The global race to find out if asteroid 2024 YR4 will hit Earth

The international scientific community is working against the clock to gather observations of asteroid 2024 YR4, which currently has a probability of more than 2% of impacting the Earth on December 22, 2032.

At the moment, the asteroid is moving further away from Earth as it orbits the Sun, which it completes every four years. With each passing day, it becomes more difficult to observe with Earth-based telescopes. Currently, a telescope with a diameter of at least two meters is required to spot it. By early March, only four-meter telescopes will have the capability to detect it. By April, only the largest observatories on the planet, such as the eight-meter Very Large Telescope in Chile and the 10-meter Gran Telescopio de Canarias (GTC), will be able to reach it.

The final observation opportunity this year will come via the James Webb Space Telescope, which orbits Earth at the second Lagrange point, 1.5 million kilometers away. If all goes well, its detectors may be able to track 2024 YR4 until early May. If these observations don’t rule out the possibility of a potential impact, we’ll need to wait for the body to complete another orbit and approach Earth again in April 2028.

The asteroid’s orbit changes with each revolution around the Sun, due to the gravitational pull of planets and other celestial bodies it encounters. If a potential impact in 2032 is ruled out, the likelihood of a collision in future encounters will significantly decrease.

To date, the International Astronomical Union’s Minor Planet Center has received over 340 observations of this asteroid from telescopes around the world, with each providing its exact position in the sky. Based on these measurements, the European and U.S. space agencies have estimated where the object will be at its closest approach to Earth in December 2032, though this estimation comes with some uncertainty. Since daily calculations began, the chances of a collision have risen, and they now exceed 2%.

“It is very possible that the probability of impact will still increase in the coming days or weeks, until it reaches a point where it falls to zero, because Earth will have been outside the zone of uncertainty,” explains Juan Luis Cano, coordinator of the Information Service of the Planetary Defense Office of the European Space Agency (ESA). This would be similar to what happened with Apophis, a rock that reached a 3% chance of impact and whose collision was ruled out shortly after.

“The opposite option — where the possibility of impact increases as uncertainty decreases, and the probabilities reach 100% — is much more unlikely. We have to continue gathering observations, but as of today, we still have almost a 98% chance of no impact,” says Cano. The engineer provides another crucial piece of information: the probability of being able to rule out an impact with Earth before we lose sight of the asteroid in May is 90%.

The asteroid 2024 YR4 was first discovered on December 27, 2024, by a telescope in Chile. However, due to the holiday season and limited observing time on telescopes, the international community didn’t fully focus on the object until mid-January. By the end of that month, impact risk estimates had already reached 1.3%. As more observations have been collected, that percentage has steadily increased.

The size of 2024 YR4 remains uncertain, and determining it is critical. At present, estimates suggest a range between 40 and 90 meters in diameter. “Based on the electromagnetic spectrum we’ve obtained for this object, we suspect it is more likely to fall toward the smaller end of that range,” explains Cano. If it turns out to be under 50 meters and a collision with Earth is imminent, the strategy would be to let it impact and evacuate the population if necessary. To do this, a radius of several dozen miles around the impact zone would be calculated, Cano adds.

“We’re very excited, but not scared at all,” says Julia de León, an astronomer at the Instituto de Astrofísica de Canarias, who has been monitoring the asteroid closely with several telescopes on Tenerife and La Palma. She believes that the chances of a collision will ultimately be ruled out, and if not, a deflection mission could be prepared in time. De León is one of the European and U.S. scientists who have secured observation time with the James Webb Space Telescope in late April to gain further insight into the body’s characteristics, which remain largely uncertain. “If the complete orbit of this asteroid were like an athletics track, which measures 400 meters, right now we only know the first six,” she explains.

This 48-year-old scientist from the Canary Islands has used the Gran Telescopio de Canarias to uncover a crucial detail about the asteroid: its composition. “The results show that it is made of rock and a certain metal content that we are not able to determine,” she says.

Should an impact occur, the asteroid would likely survive its passage through Earth’s atmosphere and strike the ground or the ocean. A similar 50-meter body crashed in what is now Arizona about 50,000 years ago. It created a crater over a mile in diameter and caused an explosion that wiped out all animal life within a 2.5-mile radius. Another possibility is that the asteroid might break up in the atmosphere. In 1908, a similar-sized object exploded above the Tunguska region of central Russia, leveling 770 square miles of forest.

Another key unknown factor is the angle at which the asteroid would impact Earth. If an impact is confirmed, it would occur somewhere along a long corridor that stretches from the eastern Pacific Ocean and northern South America (Colombia and Venezuela), across the Atlantic Ocean, through the Gulf of Guinea in Africa, the Arabian Sea, and southern Asia, reaching India. While this path does pass through populated regions in America, Africa, and Asia, most of it covers the ocean.

The threat posed by 2024 YR4 triggered the activation of the United Nations’ planetary defense bodies for the first time. Two key organizations are involved in managing the situation: the International Asteroid Warning Network, which is tasked with observing and studying the asteroid, and the Space Mission Advisory Group, responsible for proposing potential response options if the probability of an impact exceeds 1%. In a statement released on Wednesday, this advisory group acknowledged that it “has started to discuss activities but considers it is premature to develop specific recommendations for space missions.” These options will be revisited in late April or early May when more data becomes available or if the probability of impact changes significantly, it said.

The potential methods for deflecting an asteroid like 2024 YR4 range from launching an impact probe to using a nuclear explosion to alter its trajectory. Paolo Martino, head of planetary defense missions at the ESA, acknowledges the technological challenges posed by 2024 YR4: “Predicting the orbit of asteroids of this size is very difficult because they are influenced by many perturbations. This requires extensive study,” he tells EL PAÍS. “Right now, thousands of astrophysicists around the world are working on it.”

When it comes to possible deflection missions, Martino explains that due to is trajectory, launching a study probe to dock with the asteroid would be “very, very complicated.” A more feasible approach would be to launch an impact probe. “Imagine that you are in front of a truck that is going to pass by you,” he explains. “Docking would be equivalent to jumping inside it and surviving. To impact it, you would only have to get in front of it, which is much more painful, but also easier.”

This approach would build on lessons learned from NASA’s DART mission, which became the first to successfully alter the trajectory of an asteroid in 2022. If it is confirmed in 2028 that 2024 YR4 will indeed impact Earth, there would be a four-year window to design and launch an impact mission, something Martino believes is feasible.

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