Why in News?
Astronomers discovered asteroid 2025 PN7, a tiny quasi-moon trailing Earth in a Sun-centered orbit since 1957. Unlike short-lived mini-moons, quasi-moons remain for decades. Likely the smallest of its kind, it will stay in Earth’s vicinity for about 126 years.
Description:
Earth’s Co-Orbital Companions:
| Feature | Quasi-Moon (Quasi-Satellite) | Mini-Moon (Temporary Satellite) | Trojan Orbit | Horseshoe Orbit |
| Orbit type | Sun-centered (heliocentric), similar to Earth’s | Captured temporarily by Earth’s gravity | Sun-centered, located at L4/L5 Lagrange points (60° ahead/behind Earth) | Sun-centered, alternates between leading and trailing Earth |
| Bound to Earth? | Not gravitationally bound | Gravitationally bound (for months–years) | Not bound | Not bound |
| Appearance from Earth | Appears to orbit Earth, but is actually orbiting Sun | True (temporary) moon of Earth | Appears as if it’s always ahead or behind Earth | Appears as if it “swings” in a horseshoe path relative to Earth |
| Stability | Decades (e.g., 2025 PN7 ~1955–2085) | Short-term (months to few years) | Stable over long timescales (millions of years for Jupiter’s Trojans) | Intermediate stability |
| Examples | 2025 PN7 (smallest & least stable known), 469219 Kamoʻoalewa | 2024 PT5 (detected in 2024), 2020 CD3 | Jupiter Trojans (thousands), Earth Trojan 2010 TK7 | Earth horseshoe: 3753 Cruithne |
| Significance | Allows long-term study of small asteroids | Useful for studying temporary Earth captures | Show gravitational stability near Lagrange points | Show dynamic orbital evolution around Earth’s path |
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