Earth to Temporarily Gain a “Second Moon” This Fall, Astronomers Say

In an exciting celestial development, Earth will soon have a temporary “second moon” starting this fall, but stargazers may be disappointed to learn that this new visitor will be too small to see without professional equipment. According to a study published in the Research Notes of the American Astronomical Society (AAS), the object in question, named 2024 PT5, is an Arjuna asteroid—a type of near-Earth object that shares a similar orbit to our planet.

Arjuna asteroids are small celestial bodies that have low-eccentricity, low-inclination orbits, and an Earth-like period, making them intriguing to astronomers. These objects can become temporary moons, or “mini-moons,” when they get caught in Earth's gravitational pull for short periods.

What Is a Mini-Moon?
Though it may sound extraordinary, the phenomenon of a mini-moon is not unprecedented. These events happen when near-Earth objects (NEOs) follow a path that brings them close to our planet at a low velocity. As their geocentric energy drops, they can become temporarily captured by Earth’s gravity, sometimes lasting for days or even months.

However, unlike Earth’s permanent moon, 2024 PT5 will not complete a full revolution around our planet before it escapes back to its sun-centered orbit. It’s essentially a brief “flyby” event, where the object is temporarily caught but not permanently bound to Earth.

Rare but Fascinating Events
Carlos de la Fuente Marcos, an astronomer from Universidad Complutense de Madrid, explains that such events are common in the astronomical world, but long capture episodes are rare—occurring only once every 10 to 20 years. The latest instance of this phenomenon occurred with the NEO 2022 NX1, which briefly orbited Earth in 1981 and again in 2022.

“These are like window shoppers,” de la Fuente Marcos explained in an interview with Space.com. “They come close, but don’t stick around long enough to buy anything.”

When and How to Observe 2024 PT5
2024 PT5 is set to appear on September 29 and will remain in Earth’s vicinity until November 25. Unfortunately for casual skywatchers, the mini-moon is too small to be visible to the naked eye or even with regular binoculars. According to Professor Marcos, even a 30-inch telescope with a CCD or CMOS detector would be required to catch a glimpse of it.

"A human eye behind the telescope will not be enough," Marcos added, emphasizing the need for professional equipment to observe this rare phenomenon.

Despite its invisibility to most stargazers, 2024 PT5’s temporary visit serves as a reminder of the complex and ever-changing dynamics of our solar system.

While Earth’s new “second moon” may not last long, or be visible without specialized equipment, its presence reminds us of the fascinating cosmic events that happen around us regularly. As scientists continue to observe and study these near-Earth objects, each event offers new insights into the mysteries of our universe.

Be sure to mark your calendars for the brief appearance of 2024 PT5 between September and November 2024—an extraordinary celestial visitor, even if only seen through the lens of advanced telescopes.