On September 29, Earth’s gravitational influence temporarily made asteroid 2024 PT5 another moon.
However, 2024 PT5 is only 10 meters across, smaller than the Moon (3,475 kilometers) and has a magnitude of only 22. Higher magnitudes mean less bright objects. For example, the Sun has a magnitude of -26.8, the full Moon is -12.7, and the visible limit of the human eye is 7.
This means that Earth’s temporary moon is invisible to the naked eye, as is the case with conventional telescopes, and does not alter the night sky on Earth in any way.
2024 PT5 was discovered on August 7, 2024, by NASA’s Asteroid Terrestrial-impact Last Alert System (ATLAS) telescopes. It is predicted to be an Arjuna-class asteroid with a similar orbit around the Sun as Earth and is scheduled to make an impact with Earth between September 29 and November 25, 2024.
During its 56 days as a temporary moon, 2024 PT5 will enter an Earth-centered horseshoe orbit, an unstable temporary orbit at a distance of about 3.4 million to 4 million kilometers from Earth and a relative speed of 7 to 1,577 kilometers per hour, before receding back into deep space.
After leaving Earth’s temporary moon status, asteroid 2024 PT5 is scheduled to make its next close approach to Earth on January 9, 2025, at a distance of approximately 1,800,000 kilometers, and its next close approach on November 8, 2055.
Astronomers have previously discovered temporary moons of Earth, such as asteroids 2006 RH120, 2020 CD3, and 2022 NX1. These moons are pulled by Earth’s gravity into temporary horseshoe orbits for a short period of time before falling back into orbit around the Sun. They are not stable orbits like the moons we can see with the naked eye.
Saturn currently has the most moons in the Solar System, with 146 confirmed moons, followed by Jupiter with 95. Only one of Earth’s natural moons is in a long-term stable orbit, although it recedes from Earth at a rate of about 3.8 centimeters per year.
The discovery of asteroid 2024 PT5 by the research teams Carlos de la Fuente Marcos and Raúl de la Fuente Marcos was published in the September 2024 issue of the American Astronomical Society research journal.
Image: (Asteroid simulation) ESA/P.Carril
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