Starting on September 29, 2024, Earth will briefly have a second "moon" as a small asteroid, 2024 PT5, gets captured by our planet's gravity. This mini-moon will stick around for nearly two months before continuing its journey through space.
What is a Mmini-moon, and How Does it Form?
A mini-moon occurs when a small celestial object, such as an asteroid, is temporarily caught in Earth's gravitational pull. Unlike our permanent Moon, these objects don't stay in orbit for long. Their orbits are unstable, and after a brief stint as Earth's companion, they eventually break free. This phenomenon is rare but not unheard of. In the past, a few other objects have become mini-moons for short periods, offering researchers valuable insights into the gravitational dynamics between Earth and small asteroids.
Mini-moons form under specific conditions—when an asteroid approaches Earth at just the right speed and trajectory to get pulled into a temporary orbit. Even slight variations in speed or angle can determine whether an object will circle the Earth or continue on its path. By studying these interactions, astronomers can learn more about how gravity influences smaller bodies in our solar system.
Asteroid 2024 PT5: Earth’s Fleeting Companion
Asteroid 2024 PT5 was first discovered on August 7, 2024, by the Asteroid Terrestrial-Impact Last Alert System (ATLAS). Measuring about 33 feet (10 meters) in diameter, this small asteroid will make a temporary loop around Earth starting on September 29, staying in orbit until November 25, 2024. According to researchers Carlos and Raúl de la Fuente Marcos, 2024 PT5 will not complete a full orbit. Instead, it will make a brief flyby, classified as a temporarily captured flyby, before breaking free of Earth’s gravitational influence and returning to its original orbit around the Sun.
Though 2024 PT5’s stay is short, it presents a unique opportunity for astronomers to study how Earth’s gravity can alter the paths of small asteroids. This asteroid is part of the Arjuna group, a collection of near-Earth objects with orbits similar to Earth’s. Its relatively low velocity and close approach will make it possible for our planet to temporarily pull it into its orbit.
Amateur astronomer Tony Dunn shared a simulation of 2024 PT5's path on X (formerly Twitter), illustrating the asteroid's brief time as Earth’s mini-moon:
Newly-discovered #asteroid 2024 PT5 is about to undergo a "mini-moon event" when its geocentric energy becomes negative from September 29 - November 25.https://t.co/sAo1qSRu3J pic.twitter.com/pVYAmSbkCF
— Tony Dunn (@tony873004) September 10, 2024
Will You be Able to See the Mini-moon?
Despite the excitement surrounding Earth’s temporary mini-moon, 2024 PT5 is far too small and dim to be seen with the naked eye. With a magnitude of 22, it will remain invisible even to most backyard telescopes. Objects need a magnitude of 6 or lower to be visible without specialized equipment, so only advanced observatories will be able to track its path.
Though it may not be visible, astronomers will closely monitor the asteroid’s movements using radar and other technologies. Observing how Earth’s gravity influences 2024 PT5 can provide valuable data for understanding how asteroids behave when they approach Earth. For space agencies, tracking mini-moons like this could also play a role in future asteroid exploration missions.
Why Mini-moons Matter for Science
While mini-moons like 2024 PT5 are small and fleeting, they offer critical insights into the dynamics of near-Earth objects. Understanding how Earth temporarily captures these asteroids helps astronomers refine models of gravitational interaction, improving predictions for how other asteroids might behave when passing close to our planet. This knowledge is crucial, particularly for preparing to deal with potentially hazardous objects that could pose a threat in the future.
Moreover, mini-moons are of interest to the growing field of asteroid mining and space exploration. These small objects, being relatively close and easy to access, offer promising targets for missions that aim to study or even extract valuable resources from asteroids. As technology advances, mini-moons could become testbeds for new exploration techniques, helping pave the way for more ambitious space missions.
While 2024 PT5’s time as Earth’s mini-moon may be brief, its presence highlights the fascinating and ever-changing dynamics of our planet’s interaction with small celestial bodies.