Press Release

ESO observations help almost fully rule out 2024 YR4 asteroid impact

25 February 2025

New observations of 2024 YR4 conducted with the European Southern Observatory’s Very Large Telescope (ESO’s VLT) and facilities around the world have all but ruled out an impact of the asteroid with our planet. The asteroid has been closely monitored in the past couple of months as its odds of impacting Earth in 2032 rose to around 3%, the highest impact probability ever reached for a sizable asteroid. After the latest observations, the odds of impact dropped to nearly zero.

The asteroid 2024 YR4, estimated to be about 40 to 90 metres in diameter, was discovered in late December last year on an orbit that could cause it to collide with Earth on 22 December 2032. Because of its size and likelihood of impact, the asteroid quickly rose to the top of the European Space Agency’s (ESA) risk list, a catalogue of all space rocks with any chance of impacting Earth.  

ESO’s VLT was used to observe 2024 YR4 in mid-January, giving astronomers the crucial data they needed to more precisely calculate its orbit. Combined with data from other observatories, the very precise measurements from the VLT improved our knowledge of the asteroid's orbit, leading to an impact probability exceeding 1% — a key threshold to trigger disaster mitigation. More observations were triggered and the International Asteroid Warning Network issued a potential asteroid impact notification, alerting planetary defence groups, including the Space Mission Planning Advisory Group, about the possible impact.

With multiple telescopes around the world observing the asteroid, and astronomers modelling its orbit, the impact probability rose to around 3% on 18 February, the highest impact probability ever recorded for an asteroid larger than 30 metres. However, just the next day, new observations made with ESO’s VLT cut the impact risk in half.

This rise and fall of the asteroid’s impact probability follows an expected and understood pattern. To know where the asteroid will be in 2032, astronomers extrapolate from the small bit of the orbit measured thus far. ESO Astronomer Olivier Hainaut makes an analogy: “Because of the uncertainties, the orbit of the asteroid is like the beam of a flashlight: getting broader and broader and fuzzier in the distance. As we observe more, the beam becomes sharper and narrower. Earth was getting more illuminated by this beam: the probability of impact increased.”

The new VLT observations, together with data from other observatories, have allowed astronomers to constrain the orbit enough to all but rule out an impact with Earth in 2032. “The narrower beam is now moving away from Earth,” Hainaut says. At the time of writing, the impact probability reported by ESA’s Near-Earth Objects Coordination Centre is around 0.001% and the asteroid no longer tops ESA’s risk list.

As 2024 YR4 is moving away from Earth, it has become increasingly faint and difficult to observe it with all but the largest telescopes. ESO’s VLT has been instrumental in observations of this asteroid because of its mirror size and superb sensitivity, as well as the excellent dark skies at ESO’s Paranal Observatory in Chile, where the telescope is located. This makes it ideal to track faint objects such as 2024 YR4 and other potentially dangerous asteroids. 

Unfortunately, the same Paranal's pristine dark skies that made these crucial measurements possible are currently under threat by the industrial megaproject INNA by AES Andes, a subsidiary of the US power company AES Corporation. The project is planned to cover an area similar in size to that of a small city and be located, at the closest point, about 11 km from the VLT. Due to its size and proximity, INNA would have devastating effects on the quality of the skies at Paranal, especially due to light pollution from its industrial facilities. With a brighter sky, telescopes like the VLT will lose their ability to detect some of the faintest cosmic targets.

Hainaut warns: “With that brighter sky, the VLT would lose the faint 2024 YR4 about one month earlier, which would make a huge difference in our capability to predict an impact, and prepare mitigation measures to protect Earth”.

More information

The observations were obtained in the context of the collaboration between ESA and ESO in contribution to the International Asteroid Warning Network. The team is composed of Olivier R. Hainaut (ESO), Marco Micheli (ESA NEO Coordination Centre), Bruno  Leibundgut (ESO), Andrew Williams (formerly ESO, now ESA), Detlef Koschny (Technical University Munich, Germany), Luca Conversi (ESA). For the 2024 YR4 observations, they were joined by Maxime Devogele (ESA), Julia de Leon (Instituto de Astrofisica de Canarias, Spain) and Nicholas Moskovitz (Lowell Observatory, United States). FORS2 and HAWK-I were the VLT instruments used.

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration for astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, Czechia, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates ALMA on Chajnantor, a facility that observes the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society. 

Links

• ESA latest updates on 2024 YR4 
• Photos of the VLT
• For journalists: subscribe to receive our releases under embargo in your language and apply to take part in ESO's (partly funded) 2025 strategic media visit (NEW)
• For scientists: got a story? Pitch your research 
• World's darkest and clearest skies at risk from industrial megaproject

Contacts

Olivier Hainaut
ESO Astronomer
Garching bei München, Germany
Tel: +49 89 3200 6754
Cell: +49 151 2262 0554
Email: ohainaut@eso.org

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: press@eso.org

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