08-04-2025
Hawaiʻi telescopes spot asteroid that could slam into the Moon: 8 things to know
HONOLULUJ (KHON2) — Astronomers at W. M. Keck Observatory on Maunakea have uncovered new insights about 2024 YR4. This is an Earth-crossing asteroid first spotted in December 2024.
Their findings provide a closer look at the asteroid's composition and characteristics as well as revealing a surprising origin.
YR4, a rocky and solid object, likely hails from an asteroid family in the central Main Belt. It's a region traditionally not known for producing Earth-crossing asteroids.
'This asteroid is a solid, stony type that rotates in a retrograde direction and has a flattened, irregular shape,' said Bryce Bolin, a research scientist with Eureka Scientific and lead author of the study. 'These physical properties are critical in determining how we might deflect the asteroid if it ever poses a threat to Earth.'
While the asteroid made headlines with initial concerns about a potential Earth impact in 2032, further observations have since ruled out a collision with Earth.
However, the asteroid may still have a ~2% chance of striking the Moon instead. This scenario has the potential to provide a rare opportunity for scientists to study the crater it would create.
This is what we know:
While 2024 YR4 was once feared to impact Earth in 2032, updated calculations show it is unlikely to collide with our planet.
However, the asteroid could strike the Moon instead. It would offer scientists a unique chance to study how the size of an asteroid correlates with the crater it forms.
'If it does [hit the Moon], it would give scientists a rare chance to study how the size of an asteroid relates to the size of the crater it creates—something we haven't been able to measure directly before,' explained Bryce Bolin, a research scientist with Eureka Scientific and the lead author of the study on asteroid 2024 YR4.
Unlike many Earth-crossing asteroids that come from the outer parts of the solar system, YR4's origins lie within the Main Belt between Mars and Jupiter.
This is a region traditionally not associated with objects that cross Earth's orbit.
'YR4 is a solid, stony type that likely originated from an asteroid family in the central Main Belt between Mars and Jupiter, a region not previously known to produce Earth-crossing asteroids,' said around 50-60 meters (160-197 feet) in diameter, YR4 is one of the largest asteroids in recent history to possibly impact the Moon.
Its shape and density suggest it may have been a boulder from a larger rubble-pile asteroid that broke apart.
'YR4 spins once every 20 minutes, rotates in a retrograde direction, has a flattened, irregular shape and is the density of solid rock,' said Bolin. 'At about 50–60 meters in diameter [similar to the width of a football field], it's one of the largest objects in recent history that could hit the Moon.'
Using the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) at Keck Observatory, astronomers were able to analyze YR4 in the infrared spectrum.
This method revealed key properties of the asteroid that would have been invisible to other telescopes.
'We were able to observe YR4 in the infrared, seeing properties of the asteroid that would otherwise be impossible to observe,' added Bolin.
The observation of YR4 was a stroke of luck. Initially intended for studying distant objects beyond Neptune, the team's telescope pivoted due to technical difficulties. This allowed them to collect crucial data on the asteroid's physical properties.
'It was a serendipitous set of circumstances that allowed us to do these observations. The object's orbit was so well determined we knew its position to within less than an arcsecond,' explained Bolin. 'It was moving less than 10 arcseconds per minute… but we got it on our first try. My original science case was imaging for trans-Neptunian objects, but due to technical difficulties, we were able to pivot at the last minute to image the object.'
Asteroids like YR4 often spark curiosity because of their unpredictable paths and potential hazards. YR4's trajectory and size make it an intriguing subject of study, particularly because it lies at the crossroads of several important asteroid families.
Unlike larger asteroids, which are often 'rubble piles' composed of broken-up fragments from larger objects, YR4 appears to be a solid chunk of rock. This is significant, as the shape and structure of an asteroid can affect how it might be deflected if it were to pose a threat to Earth.
The team used data from multiple observatories, including the Gemini South telescope in Chile, and the Asteroid Terrestrial-impact Last Alert System (ATLAS), developed by the University of Hawaiʻi and funded by NASA.
However, it was the high-precision instruments at Keck Observatory that allowed the astronomers to precisely track YR4's position with incredible accuracy.
'The orbit was so well-determined that we knew its position to within less than an arcsecond,' said Bolin. 'If we were off by even a small fraction, we would have missed it.'
Maunakea is home to some of the most advanced telescopes on the planet. The W. M. Keck Observatory's twin 10-meter telescopes are equipped with cutting-edge technology, including high-resolution spectrographs and laser guide star adaptive optics systems.
This power makes it one of the most productive observatories in the world.
The observatory's ability to provide high-precision measurements is invaluable when studying fast-moving objects like YR4. The information gathered from these observations could be crucial in developing rapid response plans should a threatening asteroid be discovered in the future.
While YR4's near miss with Earth doesn't pose a current threat, its study provides important lessons on how scientists track and assess potential asteroid threats.
As astronomers continue to refine their methods of detecting and characterizing asteroids, the data collected from YR4 will serve as a valuable case study for future planetary defense efforts.
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For now, astronomers are keeping a close eye on this Earth-crossing asteroid, and future observations may continue to reveal more about the potential hazards, and opportunities, that asteroids like YR4
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