Scientists working at the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile have detected evidence for an unusual, ‘moon-like object’ in the CD-35 2722 system that doesn’t appear to orbit a planet.

The research team behind the discovery said the unusual object, which orbits a brown dwarf that orbits a large, Sun-like star, doesn’t fit normal astronomical categories, leaving them unsure what to name it.

If confirmed, the unusual space object would be the first moon without a host planet ever discovered. Such a confirmation would also make the newly termed “exosatellite” the first exomoon of any type discovered outside our Solar System.

Moon-Like Object Part of ‘Super Weird’ System

According to a statement announcing the moon-like object, ESO student Kevin Hoy had been monitoring the CD-35 2722 star system for months. The measurements that spotted the new, moon-like object were taken with the observatory’s CRIRES+ instrument using the radial velocity method that spotted the first planet around a Sun-like star.

During that time, the researcher and lead author of a study detailing the find said he noticed the system was “super weird” compared to our local Solar System. While the star at the center of the system, with a mass of about half of our Sun, was not unusual, they also determined that it is orbited by a brown dwarf. Brown dwarfs are astronomical objects too small to be a star, but too massive to be a planet, making the pairing unusual. Still, it was not unheard of.

However, according to Hoy, when the team spotted a third, smaller object in the system, they were left confused. Measurements indicated it is at least as massive as Jupiter, suggesting it may be a moon orbiting the Brown Dwarf, only without a host planet.

“The satellite we report is a giant gaseous body orbiting a highly massive companion, itself several times the mass of Jupiter,” explained Alice Zurlo, Director of the Millennium Nucleus of Young Exoplanets and their Moons (YEMS) in Chile project and collaborator on the study.

Mysterious ‘Exosatellite’ Defies Traditional Classification

The team has temporarily named the moon-like object an “exosatellite.” However, Hoy said the object’s status as a ‘third wheel’ in the system makes them want to classify it as a moon, “even if it is nothing like the small, rocky moons we have in our system.”

“This system is somewhat hard to define using Solar-System-based words like ‘planet’ and ‘moon’,” the researcher explained. “The exosatellite is clearly massive enough to be a planet, but it does not orbit a star, though it orbits an object that orbits a star.”

Director Zurlo said the differences between the observed system and our own Solar System have added to the difficulty in labeling the moon-like object.

“We have a clear delineation between the planets and the Sun in the Solar System, so defining things like moons is simple,” Zurlo explained. “In the CD-35 2722 system, where we are blurring the lines between stars, planets, and moons, the whole thing becomes more complicated to describe.”

“This System is Truly Unique and Represents a Breakthrough”

When discussing the significance of the moon-like object, Director Zurlo said detecting satellites in other systems will help researchers better understand the diversity in formation and evolution of planets, moons, and other moon-like objects. The director also noted the historical nature of the detection.

“As exotic as it is, this system is truly unique and represents a breakthrough: the first plausible detection of an exosatellite,” the researcher explained.

Moving forward, the team said the increased sensitivity of the 39-meter mirror on the ESO’s in-development Extremely Large Telescope (ELT) will allow for the detection of even smaller moons, including potentially spotting moons the size of Earth’s largest satellite. The researchers said such detections will likely force the astronomical community to reconsider how planetary objects are labeled, especially those in systems so radically different from our own.

The study “Planetary-mass exosatellite detected around the substellar companion of a star” was published in the journal Nature.

Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org.

Face à l’omniprésence des PFAS, changer de poêle ne suffira pas. Il est temps de libérer les citoyens de cette responsabilité et de faire porter la réponse à la collectivité. En Allemagne, des chercheurs développent justement des technologies de rupture capables de briser ces « polluants...

Some of the most promising locations to search for possible alien megastructures, known as Dyson spheres, may not be stars like the Sun, but rather the galaxy’s smallest and dimmest stars.

Physicist Freeman Dyson introduced the idea of a Dyson sphere in 1960, describing it as a shell or, more realistically, a swarm of orbiting collectors that could capture most of a star’s energy. This concept has interested scientists searching for signs of advanced technology, but the question of how such a structure would appear in astronomical observations remained unknown.

Now, a new study, available on the arXiv preprint server, suggests that one of the coldest objects in a stellar system could, in principle, be an artificial megastructure rather than a natural astronomical object.

Amirnezam Amiri, a physicist at the University of Arkansas, explored the question of Dyson spheres by modeling these hypothetical megastructures around two often-overlooked types of stars: red M-dwarfs and white dwarfs. Amiri credits discussions with Harvard astronomer and founder of the Galileo Project, Avi Loeb, with helping shape the study.

Small, Dim, and Built to Last

Red dwarfs make up about 70% of the stars in the Milky Way. These stars burn slowly and can remain stable for trillions of years, much longer than the universe has even existed so far. White dwarfs offer a different benefit. As the dense remnants of stars like the Sun, they shrink to about 1% of their original size. This means a Dyson swarm could orbit much closer, requiring less material and a smaller structure than one built around a star like the Sun.

Amiri’s study explores how astronomers could detect such structures. Both red dwarfs and white dwarfs are dim enough that the infrared heat emitted by a Dyson swarm would stand out more clearly against the star’s own light.

Reading the Wreckage on a Star Chart

Astronomers use the Hertzsprung-Russell diagram to classify stars by temperature and brightness, and this tool is central to Amiri’s analysis. A Dyson swarm would not destroy a star’s energy, but would capture its light and re-emit it as heat at much longer wavelengths. 

In the new model, a star with a Dyson swarm would appear on the H-R diagram at the same luminosity but shifted dramatically toward the cool end. For instance, a red dwarf at about 3,000 K could appear surrounded by a shell as cold as 50 K, a difference of about two orders of magnitude. No known stars naturally occupy this region of the H-R diagram.

Identifying Factors

Dust and distant galaxies can also produce strong infrared emissions, so astronomers cannot identify a Dyson swarm using temperature alone. Amiri’s model points to a more complex set of clues. A true Dyson swarm would not show the silicate dust features seen in normal dusty disks, so its spectrum would be unusually smooth for an object with strong infrared emission.

Additionally, if the swarm consists of many separate collectors rather than a solid shell, there would be gaps that cause irregular, non-stellar flickering as the pieces move. Each of these signs can have natural causes, but finding them together is rare and hard to explain without considering artificial structures.

Future Observations

Astronomers can carry out this search using existing telescopes. The James Webb Space Telescope’s infrared instruments are already designed to detect faint, cold signals like these. The Vera C. Rubin Observatory’s new sky survey and the Nancy Grace Roman Space Telescope, which is expected to launch later this year, will add to these efforts. Together, they will generate the kinds of observations needed to search for the signatures described in the study.

Possible candidates for these future observations have already been identified. In 2024, Project Hephaistos identified seven potential Dyson sphere candidates among about 5 million cataloged stars, all linked to red dwarfs. One was ruled out after it was shown that a background black hole caused the observed signal. Several candidate Dyson sphere systems still remain under investigation. Amiri does not claim that any of these are actual Dyson spheres, and the paper makes this clear. Instead, the study offers a better way to tell true anomalies apart from dusty disks before using valuable telescope time. If a Dyson swarm surrounds a star and reradiates its energy at temperatures unlike those of natural stars, upcoming infrared surveys may finally be able to detect one.

Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.