27 days, 7 hours, 43 minutes, and 13 seconds
(Janet Loehrke USA TODAY, 2024)
This is the approximate period of the sidereal month. In other words, it takes that amount of time for the Moon to make one full orbit around the Earth relative to the celestial sphere, the apparently still, distant background of stars.
Beginning just next week on September 29th, and for about 2 of these sidereal months, the Moon will, in fact, not be alone in our orbit! Meet 2024 PT5:
2024 PT5 is a near-Earth asteroid that was discovered by ATLAS South Africa on August 7th, 2024. However small it may be (11m, 36ft), I would consider it a welcome (albeit temporary) addition to the family. We know and love our Moon, but a visitor is always a welcome opportunity for more thorough study into the smaller objects that inhabit our solar system.
In actuality, 2024 PT5 is one of many thousands just like it, but I do not believe that makes its visit any less significant. The asteroid, much like its little siblings scattered throughout the solar system, typically revolves around the Sun. But from September 29th to November 25th, its path has brought it close enough to Earth to be temporarily caught in our gravity. Thus, it will hang around for a while. And while it is in such close proximity, telescopes and other facilities around the world will be using this opportunity to study it very closely, as this sort of thing does not happen often. That is to say, however, that this sort of thing has actually happened before!
The earliest known instance of a temporary satellite of Earth's was another, quite similar asteroid known as 2006 RH120, discovered in, you guessed it, 2006. Since then, there have been a handful of similar objects that have been spotted, one as recent as 2022 (2022 NX1). Besides the rather creative naming convention given to these objects, they may hold some fascinating insight into the genesis of the solar system and how it has evolved with time. One interesting hypothesis states that Mars' two moons, Phobos and Deimos, may have actually been objects originating from the asteroid belt, and very similarly to 2024 PT5 and Earth, Mars captured the two strangely-shaped bodies when its path around the Sun crossed those of Phobos and Deimos. This hypothesis states that Mars captured the two in its orbit, and they simply never left!
References
Wikimedia Foundation. (n.d.). Orbit of the Moon. Wikipedia. https://en.wikipedia.org/wiki/Orbit_of_the_Moon
Wikimedia Foundation. (n.d.-a). 2024 PT5. Wikipedia. https://en.wikipedia.org/wiki/2024_PT5
Loehrke, J. (2024, September 19). Earth is about to get a mini-moon (temporarily). what to know about asteroid 2024 PT5. USA Today. https://www.usatoday.com/story/graphics/2024/09/19/asteroid-mini-moon-2024-pt5/75260498007/
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