Earth had a temporary mini-moon for the past two months as asteroid 2024 PT5 orbited the planet from September 29. The small asteroid left Earth’s orbit on November 25, with its next close approach scheduled for November 8, 2055, according to Space.com. Measuring about 10 meters (33 feet) in diameter, 2024 PT5 was too small to be seen with the naked eye, unlike larger asteroids such as Apophis or Bennu.
NASA’s Asteroid Terrestrial-impact Last Alert System (ATLAS) discovered 2024 PT5 on August 7, 2024, from its Hawaii observatory. The asteroid’s designation reflects the year of discovery and its sequence. ATLAS, which tracks potentially hazardous asteroids, also discovered comet Tschunishan-Atlas, visible between September 27 and October 24.
Classified as an Apollo-class near-Earth object (NEO), 2024 PT5 temporarily orbited Earth before returning to its regular orbit around the Sun. The asteroid did not pose any collision threat during its stay.
Mini-moons are asteroids that get caught in Earth’s gravity during a flyby and orbit the planet briefly. NASA monitors around 28,000 NEOs, including such temporary satellites.
Historically, mini-moons are rare. Asteroid 2022 NX1 orbited Earth in 1981 and again in 2022. Asteroid 2006 RH120 remained in orbit for a year, from 2006 to 2007. In 2020, a piece of space debris from a 1966 rocket launch became the third mini-moon.