Is it a planet or a moon? Scientists discover a strange Jupiter-sized world orbiting a brown dwarf in a never-before-seen cosmic system

Astronomers have discovered an unusual Jupiter-sized world that is forcing scientists to reconsider the familiar distinction between planets and moons.

The object is roughly as massive as Jupiter and circles a brown dwarf — an object larger than a planet but too small to sustain the hydrogen fusion that powers ordinary stars. The brown dwarf, meanwhile, is itself orbiting a small star.

The unusual arrangement has led researchers to describe the newly identified body as an “exosatellite”, a term intended to capture its position in a complex orbital hierarchy.


The system, known as CD-35 2722, is being described as the first known system containing such an object.

A cosmic system unlike our own

The discovery was made by a team led by astronomer Kevin Hoy of the University Diego Portales in Santiago, Chile.

Researchers observed the brown dwarf using the Very Large Telescope in Chile on multiple occasions between October 2023 and February 2026. They detected repeated changes in the wavelengths of light coming from the brown dwarf.

Those variations indicated that another massive body was exerting a gravitational pull on it.

This method, known as the radial velocity technique, has been one of astronomy's most successful tools for detecting planets beyond our solar system. It was also used in the discovery of some of the earliest exoplanets.

What makes this observation unusual is not simply the object's size. It is the way the bodies are arranged.

The newly detected world circles the brown dwarf, while the brown dwarf itself follows an orbit around a star.

In other words, the system has a nested structure that has no close equivalent among the planets and moons of our solar system.

Why scientists are debating whether it is a planet

The discovery has revived a much older question in astronomy: What exactly makes an object a planet?

Under the International Astronomical Union's current definition, a planet-mass object orbiting a brown dwarf can be classified as an exoplanet.

That definition, adopted in 2018, does not require the brown dwarf to be the most massive object in the wider system.

Astronomer David Kipping of Columbia University, who has spent years searching for moons around planets outside the solar system, argues that the existing definition points clearly toward a planetary classification.

“If you accept that this is a brown dwarf, that kind of forces the companion to be a planet,” Kipping said.

But Hoy and his colleagues are less comfortable with that description.

Their argument is essentially about context. Although the object's mass may resemble that of a planet, its place in the system makes it behave differently from the planets we are accustomed to seeing.

The planet-moon divide may not be so simple

The debate is complicated by the fact that size alone has never provided a perfect dividing line between planets and moons.

Some of the solar system's largest moons are comparable in size and mass to small planets. Ganymede, Jupiter's largest moon, and Titan, Saturn's largest moon, are both substantially larger than some planetary bodies.

That raises an intriguing thought experiment: if Ganymede orbited the Sun directly, would we instinctively call it a planet? And if Mercury orbited Jupiter instead of the Sun, would its classification change?

Hoy believes the answer illustrates how much planetary terminology depends on an object's relationship with other bodies.

The ancient Greek concept of a planet was tied to movement across the sky — essentially, a “wandering star”. Even after the Copernican revolution changed humanity's understanding of the solar system, orbital motion remained central to the way planets were defined.

More strange worlds could be waiting

CD-35 2722 may not remain unique for long.

Another team reported in January a possible detection of a similar satellite-like object around a brown dwarf in a separate star system. That candidate is estimated to have about half the mass of Jupiter, although its existence still requires confirmation.

If additional systems like these are discovered, astronomers could be faced with an expanding collection of worlds that do not fit neatly into familiar categories.

The implications could be particularly important for the search for exomoons — moons orbiting planets outside our solar system. Despite years of searching, confirmed exomoons remain elusive.

Kipping sees the new discovery as a sign that astronomers may finally be approaching that frontier.

The newly identified object may not technically be an exomoon. But its discovery demonstrates that planetary systems can be considerably more complicated than the simple star-planet-moon arrangement that dominates our understanding of the cosmos.

And as increasingly sensitive telescopes reveal more unusual systems, astronomers may have to rethink not only what these worlds are made of, but also the labels humans use to describe them.