{"id":257463,"date":"2025-10-28T22:47:26","date_gmt":"2025-10-28T22:47:26","guid":{"rendered":"https:\/\/www.newsbeep.com\/us\/257463\/"},"modified":"2025-10-28T22:47:26","modified_gmt":"2025-10-28T22:47:26","slug":"no-one-actually-knows-what-a-moon-is","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/us\/257463\/","title":{"rendered":"No One Actually Knows What a Moon Is"},"content":{"rendered":"

The Atlantic Daily, a newsletter that guides you through the biggest stories of the day, helps you discover new ideas, and recommends the best in culture. Sign up for it here.<\/a><\/p>\n

In August, an amateur French astronomer, Adrien Coffinet, messaged an email list dedicated to asteroid and comet research with an announcement. He\u2019d identified a new quasi-moon: \u201c2025 PN7 seems to be a quasi-satellite of the Earth,\u201d he wrote. Last week, news of the quasi-moon went mainstream, as a surge of headlines declared that Earth officially had a second moon.<\/p>\n

This isn\u2019t exactly right: As several scientists reiterated to me, Earth still only has one real moon. But as researchers have discovered more moonlike objects in our solar system\u2014including 128 moons orbiting Saturn just this year\u2014our concept of what counts as a moon has been forced to expand. Now it\u2019s approaching a breaking point.<\/p>\n

A moon is generally understood to be an object that orbits a planet (although what counts as a planet is itself a contentious<\/a> matter). Beyond that, a more precise, official definition doesn\u2019t exist. The International Astronomical Union has been in charge of planetary nomenclature for more than 100 years, but \u201csurprisingly, they have not defined what a moon is,\u201d Jean-Luc Margot, a UCLA astronomer, told me. This has created \u201ctotal ambiguity regarding what is or isn\u2019t a moon,\u201d Jacqueline McCleary, an observational cosmologist at Northeastern University, told me.<\/p>\n

Consider moon size. Technological advancements have enabled scientists to better identify ever smaller objects in space, but they have not agreed where to draw the line between a moon and a (relatively) tiny rock. When Galileo cast a homemade telescope toward the night sky and discovered Jupiter\u2019s four largest moons, he at first mistook them for distant stars; the planet now has 95 official moons. Astronomers also have found thousands of other satellites in the gas giant\u2019s orbit: Should those count as moons? Some have taken to calling them \u201cmoonlets\u201d instead.<\/p>\n

In recent decades, scientists have discovered more moonlike objects in proximity to our own planet, too, including a handful of small asteroids that temporarily enter our orbit. Some people call them \u201cmini-moons,\u201d although it\u2019s \u201cnot a term that has a widespread definition,\u201d cautioned Teddy Kareta, an astronomer at Villanova University. Last year, one such object entered Earth\u2019s orbit but left after just two months. Many put that satellite in the mini-moon category, but Kareta worried that, although fun, the term was misleading. That \u201cmini-moon\u201d didn\u2019t even complete a full rotation around Earth.<\/p>\n

\u201cQuasi-moons\u201d are not actually very moonlike. These satellites can appear as if they are orbiting Earth, but in reality they are orbiting the sun. That makes the term \u201ca bit of a misnomer,\u201d Margot told me. Other planets have quasi-moons too: The first one to be discovered, a temporary satellite of Venus, was named<\/a> Zoozve after an artist erroneously transcribed its original name, 2002VE.<\/p>\n

Earth has roughly half a dozen quasi-moons, and in this pantheon, our new one is a bit of a flighty dweeb\u2014roughly the size of a small office building, McCleary said. \u201cIf the other quasi-moons are like albatross circling our ship on our journey around the sun, then this one is maybe more of a hummingbird,\u201d Asa Stahl, an astronomer and science editor at the Planetary Society, told me. Although it was only just discovered, this asteroid has been running in an Earth-like orbit for some 60 years; in another 60 or so, it will lose its quasi-moon status. Its ultimate path is somewhat mysterious, but Coffinet\u2019s simulations suggest<\/a> that thousands of years from now, it might cross Mars\u2019s orbit.<\/p>\n

In the coming years, astronomers are likely to locate more ambiguous moonlike objects. New imaging technology at the Vera C. Rubin Observatory, for instance, is supercharging our ability to peer into the sky, while progress in software development is improving analysis of the images that observatories capture. As these maybe-moons pile up, \u201cthe lack of a clear definition of moon\u2014or quasi-moon, or mini-moon\u2014causes about as much confusion and consternation among scientists as it does in the public,\u201d Kareta explained. In a recent paper, he added an entire \u201cterminology\u201d section to help define various terms. Margot suggested that the International Astronomical Union \u201crevisit these issues and come up with proper definitions that are precise and general for planets and also for moons.\u201d But he\u2019s not expecting the group to act anytime soon: There\u2019s still a lot of \u201ctrauma\u201d\u2014to use Margot\u2019s words\u2014left over from the aughts, when the IAU changed the definition of a planet. (RIP Pluto.)<\/p>\n

Earth\u2019s own moon\u2014the one that hangs above us, whose light \u201cstretches over salt sea equally and flowerdeep fields,\u201d as Sappho once noted\u2014is itself astounding. No other planet in our solar system has exactly one moon. The leading theory behind the moon\u2019s formation suggests that in the earliest days of our solar system, baby Earth was flying solo until, after some tens of millions of years, a Mars-size object collided with it and sent debris flying into space. After learning of mini-moons and quasi-moons and moonlets, I wondered if the Earth might actually have a second true moon, which has somehow managed to evade detection. When I asked the astronomers, they were skeptical, but none denied the possibility. \u201cIt\u2019s certainly conceivable,\u201d McCleary told me. \u201cIf there is one, I think we\u2019ll probably find it in the next 10 years,\u201d she said.<\/p>\n

Article originally published at The Atlantic<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"The Atlantic Daily, a newsletter that guides you through the biggest stories of the day, helps you discover…\n","protected":false},"author":2,"featured_media":257464,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[32],"tags":[139320,139317,139318,139321,139319,5005,79],"class_list":{"0":"post-257463","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-adrien-coffinet","9":"tag-international-astronomical-union","10":"tag-jean-luc-margot","11":"tag-northeastern-university","12":"tag-objects-in-space","13":"tag-our-solar-system","14":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/257463","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=257463"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/257463\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/257464"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=257463"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=257463"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=257463"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}