For a moment, it seemed possible that asteroid 2024YR4 would hit Earth in 2032. As its probability of impact climbs to a record-breaking 3 percent, astronomers are scrambling to refine its trajectory using some of the most powerful telescopes on Earth. However, just when people's concerns about it were at their peak, new observations overturned people's ideas-its risk was reduced to almost zero.

Image of asteroid 2024 YR4 taken by the European Southern Observatory's Very Large Telescope (VLT). Shown in the figure is the trajectory of the asteroid in the night sky in January 2025, which was observed in the infrared band with the HAWK-I instrument. These early observational data raise the probability of an asteroid impact on December 22, 2032 to more than 1%. However, thanks to newer data, that chance has dropped to almost zero. Photo credit: ESO/O. Heinault

The latest observations from the European Southern Observatory's Very Large Telescope (ESO's VLT) and other facilities around the world have all but ruled out the possibility of a collision with Earth for asteroid 2024 YR4. Scientists have tracked the asteroid closely over the past few months as its estimated probability of impact in 2032 climbed to 3 percent - the highest probability ever recorded for a sizable asteroid. However, new data has reduced this risk to almost zero.

2024YR4 is estimated to be between 40 and 90 meters in diameter and was discovered at the end of December. Preliminary calculations show that it is likely to collide with Earth on December 22, 2032. Due to its size and initial risk level, the asteroid quickly became a top concern on the European Space Agency's (ESA) risk list, which tracks space objects with the potential to impact Earth.

Evolution of the 2024YR4 asteroid risk corridor using observational data up to February 20, 2025. Each red dot represents the asteroid's likely location on December 22, 2032. Yellow dots represent locations that best fit existing observational data. Click here to see the sequence of events and more details in this video. Image credit: ESA/Planetary Defense Office Precise tracking using the European Southern Observatory’s VLT

In mid-January, ESO's VLT observed 2024YR4, providing astronomers with key data needed to more precisely calculate its orbit. Combined with data from other observatories, the VLT's very precise measurements improve our understanding of the asteroid's orbit, bringing the probability of impact to over 1% - a key threshold that triggers hazard mitigation. More observations were triggered, and the International Asteroid Warning Network issued a notification of a potential asteroid impact, alerting planetary defense groups, including the Space Mission Planning Advisory Group, to a possible impact.

As the asteroid was observed by multiple telescopes around the world and astronomers modeled its orbit, the impact probability rose to about 3% on February 18, which is the highest impact probability recorded so far for an asteroid larger than 30 meters. However, the very next day, new observations from the European Southern Observatory's VLT reduced the risk of impact by half.

The image shows the orbit of asteroid 2024YR24, shown in red as it approached Earth on December 22, 2032. Thanks to recent data, including from the European Southern Observatory's Very Large Telescope, the likelihood of an impact with Earth is extremely slim. The sizes of the planets here are not drawn to scale; their dimensions have been exaggerated for clarity. Image source: ESA

The rise and fall in asteroid impact probability follows an expected and known pattern. To know where the asteroid will be in 2032, astronomers need to extrapolate from a fraction of the orbits measured so far. Olivier Hainaut, an astronomer at the European Southern Observatory, made an analogy: "Because of the uncertainty, the orbit of the asteroid is like the beam of a flashlight: getting wider, getting farther, and getting blurrier. As we observe more, the beam becomes sharper and narrower. The Earth is getting brighter and brighter by this beam of light: the possibility of an impact increases."

This is a series of observations made by the European Southern Observatory's Very Large Telescope in January 2025, shortly after the near-Earth asteroid 2024YR4 was discovered in December 2024. The images are aligned so that the asteroid is fixed in the center of the frame, while the stars in the background appear to be moving.

The new VLT observations, along with data from other observatories, allow astronomers to place enough constraints on the orbit to all but rule out an impact with Earth in 2032. "The narrower beam is now moving away from Earth. At the time of writing, ESA's Near-Earth Object Coordination Center reports an impact probability of about 0.001 percent, and the asteroid is no longer at the top of ESA's risk list," Heinault said.

As the asteroid 2024 YR4 moves away from Earth, it becomes increasingly dimmer, making it difficult for all but the largest telescopes to detect it. The European Southern Observatory's VLT played an important role in the observation of this asteroid due to its mirror size and ultra-high sensitivity, as well as the excellent dark skies of the European Southern Observatory's Paranal Observatory in Chile, where the telescope is located. This makes it ideal for tracking dark objects like 2024YR4 and other potentially hazardous asteroids.

This is a series of observations made by the European Southern Observatory's Very Large Telescope in January 2025, shortly after the near-Earth asteroid 2024YR4 was discovered in December 2024. Asteroids are dark sources that move diagonally against a background of fixed stars.

Unfortunately, the very pristine dark skies of Paranal that make these important measurements possible are currently under threat from the INNA industrial megaproject of AES Andes, a subsidiary of US power company AES Corporation. According to the plan, the project covers an area similar to that of a small city, and is about 11 kilometers away from the VLT. Due to its size and distance, INNA will have a devastating impact on Paranal's sky quality, particularly due to light pollution caused by its industrial facilities. As the sky becomes brighter, telescopes like the VLT will lose the ability to detect some of the faintest cosmic targets.

"With brighter skies, the VLT will lose dim 2024YR4 about a month earlier, which will have a huge impact on our ability to predict impacts and prepare mitigation measures to protect the Earth," Hanaut warned.

The observations were obtained in the context of ESA and the European Southern Observatory's collaborative contribution to the International Asteroid Warning Network. The observation team consists of Olivier R. Hainaut (ESA), Marco Micheli (ESA Coordination Center for Near-Earth Objects), Bruno Leibundgut (ESA), Andrew Williams (former ESA, now ESA), Detlef Koschny (Technical University of Munich, Germany), and Luca Conversi (ESA). Maxime Devogele (ESA), Julia de Leon (Canary Institute of Astronomy, Spain) and Nicholas Moskovitz (Lowell Observatory, USA) also joined the observation of 2024YR4. The VLT instruments used were FORS2 and HAWK-I.

Compiled from /ScitechDaily