"In August, an amateur French astronomer, Adrien Coffinet, messaged an email list dedicated to asteroid and comet research with an announcement. He'd identified a new quasi-moon: "2025 PN7 seems to be a quasi-satellite of the Earth," he wrote. Last week, news of the quasi-moon went mainstream, as a surge of headlines declared that Earth officially had a second moon. This isn't exactly right: As several scientists reiterated to me, Earth still only has one real moon."
"A moon is generally understood to be an object that orbits a planet. Beyond that, a more precise, official definition doesn't exist. The International Astronomical Union has been in charge of planetary nomenclature for more than 100 years, but "surprisingly, they have not defined what a moon is," Jean-Luc Margot, a UCLA astronomer, told me. This has created "total ambiguity regarding what is or isn't a moon," Jacqueline McCleary, an observational cosmologist at Northeastern University, told me."
Amateur astronomer Adrien Coffinet identified a quasi-satellite, 2025 PN7, that temporarily accompanies Earth, prompting mainstream headlines calling it a second moon. Earth retains a single permanent natural satellite. Increasing surveys and improved detection have revealed many moonlike objects across the solar system, including dozens of new moons around Jupiter and 128 moons counted around Saturn this year. The International Astronomical Union has not defined what constitutes a moon, producing classification ambiguity. Astronomers debate size thresholds and terminology such as "moonlets" versus official moons as discoveries blur traditional categories.
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