Earth has quasi-moons, which are asteroids that orbit the Sun in a path similar to Earth's, but are not gravitationally bound to it. From our perspective on Earth, these objects appear to loop around our planet, creating an illusion of a secondary moon. The most recent discovery is asteroid 2025 PN7, but other known quasi-moons include the stable Kamoʻoalewa (2016 HO3) and Cardea (2004 GU9).
What is a quasi-moon?
Orbital Resonance: Quasi-moons are caught in a 1-to-1 orbital resonance with Earth, meaning they orbit the Sun in about the same amount of time we do. Gravitational "Dance": From Earth's viewpoint, they appear to orbit us, but from a wider solar system perspective, the Sun is the primary force steering their path.
Temporary Companions: They are not permanent satellites like our true moon. Instead, they can remain in this resonant orbit for hundreds or even thousands of years, but they are not truly "stuck" to Earth's gravity.
Recent Discoveries 2025 PN7: This newly discovered quasi-moon is the smallest and least stable known. It measures about 62 feet wide and has remained hidden for decades due to its faintness, visible only with powerful telescopes.
Kamoʻoalewa (2016 HO3): One of the most famous quasi-moons, Kamoʻoalewa has a stable orbit and may be an ancient fragment of the Moon. China's Tianwen-2 mission is planned to collect samples from it.
Why are they important?
Planetary Science: Studying quasi-moons can provide insights into our solar system and the dynamics of near-Earth objects.
Future Missions: They are promising targets for future space missions, offering opportunities for sample collection and scientific exploration. Planetary Defense: Monitoring these objects is important for planetary defense and understanding potentially hazardous asteroids.
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