Editor’s Note: For the remainder of 2024, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 3rd.
A Two-Month Mini-Moon: 2024 PT5 Captured by Earth from September to November
Published September 2024
Main takeaway:
Carlos de la Fuente Marcos and Raúl de la Fuente Marcos (Complutense University of Madrid) used N-body calculations to explore the orbit of the near-Earth object 2024 PT5. They found that 2024 PT5 would accompany Earth as a “mini-moon” from 29 September 2024 to 25 November 2024. Their predictions suggested that the object, which is thought to be about 33 feet (10 meters) wide, would linger for these two months at a distance several times larger than the distance between Earth and the Moon.
Why it’s interesting:
2024 PT5 would not be the first object to be classified as a mini-moon. Earth snags an asteroid from the swarm of near-Earth objects every 10 or 20 years; some of these objects complete one or more orbits around Earth (“temporarily captured orbiters”) while others fail to circle Earth even once (“temporarily captured flybys”). Eventually, the Sun’s persuasive gravitational pull steals these objects away from Earth. The asteroid 2006 RH120 spent almost exactly a year as a mini-moon in 2006–2007, and 2020 CD3 spent several years as Earth’s companion before departing in 2020. Some asteroids make repeated appearances, like 2022 NX1, which was last seen near Earth in 2022 and will return in 2051. So, while mini-moons are not uncommon, 2024 PT5 stands out as being one of the largest known objects in this class.
What researchers learned from 2024 PT5’s close approach:
As predicted, 2024 PT5 spent two months as a close companion to Earth, though NASA reported that the object was never fully captured by Earth’s gravity. While 2024 PT5 floated near Earth, researchers took the opportunity to study the object more closely. These observations suggested that the asteroid may have once been a part of the Moon — the actual Moon, not a miniature version — that was ejected when an object slammed into the Moon. Alternatively, the asteroid may be a fragment of a larger object that was disrupted. Though 2024 PT5 departed in late November, it’s not gone for long: its next close pass to Earth will take place in January 2025.
Citation
Carlos de la Fuente Marcos and Raúl de la Fuente Marcos 2024 Res. Notes AAS 8 224. doi:10.3847/2515-5172/ad781f