Of all the asteroids that threaten the planet, 2024 YR4 is unique. Soon after it was spotted in December 2024, telescopic observations around the world immediately established it as The most dangerous space rock ever discovered-which had a 3.1-percent (or 1 in 32) chance of hitting Earth on December 22, 2032. one of the cities Potentially on its way, this 60-meter asteroid would have unleashed the power equivalent of several nuclear bombs, devastating the unfortunate metropolis.
Earth impact was finally ruled out in February last year. But a late plot twist revealed that the chance of 2024 YR4 colliding with our moon on the same date was 4.3 percent (1 in 23). Now, a concerted effort by astronomers indicates that the asteroid will also comfortably miss our alabaster companion by 21,200 kilometers.
Remarkably, this revelation comes from the James Webb Space Telescope (JWST), an observatory that was designed to look at ancient black holes, distant galaxies, twisted stars and far-flung planets – not to help protect the planet from rogue asteroids. Its incredibly perceptive infrared vision, however, was able to track the asteroid in February when it was 450 million kilometers from Earth – a feat no other telescope could accomplish.
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“We think it’s certainly the faintest object ever seen in the solar system,” says andy rivkinAn astronomer and planetary defense researcher at the Johns Hopkins Applied Physics Laboratory in Maryland who led the JWST effort Track 2024 YR4.
“I’m really amazed at what JWST is able to do for us with a real-life, short-term response to an asteroid threat,” says Katherine KumamotoHead of the Planetary Defense Program at Lawrence Livermore National Laboratory in California.
Some may complain that while a 2032 lunar impact would seem harmless, it would be quite explosive. visible to the naked eye—Not in the cards anymore. But there was a real risk that some debris dropped from the Moon would have hit many Earth satellites. If JWST had determined that 2024 YR4 was ripe for a violent encounter with the moon, experts would have had six extremely short years to deal with it. “It’s really nice that we’re not being forced to reduce this asteroid to that time scale,” says Kumamoto.
The NASA-funded Asteroid Terrestrial-impact Late Warning System (ATLAS) telescopic network first discovered 2024 YR4 just after Christmas Day in 2024. Initially, there was nothing to worry about. But additional observations by other observatories show it has a 1 percent chance of hitting Earth in 2032. Those impact probabilities ultimately reached their troubling peak of 3.1 percent in mid-February of 2025.
All scientists concerned were eager to find out whether the probabilities of impact would continue to increase or decrease. But refining the orbit of 2024 YR4 was a daunting task: It was moving rapidly away from Earth, and by May 2025, it would disappear from sight until it returned years later. “We were not expecting to see the object again until the spring of 2028,” says juan luis canoAn aerospace engineer at the European Space Agency’s Near-Earth Object Coordination Centre.
If there was a possibility of a devastating asteroid strike, astronomers would have only four years to prepare. According to planetary defense experts, even eight years were insufficient to prepare a space flight mission that could take away an Earth-bound asteroid.
Astronomers first needed to find out its actual size. Observations with visible light can yield only rough estimates of the space rock’s dimensions. But when viewed in the infrared, the asteroid’s thermal brightness roughly matches its size.
The same month 2024 YR4 was discovered, a study concluded that JWST could be used Hunt small asteroids of interest. So when 2024 YR4 ambushed everyone, Rivkin and his colleagues presented a Proposal Expanding its scope with a $10 billion telescope. It worked wonders: They found that the asteroid was 60 meters wide, making it a comfortable city destroyer.
By May, once the possibility of a collision with Earth had been ruled out, scientists placed the chance of a lunar collision at 4.3 percent. Besides the fact that there will probably be both American and Chinese astronauts on the Moon by 2032, who certainly won’t appreciate being pancaked or sent into space until 2024 YR4, modeling study It was suggested that a shotgun spray of debris could knock many of Earth’s communications satellites out of the sky. “This would have potentially global consequences,” says Rivkin.
This prompted the Planet Defenders to outline a plan to prevent lunar impacts, which they described in an article arXiv preprint. “In the event that an impact was demonstrated to pose a substantial threat to space assets, there is a reasonable possibility that we would have tried to do something to prevent the asteroid from colliding,” Kumamoto says. But “you can’t really avoid it” in the time left. This left three options: hit the spacecraft to break the rock into smaller pieces, vaporize it with a spacecraft equipped with a nuclear device, or let the impact occur.
“When we saw that it might hit the Moon, we wanted to follow it,” says Rivkin. “JWST was the only facility that could do this before 2028.” They had a small window of opportunity for two observations in February when 2024 YR4 would be close to several background stars whose positions astronomers knew with high confidence; This will allow them to monitor the asteroid’s movements with great precision.
During JWST’s observations, “the asteroid was four billion times fainter than the human eye can see,” says julian de wittA planetary scientist at the Massachusetts Institute of Technology and member of Rivkin’s team. And yet it worked. Next, NASA’s Near-Earth Object Study Center In Southern California and the European Space Agency Near-Earth Object Coordination Center Observations in Italy were used to recalculate the orbit of 2024 YR4. outcome? The moon was also safe from harm.
2024 YR4 will no longer be a threat. but NASA’s Near Earth Object Surveyor The space observatory (launching in 2027) and the soon-to-be-operational Vera C. Rubin Observatory in Chile are set to find hundreds of thousands of potentially hazardous asteroids over the next few years. It’s welcome news that JWST can help protect not only the Earth, but the Moon as well.
“We are prepared to face any future threats,” says Cano. “And they will come.”
