The Gemini South telescope in Chile has enabled astronomers to construct a 3D representation of the asteroid that has a slim chance of colliding with our Moon.
Observations with the telescope revealed more about what type of asteroid it is, including how fast it's spinning and how big it is, as well as the possibility it was nudged towards Earth by Jupiter.
Asteroid 2024 YR4 was detected on 27 December 2024 by the Asteroid Terrestrial-impact Last Alert System (ATLAS).
It's currently moving away from Earth, but eventually its orbit will bring it back in this direction.
Initially, data showed there was a chance – albeit slim – that 2024 YR4 could hit Earth in December 2032.
The chances of that happening have now fallen to practically zero, scientists say, but now it seems there's a chance – again, a slim one – that 2024 YR4 could hit our Moon.
Gemini South looks at 2024 YR4
The Gemini South telescope is part of the International Gemini Observatory, operated by NSF NOIRLab.
Astronomers used Gemini South to carry out investigations of asteroid 2024 YR4 on 7 February 2025.
The team, led by Bryce Bolin of Eureka Scientific, were able to to capture images of the near-Earth asteroid in different wavelengths of light.
This included examining its 'light curve', which is a line graph produced by plotting how an object's light output changes over time.
They were able to determine asteroid 2024 YR4's composition, orbital characteristics and make a 3D map showing its true shape.
"Our observations with Gemini South provided a crucial piece of the puzzle in determining 2024 YR4’s characteristics," says Bolin, lead author of the paper in The Astrophysical Journal Letters.
"Studying this asteroid was vitally important in understanding the population of Earth crossers that have the potential to be Earth impactors and are poorly understood."
International Gemini Observatory/NOIRLab/NSF/AURA/M. Zamani
Uncovering the secrets of 2024 YR4
2024 YR4 is likely an S-type asteroid, say the team, which means it has a composition rich in silicates.
The light curve has revealed it's about 30–65 metres in diameter, making it one of the largest objects in recent history that could impact the Moon.
The team say that, while it's incredibly likely the asteroid will miss the Moon entirely, if 2024 YR4 did smash into the Moon, it would be an opportunity to study the sort of impact crater left by an object whose size and shape are well known.
Other results from the Gemini South observations include the revelation that asteroid 2024 YR4 is a sort of 'hockey puck' shape and that it makes one rotation every 20 minutes.
"This find was rather unexpected since most asteroids are thought to be shaped like potatoes or toy tops rather than flat disks," says Bolin.
Asteroid origins
The Gemini South observations of asteroid 2024 YR4 also enabled the team to work out where it came from and how it's wandered so close to Earth's orbital path.
It most likely originated from the main asteroid belt, the team say, and may have been pushed towards Earth by the gravitational influence of Jupiter.
Asteroid 2024 YR4 is also spinning backwards, or in a 'retrograde' direction, which, say the team, suggests it could have migrated inward from the central Main Belt region.
"We are a bit surprised about its origin in the central main asteroid belt, which is a location in the asteroid belt that we did not think many Earth-crossing asteroids could originate from," says Bolin.
"Understanding the properties and origins of near-Earth asteroids is proving critical for understanding the risk of collisions between our planet and major bodies in crossing orbits," says Martin Still, NSF program director for the International Gemini Observatory.
"The Gemini telescopes and other astronomical observatories are vital tools for planetary defence."
Read the full paper at arxiv.org/abs/2503.05694
