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Asteroid 2024 YR4
Asteroid YR4 might miss the earth. Will it miss the moon, too?
Context: A newly discovered asteroid, 2024 YR4, has captured scientists’ attention for its potential collision with the Moon in 2032. Detected by the ATLAS telescope in Rio Hurtado, Chile, in December 2024, the asteroid initially raised alarms due to its close proximity and uncertain trajectory.
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- Classified as a near-Earth asteroid (NEA) — objects whose orbits bring them within 1.3 times the Earth-Sun distance.
- Initially considered a potentially hazardous object due to its trajectory and estimated size.
Size and Observation
- Early size estimates based on visible-range ground-based telescopes.
- James Webb Space Telescope (infrared observations) revealed the asteroid to be 65 meters wide, approximately the size of a 10-storey building.
- For context, the dinosaur-killing asteroid was 10 kilometres wide.
Impact Risk to Earth
- In February 2025, NASA issued its highest-ever asteroid impact alert: YR4 had a 3.1% chance of colliding with Earth in 2032.
- Later data and analysis revised the probability to negligible, ruling out an Earth impact.
Current Threat to the Moon
- As of April 2, NASA reported:
- 3.8% chance of YR4 impacting the Moon on December 22, 2032.
- 96.2% chance it will miss the Moon entirely.
- Even if it hits the Moon, its orbit won’t change, but the impact would be massive:
- Expected to create a 500- to 2,000-metre-wide crater.
- The explosion would release energy 340 times stronger than the Hiroshima bomb.
Tracking and Modeling Asteroid Paths
- NEAs are mostly discovered via automated sky surveys: Telescopes take successive images, and algorithms identify moving objects.
- Initial orbital paths are uncertain due to limited observation data.
- Scientists use this data to develop probabilistic orbital models.
- As more data becomes available, models are refined and predictions become more accurate.
Asteroid Risk Assessment Tools
- NASA’s Sentry system, which tracks asteroid threats, uses the Torino Scale to categorise risk levels. On this scale, 0 means no risk and 10 means a global catastrophe. YR4 briefly scored a 3 before being downgraded to 0.
- Still, a Moon impact would be scientifically significant. According to Murthy, such an event would provide a rare opportunity to study the lunar regolith—the loose dust and debris covering the Moon’s surface.
- India’s Chandrayaan-2 orbiter and other spacecraft in lunar orbit may capture the moment. And if the impact occurs on the Moon’s near side, telescopes on Earth could record it as well.
- Astronomers are split on whether the flash would be visible to the naked eye.
Visibility of a Moon Impact
- Scientists debate whether a Moon impact would be visible from Earth: Some say the Moon’s brightness will obscure the flash.
- Others, like Prof. Gareth Collins (Imperial College London), argue the impact flash would be visible even in daylight.
- If the impact occurs on the Moon’s near side, it would be observed by telescopes.
- The Chandrayaan-2 orbiter could potentially witness the event.
Broader Implications
- YR4 is expected to fly past Earth again in 2028, giving astronomers a fresh chance to gather data and fine-tune their predictions before the potential 2032 Moon encounter.
- Though YR4 no longer poses a threat to Earth, its discovery and the ensuing analysis underscore a broader concern: Earth is constantly bombarded by space rocks. The 2013 Chelyabinsk meteor, which injured over 1,000 people in Russia, serves as a recent reminder.
- Nugent notes that asteroids are the only preventable natural disaster — given enough time and technology, humanity could one day deflect a truly dangerous rock.
