JACKSONVILLE, Fla. – In an extraordinary celestial event, Earth has been hosting a “mini-moon” the size of a city bus for the past several weeks.
Officially named asteroid 2024 PT5, this object entered Earth’s orbit on Sept. 29 and will remain nearby until Nov. 25, just in time for Thanksgiving.
Unlike Earth’s moon, this mini-moon is a temporary visitor from deep space, poised to return to its solar system trajectory once its Earth-bound journey ends.
What are mini-moons?
Mini-moons are asteroids or space debris that temporarily enter Earth’s gravitational influence, moving into orbit for weeks or months before being flung back into the solar system. While Earth’s orbit occasionally captures such objects, they’re a rare phenomenon.
This latest mini-moon, 2024 PT5, was discovered in August by the Asteroid Terrestrial-impact Last Alert System (ATLAS), a network of telescopes designed to detect objects close to Earth.
Amateur astronomer Tony Dunn provided a simulation on social media showing the asteroid’s path relative to Earth. According to his analysis, 2024 PT5 has been near Earth since July but was only gravitationally captured in late September.
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
The simulation reveals that the asteroid’s path, marked as a red line, traces a partial orbit around Earth, spanning approximately 25% of the planet.
Interestingly, 2024 PT5 won’t complete a full orbit around Earth. This distinction classifies it as a temporarily captured flyby, not a temporarily captured orbiter, which would fully circle the planet.
Such phenomena are influenced by the asteroid’s velocity, trajectory, and Earth’s gravitational pull, creating a delicate balance before the object escapes back into solar orbit. During its visit, 2024 PT5’s geocentric energy (energy relative to Earth) becomes negative, signifying it is temporarily bound to Earth’s gravity. This negative energy will persist for 56.6 days before breaking free of Earth’s gravity after Thanksgiving.
Why does this matter?
Mini-moons like 2024 PT5 offer scientists unique opportunities to study near-Earth objects and their interactions with our planet. They also provide valuable insights into orbital mechanics and Earth’s gravitational field dynamics.
And it may be surprising to know that even our moon is slipping away. Right now, the Moon is moving away from Earth about 5 inches per year—roughly the width of a bottle cap!
Over millions of years, this slow drift could change how the Earth and Moon interact. One day, they might become “tidally locked,” meaning one side of Earth would always face the Moon. But don’t worry this won’t happen for billions of years, long after other big changes to the solar system.