Why NASA keeps changing the probability of an asteroid impacting Earth in 2032

• On Feb. 18, 2025, NASA updated the probability of asteroid “2024 YR4” impacting Earth on Dec. 22, 2032, from 2.6% to 3.1%. The European Space Agency (ESA) also updated its estimate of the probability of Earth impact to 2.8%, adding that for an asteroid of its size, it “now holds the record for the highest impact probability reached.”

• News media outlets published headlines placing 2024 YR4 in a “city killer” category of asteroids — terminology not used by NASA or ESA officials to describe the object. Social media users also shared the news without including any contextual information.

• However, by Feb. 19, just one day later, NASA decreased 2024 YR4’s impact probability from 3.1% to 1.5%. NASA and the ESA both reported the asteroid “has a very small chance” of impacting Earth.

• The ESA further explained the chance of impact “is likely to fall to zero,” and that the process of establishing multiple data points for an asteroid’s path “will often appear risky during initial observations, get riskier and then suddenly become entirely safe.”

• Further, a 2024 report authored by NASA and other agencies recalled a separate incident from 2023 in which the ESA dealt with disinformation and misinformation efforts by “malicious actors who used targeted terms and hashtags like ‘city killer’ and ‘#citykiller’ to alarm the public” — the same terms some news media outlets used in their headlines about 2024 YR4.

On Feb. 18, 2025, the Center for Near Earth Object Studies, a facility within the scope of NASA’s Jet Propulsion Laboratory (JPL), updated the probability of the asteroid named 2024 YR4 impacting Earth on Dec. 22, 2032, from 2.6% to 3.1%.

On the same day, the European Space Agency (ESA) updated its own estimate of that probability to 2.8%. The ESA reported, “For asteroids larger than 30 meters [or 98 feet] in size, 2024 YR4 now holds the record for the highest impact probability reached, and the longest time spent with an impact probability greater than 1%.”

After the agencies’ updates, news media outlets published headlines about the object falling into a “city killer” category of asteroids. Social media users also shared the news without including any context. For example, a Reddit user shared an image graphic displaying an illustration of a massive object striking Earth, with the caption, “NASA says there’s now a 3.1% chance that asteroid 2024 YR4 will hit Earth in 2032.” The user added the caption, “Day by day probability is increasing.”

Just one day later, on Feb. 19, after all of the “city killer” news headlines and context-free memes, NASA decreased the probability of the asteroid impacting Earth to 1.5%, the same as a 98.5% chance of no impact.

NASA and the ESA both reported that 2024 YR4 — measuring about 130 to 300 feet (or 40 to 90 meters) wide — “has a very small chance” of impacting Earth in 2032. The ESA further published the chance of impact “is likely to fall to zero,” explaining in a 2022 video that the process of establishing multiple data points for an asteroid’s path “will often appear risky during initial observations, get riskier and then suddenly become entirely safe.”

“As more data are being acquired daily, the impact probability is subject to frequent change,” the ESA said. “As we obtain more observations of the object, the impact probability is very likely to grow and then, suddenly, go to zero if the object is not on an impact trajectory with the Earth.”

The Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Rio Hurtado, Chile, first discovered 2024 YR4 on Dec. 27, 2024. NASA did not respond to a request for comment.

‘City killer’ terminology ‘to alarm the public’

Numerous news media outlets published the words “city killer” in their article headlines to describe the size of the 2024 YR4 asteroid. However, those stories lacked any direct quotes from NASA officials using that phrase to describe 2024 YR4. While a very few old pages on the NASA website displayed outdated documents with the words “city killer,” the agency’s website did not directly reference 2024 YR4 with the same terminology.

In a 2024 report concerning “preparedness and response challenges associated with the threat of asteroid impact,” authored by NASA’s Planetary Defense Coordination Office (PDCO) and other agencies, the authors recalled an experience that casts the “city killer” terminology in a negative light.

On page A-21 — a page concentrating on instances of misinformation and disinformation regarding the potential of asteroid impact — the report read, “ESA reiterated an experience they had in 2023 when a small delay in correcting inaccurate information was picked up by malicious actors who used targeted terms and hashtags like ‘city killer’ and ‘#citykiller’ to alarm the public. ESA was able to publish the real information, explained the delay and aggressively tamped down the activity until it subsided.”

What to know about 2024 YR4 possibly impacting Earth

The ESA and NASA both published special fact sheets for asteroid 2024 YR4. For example, the fact sheets featured data about the object’s estimated velocity, consequences of potential impact and location of where the asteroid might impact.

Regarding the “very small chance” of Earth impact, the ESA noted, “There is no concept such as a ‘constant speed’ at which the object moves towards the Earth (there is a complicated relative motion between the two objects at any moment in time). However, we can be certain that the velocity when the object approaches Earth in December 2032 will be about 17.3 km/s which is equivalent to 62,500 km/h.” The figures convert to about 10.7 miles per second and 40,389 miles per hour.

A young man on a road watching the Milky Way and lighting the road with a flash, in A Veiga, Ourense, Spain. (Image courtesy of Carlos Fernandez/Getty Images)

The ESA further reported it had not yet assessed in detail the consequences of impact. “If the asteroid is found to have a diameter in the 50 meters range, and if it can be confirmed that it is a rocky asteroid, the effects would be similar to those of the Tunguska impact in 1908, where a surface area of 2000 square kilometers [or 772 square miles] was devastated and 20 million trees were affected. This is equivalent to the area of a circle 25 kilometers [or 16 miles] in diameter. If larger, the effects would extend to several tens of kilometers.”

Britannica.com published of the Tunguska event in 1908, in which scientists believe either an asteroid or comet impacted Siberia after first exploding in the atmosphere, “The energy of the explosion is estimated to have been equivalent to the explosive force of as much as 15 megatons of TNT — a thousand times more powerful than the atomic bomb dropped on Hiroshima, Japan, on August 6, 1945.”

Regarding a location of potential impact, NASA reported, “In the unlikely event that 2024 YR4 is on an impact trajectory, the impact would occur somewhere along a risk corridor which extends across the eastern Pacific Ocean, northern South America, the Atlantic Ocean, Africa, the Arabian Sea and South Asia.”

One question in the ESA fact sheet asked, “Could a new planetary defence mission be developed in time to go to and deflect this asteroid? Or could an existing mission be diverted to do so?” The answer, mentioning the Space Mission Planning Advisory Group (SMPAG), read, “Just this sort of assessment will be done by SMPAG as soon as it is activated. At this moment it is too soon to propose any such action. However, it is already clear that 8 years to the impact is very tight.”

NASA reported the asteroid’s probability chances for Earth impact decreased significantly for the future years of 2039, 2043, 2047, 2063, 2067 and 2079. For example, NASA identified the next highest probability figure beyond 2032 as a 0.00033% chance of Earth impact on Dec. 23, 2039.

James Webb Space Telescope and loss of visibility

The ESA announced astronomers intend on utilizing the James Webb Space Telescope to study 2024 YR4, noting they will lose visibility of the asteroid “in the next couple of months due to its orbital properties.”

They added, “If an impact probability cannot be completely ruled out by around April 2025, most likely, we will not be able to remove the object from the ESA Risk List until the asteroid becomes observable again from June 2028.”

Sources:

“2024 YR4 – NASA Science.” NASA, 7 Feb. 2025, https://science.nasa.gov/solar-system/asteroids/2024-yr4/.

“Asteroid 2024 YR4 Reaches Level 3 on the Torino Scale.” NASA Jet Propulsion Laboratory, Center for Near Earth Object Studies, 31 Jan. 2025, https://cneos.jpl.nasa.gov/news/news210.html.

“Asteroid Watch.” NASA Jet Propulsion Laboratory (JPL), https://www.jpl.nasa.gov/asteroid-watch/.

“Asteroids.” NEO, Near-earth objects coordination centre, https://neo.ssa.esa.int/search-for-asteroids.

@AsteroidWatch. “NASA Asteroid Watch.” X, https://x.com/AsteroidWatch.

“FAQ Asteroid 2024 YR4.” European Space Agency (ESA), ESA Communication Dept. and ESA Planetary Defence Office, 12 Feb. 2025, https://esamultimedia.esa.int/docs/spacesafety/NEO/media/asteroid2024yr4_faq_ESA.pdf.

“How Asteroids Go from Threat to No Sweat.” YouTube, European Space Agency, ESA, 24 Feb. 2022, https://www.youtube.com/watch?v=3_6Ff_2eBAk.

Molly L. Wasser. “NASA Continues to Monitor Orbit of Near-Earth Asteroid 2024 YR4.” NASA, Planetary Defense, 7 Feb. 2025, https://blogs.nasa.gov/planetarydefense/2025/02/07/nasa-continues-to-monitor-orbit-of-near-earth-asteroid-2024-yr4/.

Reber, Josh. “2024 YR4 Surpasses Apophis as ‘Riskiest’ Asteroid Ever Detected – Rocket Science.” European Space Agency (ESA), 19 Feb. 2025, https://blogs.esa.int/rocketscience/2025/02/19/2024-yr4-surpasses-apophis-as-riskiest-asteroid-ever-detected/.

—. “Asteroid 2024 YR4 – Latest Updates – Rocket Science.” European Space Agency (ESA), 4 Feb. 2025, https://blogs.esa.int/rocketscience/2025/02/04/asteroid-2024-yr4-latest-updates/.

—. “James Webb Space Telescope Will Study Asteroid 2024 YR4 – Rocket Science.” European Space Agency (ESA), 10 Feb. 2025, https://blogs.esa.int/rocketscience/2025/02/10/james-webb-space-telescope-will-study-asteroid-2024-yr4/.

“Sentry: Earth Impact Monitoring.” NASA Jet Propulsion Laboratory, Center for Near Earth Object Studies, https://cneos.jpl.nasa.gov/sentry/details.html#?des=2024%20YR4.

Strickland, Ashley. “An Asteroid’s Chances of Hitting Earth Keep Shifting. Here’s Why That Is Happening.” CNN, 19 Feb. 2025, https://www.cnn.com/2025/02/19/science/asteroid-2024-yr4-earth-collision-risk/index.html.

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