JWST snaps first image of asteroid that threatened Earth

2024 Y4 almost certainly won't hit us, but there's still a slight chance of a lunar impact. The post JWST snaps first image of asteroid that threatened Earth appeared first on Popular Science.

Apr 3, 2025 - 15:38

JWST snaps first image of asteroid that threatened Earth

The deep space asteroid that recently made headlines for its potential to collide with Earth received its own photoshoot courtesy of NASA’s James Webb Space Telescope. While the images released on April 2 by the European Space Agency provide a faint glimpse at the sizable meteor, the pictures also mark a significant milestone for the most powerful space observatory ever launched into orbit.

The asteroid 2024 YR4 caused a stir earlier this year when astronomers announced there was a not-zero chance of it striking Earth in 2032. Although experts calculated the probability of a catastrophic planetary impact at around 3 percent, the revised estimate now stands at roughly 0.0017 percent—all but guaranteeing the space rock will harmlessly pass us by in a few years. Prior to receiving the all clear, NASA’s James Webb Space Telescope aimed its camera array towards the meteor for a closer inspection of its size, thermal properties, and other details.

A collage of three images showing the black expanse of space. Two-thirds of the collage is taken up by the black background sprinkled with small, blurry galaxies in orange, blue, and white. There are two images in a column at the right side of the collage. On the right side of the main image, not far from the top, a very faint dot is outlined with a white square. At the right, there are two zoomed in views of this area. The top box is labeled NIRCam and shows a fuzzy dot at the center of the inset. The bottom box is labeled MIRI and shows a fuzzy pinkish dot. — This image shows Webb’s recent observation of the asteroid 2024 YR4 using both its NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument). Data from NIRCam shows reflected light, while the MIRI observations show thermal light. On 8 March 2025, the NASA/ESA/CSA James Webb Space Telescope turned its watchful eye toward asteroid 2024 YR4, which we now know poses no significant threat to Earth in 2032 and beyond. This is the smallest object targeted by Webb to date, and one of the smallest objects to have its size directly measured. Observations were taken to study the thermal properties of 2024 YR4, including how quickly it heats up and cools down and how hot it is at its current distance from the Sun. These measurements indicate that this asteroid does not share properties observed in larger asteroids. This is likely a combination of its fast spin and lack of fine-grained sand on its surface. Further research is needed, however this is considered consistent with a surface dominated by rocks that are roughly fist-sized or larger. Webb’s observations indicate that the asteroid measures roughly 60 meters (comparable to the height of a 15-story building). The new observations from Webb not only provide unique information about 2024 YR4’s size, but can also complement ground-based observations of the object’s position to help improve our understanding of the object’s orbit and future trajectory. Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process. NASA, ESA, CSA, STScI, A Rivkin (JHU APL)

2024 YR4 may not make catastrophic history, but it did set a new record for the JWST as the smallest object ever targeted by the telescope. It’s also one of the smallest space objects to have its size directly measured.

But that doesn’t mean 2024 YR4 is tiny by everyday metrics. Earlier estimates put the asteroid somewhere between 130-328 feet in diameter, and after examining the JWST’s images, astronomers now believe it to be around 180-feet-wide, or about the height of a 15-story building. Further analysis indicates 2024 YR4 doesn’t share some of the attributes of larger asteroids, likely due to its fast spin and lack of fine-grained surface sand. Although further research is required, this assessment aligns with what experts know of asteroid surfaces covered fist-sized or larger rocks.

“The new observations from Webb not only provide unique information about 2024 YR4’s size, but can also complement ground-based observations of the object’s position to help improve our understanding of the object’s orbit and future trajectory,” the ESA explained in its statement.

Astronomers will continue to study 2024 YR4 until it fades from view as its orbital path takes it away from Earth. It’ll be another four years before the asteroid begins its return towards us, at which point more research will be conducted. With any luck, experts will be able to revise their estimate for a 2024 YR4 rendezvous with the moon. Currently, there’s about a 1.7 percent chance of a lunar impact—although that number is also expected to drop over time.

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