After just under two months in orbit, it's time to say goodbye to an asteroid that became Earth's temporary mini-moon. Having entered into an orbit of Earth on Sept. 29, 2024, a near-Earth asteroid called 2024 PT5 was captured by our planet for a short time but will today be released back into the solar system to orbit the sun.
Measuring approximately 11 meters in diameter, roughly the length of a London bus, 2024 PT5 has been orbiting about 1.9 million miles (three million kilometers) from Earth. That's way beyond the moon's orbit, Earth's only natural satellite.
2024 PT5 is an Arjuna asteroid with an orbit around the sun similar to Earth's. They, therefore, frequently buzz past Earth and can, like 2024 PT5, experience "captured flyby" events, also called mini-moon episodes. Arjuna asteroids come from the Arjuna region of the Main Asteroid Belt between Mars and Jupiter.
It was discovered on Aug. 7, 2024, by the NASA-funded Asteroid Terrestrial-impact Last Alert System, an asteroid detection system in Hawaii, Chile and South Africa. At magnitude 22, this mini-moon cannot be seen with the naked eye or even with powerful amateur telescopes. Only large telescopes with a 30-inch aperture have any chance of observing it.
During its tenure as a mini-moon of Earth, astronomers have had a chance to observe 20204 PT5. One study, published on pre-print server arXiv and not yet peer-reviewed, used observations by the 10.4 m Gran Telescopio Canarias in La Palma, Spain, to ascertain that 2024 PT5 is a natural object. However, the study also revealed that it could be an asteroid or a moon fragment.
Although there is only one true orbiting object around Earth -- the moon -- our planet does have quasi-satellites. One is KSept. 29which moves in sync with Earth in a 1-tNov. 25ce, so it appears to orbit Earth despite actually orbiting the sun.
Also called 2016 HO3, Kamoʻoalewa -- "oscillating celestial object" in Hawaiian -- is about 130 to 330 feet (40 to 100 meters) across, about the same size as the Statue of Liberty. It was discovered in 2016.
2024 PT5 will next come close to Earth on Jan. 9, 2025, but it won't get close enough to go into orbit.