{"id":15275468,"date":"2026-08-28T10:30:00","date_gmt":"2026-08-28T14:30:00","guid":{"rendered":"https:\/\/www.inthacity.com\/news\/this-cosmic-oddity-blurs-the-line-between-planet-and-moon\/"},"modified":"2026-08-28T10:33:25","modified_gmt":"2026-08-28T14:33:25","slug":"this-cosmic-oddity-blurs-the-line-between-planet-and-moon","status":"publish","type":"post","link":"https:\/\/www.inthacity.com\/news\/this-cosmic-oddity-blurs-the-line-between-planet-and-moon\/","title":{"rendered":"This cosmic oddity blurs the line between planet and moon"},"content":{"rendered":"

A newly discovered cosmic object is unlike any seen before. It\u2019s not a planet. It\u2019s not a moon, either. It\u2019s a third thing we don\u2019t have a name for yet.<\/p>\n

The newfound object is about as massive as Jupiter and orbits a brown dwarf. That\u2019s an object much bigger than a planet, but too small to burn hydrogen and shine as a true star. The brown dwarf, in turn, loops around a star called CD-35 2722.<\/p>\n

This star system is the first known to host an \u201cexosatellite,\u201d<\/a> researchers say. They shared the discovery July 22 in Nature<\/em>.<\/p>\n

The team coined the term \u201cexosatellite\u201d for the new object because no existing word is quite right. It\u2019s not exactly an \u201cexoplanet<\/a>,\u201d a planet around another star. Nor is it an \u201cexomoon<\/a>,\u201d a moon around an exoplanet.<\/p>\n

\n
\n<\/div>
The newfound \u201cmoonish thingy\u201d appears in center about halfway through this animation. Its star (CD-35 2722) \u2014 that glowing dot to the left \u2014 has about half our sun\u2019s mass. A brown dwarf (big foreground object) orbits the star. Orbiting the brown dwarf is the newly discovered object that challenges naming.<\/figcaption><\/figure>\n

An object orbiting a brown dwarf orbiting a star \u201cis so different from the structure of the solar system that all the words we invented to describe the solar system just aren\u2019t really working,\u201d says Kevin Hoy. He\u2019s an astronomer at the University Diego Portales in Santiago, Chile.<\/p>\n

He and others used the Very Large Telescope in Chile to observe the brown dwarf between 2023 and 2026. They saw periodic shifts in wavelengths<\/a> of light emitted by the brown dwarf. This revealed that the gravity<\/a> of a massive object must be tugging it to and fro.<\/p>\n

Astronomers have used the same technique to find planets around other stars<\/a>. But this is the first time the method has turned up what Hoy calls a \u201cmoonish thingy.\u201d That is, something orbiting a bigger something that\u2019s orbiting a still bigger something.<\/p>\n

Does that nested setup make the new object a moon? Hoy doubts it. \u201cIt feels so off,\u201d he says. \u201cWe\u2019re probably not going to get away with calling it an exomoon.\u201d<\/p>\n

Technically a planet?<\/h2>\n

The new finding restarts an old debate about what counts as a planet<\/a>.<\/p>\n

Scientists came up with the current definition of an exoplanet in 2018. The International Astronomical Union, or IAU, devised it. (The same group decided that Pluto is not a planet, but rather a dwarf planet<\/a>, in 2006.)<\/p>\n

That definition lists a couple criteria for an exoplanet. It must be at most 13 times the mass of Jupiter. And it must orbit a star, a brown dwarf or the dense orb left behind after a massive star explodes.<\/p>\n