For a few tense weeks earlier this year, asteroid 2024 YR4 loomed large in the minds of astronomers and the public alike. Initially thought to pose a potential risk of impact with Earth, the space rock has since been cleared of that danger. Now, the James Webb Space Telescope (JWST) has delivered the most detailed observations of the object to date.
A Brief Scare And A Big Reveal
Discovered in early January 2024, asteroid 2024 YR4 immediately drew attention due to preliminary orbital calculations suggesting a 1-in-83 chance of hitting Earth in 2032 — an impact probability of about 1%.
As expected, follow-up observations steadily refined the asteroid’s trajectory. By late February, the probability of collision dropped to near zero. The threat had passed, but interest in the asteroid endured — not for its danger, but for what it might teach us.
JWST’s Observations Of The Building-sized Rock
In March, scientists turned the JWST’s NIRCam and MIRI instruments toward 2024 YR4, capturing it in both visible and thermal light. The results confirmed that the asteroid is around 200 feet (60 meters) in diameter — “just about the height of a 15-story building,” as described by Andy Rivkin, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory.
These measurements went beyond size. By analyzing how the asteroid absorbs and emits heat, scientists uncovered details about its surface properties and spin rate. According to Rivkin, the asteroid’s thermal behavior “is not like what we see in larger asteroids,” which typically have smoother, more insulating regolith.
Instead, the surface of 2024 YR4 appears rougher and more fragmented: “dominated by rocks that are maybe fist-sized or larger,” Rivkin said. This surface texture affects how heat is absorbed during the day and radiated at night.
How JWST’s‘s View Of 2024 Yr4 Could Shape Future Asteroid Defenses?
The true value of this observation lies in how it may inform the response to future asteroid threats. As Rivkin emphasized, studying near-Earth objects with JWST is “invaluable” for planetary defense.
In short, 2024 YR4 may be harmless, but it’s helping scientists refine their playbook for when a real threat appears. The ability to quickly assess an asteroid’s composition, size, spin, and surface is important for choosing the right mitigation strategy, such as deflection, disruption, or evacuation.
From Scare To Science
The JWST’s first close-up study of a former potential impactor underscores how astronomical panic can evolve into productive research. It also reflects a new era in space observation capabilities, where objects just a few dozen meters wide — the kind that could go unnoticed until it’s too late — are now within the reach of detailed characterization.
“All together, we have a better sense of what this building-sized asteroid is like,” said Rivkin.
With more telescopes coming online and data from missions like NASA’s DART still being processed, the planetary defense community is better equipped than ever to face what the cosmos may throw our way. Asteroids like 2024 YR4 may no longer scare us, but they’re still very much worth watching.
