Key Terms & Concepts — UPSC Mains
Near-Earth Objects
"Asteroids and comets whose orbits bring them within 1.3 Astronomical Units of the Sun — monitored for potential Earth impact"
Near-Earth Objects (NEOs) are asteroids and comets whose orbital paths bring them within approximately 1.3 Astronomical Units (AU) of the Sun, meaning their orbits approach or cross Earth's orbit. NEOs are classified into three main types: Apollo asteroids (orbits cross Earth's orbit, semi-major axis > 1 AU), Amor asteroids (orbits between Earth and Mars), and Aten asteroids (orbits mostly inside Earth's orbit). Potentially Hazardous Asteroids (PHAs) are a subset of NEOs that come within 0.05 AU of Earth and are larger than 140 metres. NASA's Planetary Defense Coordination Office (PDCO) coordinates global monitoring.
NEOs are regularly tested in UPSC GS-3 (Science & Technology). The DART mission (NASA, 2022) which deliberately impacted asteroid Dimorphos, and the asteroid 2024 YR4 (briefly had 3.1% Earth impact probability, later revised to zero) are recent current affairs. Know the key institutions and classification system.
- 1 NEO = asteroid or comet within 1.3 AU of Sun (1 AU = Earth-Sun distance, ~150 million km)
- 2 PHA (Potentially Hazardous Asteroid) = NEO closer than 0.05 AU to Earth + diameter > 140 m
- 3 Apollo asteroids — cross Earth's orbit; semi-major axis > 1 AU (2024 YR4 is Apollo-type)
- 4 Amor asteroids — orbit between Earth and Mars; do not currently cross Earth's orbit
- 5 Aten asteroids — orbit mostly inside Earth's orbit; can still cross it at points
- 6 ATLAS (Asteroid Terrestrial-impact Last Alert System) — NASA-funded early warning telescope network (Hawaii + Chile + S. Africa)
- 7 NASA PDCO — Planetary Defense Coordination Office; coordinates NEO monitoring globally
- 8 DART mission (2022) — NASA's first planetary defence test; impacted Dimorphos asteroid, changed its orbit
- 9 Asteroid 2024 YR4 — discovered by ATLAS Chile; Apollo-type; 53-67 m diameter; confirmed NO Moon impact in 2032
- 10 Main Asteroid Belt — between Mars and Jupiter; source of most NEOs through gravitational perturbations
Asteroid 2024 YR4 was briefly classified as having a 3.1% probability of hitting Earth in 2032 — the highest ever recorded. Subsequent observations confirmed it will not impact Earth or Moon, but the episode highlighted the need for continuous NEO monitoring systems like ATLAS.