impact Odds — NASA Science · Planetary Defense blog.
science.nasa.gov · primary
How NASA's Webb Helped Rule Out Asteroid's Chance of 2032 Lunar Impact — NASA Science · Webb blog.
science.nasa.gov · primary
Asteroid 2024 YR4 Facts — NASA Science.
science.nasa.gov · primary
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