Lunar Impact? Asteroid 2024 YR4 and the Danger to the Moon

SETI Institute astronomer Dr. Franck Marchis spoke with planetary astronomer Dr. Andy Rivkin of the Johns Hopkins University Applied Physics Laboratory about Asteroid 2024 YR4, a near-Earth object found in late December 2024. Initial observations raised issues when its orbit instructed the small chance of an Earth impression. Continued monitoring now confirms that there isn’t a hazard to Earth, however up to date calculations point out a roughly 4% likelihood that the asteroid might strike the Moon on December 22, 2032.

Discovery and Early Analysis

The asteroid’s provisional designation encodes its discovery date: “2024 Y” alerts objects discovered between December 16 and 31, 2024, and “R4” identifies it because the 117th object found in that point interval. When first detected, astronomers might solely measure a degree of sunshine. Without understanding its albedo, the reflectivity of its floor, they estimated a dimension between 40 and 90 meters. That vary represented something from a darkish, charcoal-like physique to a shiny, extremely reflective rock.

Because early orbital knowledge instructed a possible Earth encounter, observatories worldwide contributed follow-up observations. Probabilities briefly climbed to roughly 3% for an Earth impression earlier than extra measurements dominated that out. Attention then shifted to the Moon, the place a small however non-zero threat stays.

Precision from Space-Based Infrared

To refine each the orbit and dimension of the asteroid, researchers used the James Webb Space Telescope (JWST). Unlike ground-based telescopes, JWST operates exterior Earth’s environment from its location on the Sun–Earth L2 Lagrange level and might seize infrared radiation, which is the warmth emitted by an object somewhat than the daylight it displays. Measuring the asteroid’s thermal emission yields a extra correct measurement of the diameter than early estimations.

JWST measured asteroid 2024 YR4 to be roughly 60 meters in diameter. Telescopes on Earth tracked how shortly it spins—as soon as each 20 minutes—which helped JWST get a gentle brightness studying. Because JWST can watch it longer than Earth-based observatories, it offered a clearer image of the asteroid’s path and the slight likelihood it might hit the Moon.

Potential Lunar Impact

If 2024 YR4 does collide with the Moon, fashions predict:

• Creation of a crater roughly 1 kilometer large on the southern close to facet.
• Ejection of particles into lunar orbit and presumably into Earth’s gravitational affect, creating a short lived meteor bathe.
• Localized hazards for lunar satellites, future crewed bases, and deliberate infrastructure, akin to NASA’s Gateway.

The moon has endured impacts of this scale many instances over geologic historical past, however none have been noticed in actual time with trendy devices. For comparability, similar-sized asteroids are anticipated to strike the Moon as soon as each 4,000–5,000 years.

Scientific Opportunity

A well-monitored impression would provide uncommon knowledge:

• Seismology – New seismometers might probe the Moon’s inside construction and core dimension by recording impact-generated moonquakes
• Surface evolution – Observing contemporary ejecta over time would calibrate fashions of house weathering, the chemical and spectral adjustments attributable to photo voltaic wind and micrometeorite bombardment
• Impact physics – Comparing the incoming asteroid’s measured form, mass, and velocity with the ensuing crater would take a look at present impact-formation fashions, a lot as NASA’s DART mission did on the asteroid Dimorphos.

Composition and Structure

Spectroscopy carried out from ground-based telescopes identifies 2024 YR4 as an S-type asteroid, composed of strange chondrite rock much like the targets of previous missions akin to JAXA’s Hayabusa to Itokawa. JWST knowledge present it’s cooler than anticipated, suggesting a coherent rocky physique somewhat than a unfastened rubble pile.

Preparing for 2032 and Beyond

A 4% likelihood of impression could sound small, but it surely’s sufficient for house specialists to start out planning simply in case. By 2032, we might have moon bases and stations orbiting close by. To shield them—and satellites across the Moon—we have to fastidiously mannequin how particles may fly off and unfold if an asteroid had been to hit.

Future JWST observations scheduled for early 2026 will additional refine the orbit and should cut back the impression chance. Regardless of the result, this case illustrates how next-generation survey telescopes and infrared property, akin to JWST, remodel planetary protection from an Earth-only effort to a complete Earth–Moon system technique.

Watch the full SETI Live conversation with Dr. Franck Marchis and Dr. Andy Rivkin to discover how planetary protection analysis is increasing to guard our nearest neighbor.