Earth Has Had A Second Moon Many Times—Including Recently—Thanks To Asteroids
We've all heard news or stories about asteroids flying dangerously close to our planet, a near-collision course that, if pushed just slightly, could have caused disaster. Seeing as they're big hunks or rocks traveling unimaginably fast, it's hard to imagine them not doing massive damage wherever they land.
However, there was a way for an asteroid to approach Earth without it being a doomsday scenario. Rather than colliding into us, it joined us!
Entering Our Orbit
Between September 29 and November 25 2024, Earth experienced a fascinating phenomenon that left it with twice the orbital bodies than it normally has. It gained a second moon.
Asteroid 2024 PT5 came and went around us with no risk of collision. Instead, it became a 'Near-Earth object,' or NEO. It was just near enough to get pulled into Earth's orbit alongside the moon. It was only around for a little while, though; it stuck around for about two months before blasting off and leaving us with only one moon once more.
A Mini-Me
Why was it a "second moon", though? Researchers called the asteroid a 'mini-moon' because it followed the same orbit as the moon!
"NEOs that follow horseshoe paths, and approach our planet at close range and low relative velocity, may undergo mini-moon events in which their geocentric energy becomes negative for hours, days or months, but without completing one revolution around Earth while bound," read the Research Notes of the American Astronomical Society, published by Carlos and Raúl de la Fuente Marcos.
Previous Passers By
This wasn't the first time Earth has had a mini-moon visitor either. Both in 1981 and 2022, an asteroid named NX1 hung around Earth's orbit for a while. There was also one in 2020, the CD3 mini-moon.
The previous asteroid visitor was captured by a NASA-funded program, the Asteroid Terrestrial-impact Last Alert System, or "ATLAS", and was first spotted on a monitoring system in South Africa back in August. It was notably smaller than our regular moon, only measuring about 10 meters in length.
A Belt Of Possibilities
De la Fuente Marcos, lead researcher, and Universidad Complutense de Madrid professor, told Space.com, "The object that is going to pay us a visit belongs to the Arjuna asteroid belt, a secondary asteroid belt made of space rocks that follow orbits very similar to that of Earth at an average distance to the sun of about 93 million miles (150 million kilometers).
"Objects in the Arjuna asteroid belt are part of the near-Earth object population of asteroids and comets."
Not Long Enough
While sitting in our orbit, PT5 didn't actually complete a full revolution around the planet. It fell back out before making its way around the planet and went on its way.
"You may say that if a true satellite is like a customer buying goods inside a store, objects like 2024 PT5 are window shoppers," de la Fuente Marcos explained.
Unfortunately, despite how long it stuck around for and its proximity to Earth, it was nigh-impossible to see the mini-moon with the naked eye.
Just Out Of View
It was tough to see with a telescope, too. As de la Fuente Marcos explained, "The object is too small and dim for typical amateur telescopes and binoculars. However, the object is well within the brightness range of typical telescopes used by professional astronomers."
If you missed your chance to see it last time, you might get another in... 30 years. The original Research Notes described that "after completing the mini-moon episode," 2024 PT5 will come back to "the neighborhood of Earth" until in 2055.
