From 3753 Cruithne to 2024 Discoveries: a History of Earth's Temporary Moons

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Astronomers transitioned from theoretical models of mini-moons to physical confirmation in September 2006. The Catalina Sky Survey in Arizona spotted a tiny, fast-moving object designated 2006 RH120. Initially suspected to be a spent Apollo-era rocket booster, spectral measurements confirmed it was an asteroid roughly four meters across. It completed four distinct orbits around Earth before solar radiation pressure and orbital perturbations expelled it back into an independent solar orbit in June 2007.

Fourteen years passed before astronomers verified another captured mini-moon. In February 2020, observers at the Mount Lemmon Observatory identified 2020 CD3, an asteroid about the size of a compact car. Orbital reconstructions indicated that Earth had captured 2020 CD3 roughly three years earlier, holding it in an erratic loop before releasing it into deep space in March 2020.

Late 2024 brought renewed public fascination when the Asteroid Terrestrial-impact Last Alert System (ATLAS) detected 2024 PT5. Originating from the Arjuna asteroid belt, this ten-meter object underwent a brief gravitational capture from September 29 through November 25, 2024. Unlike 2006 RH120, 2024 PT5 did not complete a full 360-degree loop around Earth; it executed a horseshoe-shaped deflection before departing.