So soon? Bidding goodbye to our recently arrived mini moon

The Earth is parting company with an asteroid called 2024 PT5 that has been tagging along as a "mini moon" for the past two months. The harmless space rock moved away on Monday, overcome by the stronger gravitational force of the Sun, Forbes reported.

Discovered on August 7, 2024, by the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS), asteroid 2024 PT5 has been following a horseshoe-shaped trajectory around Earth. Measuring approximately 11 meters in diameter, roughly the length of a London bus, the asteroid has been too small and faint to be seen without a powerful telescope, with a magnitude of 22, making it invisible to the naked eye and even to powerful amateur telescopes.

Although technically not a moon, NASA emphasizes that the asteroid was never captured by Earth's gravity and did not achieve a complete orbit. The moon is Earth's only natural satellite. However, Earth's gravitational influence caused 2024 PT5 to follow a path resembling that of a "mini moon" during its close approach.

Astrophysicist brothers Raúl and Carlos de la Fuente Marcos from the Complutense University of Madrid identified the asteroid's "mini-moon" behavior. Raúl de la Fuente Marcos explained the asteroid's upcoming trajectory: "By the time the asteroid returns next year, it will be moving too fast—more than double its speed in September—to stay," according to Republic World.

NASA plans to use a radar antenna to observe the 11-meter asteroid 2024 PT5 in January. Specifically, NASA will track the asteroid for more than a week in January using the Goldstone solar system radar antenna in California's Mojave Desert, which is part of the Deep Space Network. "NASA describes the asteroid as 'an interesting object' worthy of study," Republic World states. Primera Hora adds that the Goldstone antenna is part of NASA's Deep Space Network.

In January 2024, the asteroid 2024 PT5 will pass as close as 1.8 million kilometers (1.1 million miles) from Earth, maintaining a safe distance before moving further away in the solar system while orbiting around the Sun. However, "after its January visit, the asteroid 2024 PT5 will zoom farther into the solar system while orbiting the Sun and will not return until 2055," according to Republic World.

In 2055, the asteroid will return almost five times farther than the Moon.

One study, published on the pre-print server arXiv and not yet peer-reviewed, used observations by the 10.4 m Gran Telescopio Canarias in La Palma, Spain, to ascertain that 2024 PT5 is a natural object. The study also revealed that 2024 PT5 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 quasi-satellite is Kamoʻoalewa, also called 2016 HO3, which moves in sync with Earth in a 1:1 ratio, so it appears to orbit Earth despite actually orbiting the Sun. Kamoʻoalewa is about 130 to 330 feet (40 to 100 meters) across, about the same size as the Statue of Liberty, and was discovered in 2016.

Arjuna asteroids frequently pass close to Earth and can 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.

Only large telescopes with a 30-inch aperture have any chance of observing 2024 PT5. Currently, the asteroid is more than 3.5 million kilometers (2 million miles) away from Earth and is too small and faint to be seen without a powerful telescope, with a magnitude of 22, making it invisible to the naked eye and even to powerful amateur telescopes.

Forbes, Republic World, El Nuevo Día, Primera Hora, and The Epoch Times were among the news websites that reported on the mini-moon's departure from orbit.

This article was written in collaboration with generative AI company Alchemiq