Recently, NASA reported a 3.8% chance that asteroid YR4 could collide with the moon on December 22, 2032, although there is a 96.2% chance it will miss.

About Asteroid YR4

• YR4 is a near-Earth asteroid discovered in December 2024 using the ATLAS telescope in Chile.
  • A near-Earth asteroid (NEA) is a rocky object orbiting the Sun whose path brings it close to Earth, typically within 1.3 astronomical units, posing potential impact risks.

• It orbits the Sun with its closest approach within 1.3 times the Earth-Sun distance.
• It originally triggered NASA’s highest-ever asteroid impact alert in February 2025 due to an initial 3.1% chance of Earth impact.
• Size and Characteristics
  • Comparison: Much smaller than the 10 km asteroid that caused the dinosaur extinction.

Impact Threat Assessment

• NASA initially flagged it as a threat to Earth, but later ruled out significant risk as more data became available.
• Torino Scale: Previously rated at Level 3, later revised to Level 0 (no threat).
• Moon Impact Possibility: A 3.8% chance remains for a lunar collision, with an estimated crater size of 500–2,000 metres.
  • The impact would release energy 340 times greater than the Hiroshima bomb.
• Observational uncertainty is common in early discoveries due to limited data points.
• As more data is collected, especially during YR4’s next Earth flyby in 2028, orbit predictions will be refined.
  • An Earth flyby is a maneuver in which a spacecraft or object passes close to Earth to gain speed or change trajectory using the planet’s gravitational pull.

What Happens If YR4 Hits the Moon?

• The moon’s orbit will not be affected.
• Explosion and crater formation would provide valuable scientific data about the lunar regolith.
• Chandrayaan-2 and other lunar orbiters would likely be able to observe the impact.
• Visibility from Earth is uncertain with some experts suggesting the impact flash could be visible even during daytime, others believe it may be too faint due to the Moon’s brightness.

Planetary Protection: Safeguarding Earth and Beyond

• Legal Basis: Article IX of the Outer Space Treaty mandates countries to prevent harmful contamination and adopt preventive measures.
• ESA Compliance: Adheres to Committee on Space Research (COSPAR) policies; emphasizes:
  • Backward Protection: Prevent contamination of Earth by extraterrestrial material.
  • Forward Protection: Preserve the integrity of extraterrestrial environments and life-detection missions.

Why Does This Matters?

• Even small asteroids like YR4 can cause localized damage in space or on Earth.
  • Past events like the 2013 Chelyabinsk meteor show Earth remains vulnerable to smaller space rocks.
• Large impacts could cause global climate effects by injecting dust into the atmosphere.
• Unlike other natural disasters, asteroid impacts are potentially preventable with early detection and planetary defense systems.

International Collaborations in Planetary Defense

• NASA: Leads planetary defense missions like DART and monitors asteroid threats via Sentry system.
• ISRO: Participates in space surveillance and exploration, collaborating in global asteroid monitoring.
• Global Cooperation: Coordination among space agencies is essential for tracking, modeling, and deflecting NEO threats.

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