Rogue planet caught behaving like a star in unprecedented observation

Astronomers have observed a planet that in some ways behaves more like a star — including a massive growth spurt unlike anything witnessed before in a free-floating planet.

The rogue planet, which does not orbit any star, is called Cha 1107-7626 and is outside of our solar system, 620 light-years from Earth in the Chamaeleon constellation. A single light-year, or the distance light travels in one year, is equal to 5.88 trillion miles (9.46 trillion kilometers).

The planet has a mass five to 10 times that of Jupiter, the largest planet in our solar system. And it’s getting bigger every second, according to new research published Thursday in The Astrophysical Journal Letters.

Estimated to be 1 million to 2 million years old, Cha 1107-7626 is still forming, said study coauthor Aleks Scholz, an astronomer at the University of St. Andrews in Scotland. It may sound old, but astronomically speaking, the planet is in its infancy. By contrast, the planets in our solar system are about 4.5 billion years old.

Cha 1107-7626 is surrounded by a disk of gas and dust, which constantly falls onto the planet and accumulates during a process that astronomers call accretion. But the rate at which the young planet is growing varies, the study authors said.

Observations with the European Southern Observatory’s Very Large Telescope in Chile’s Atacama Desert, along with follow-up views conducted by the James Webb Space Telescope, showed that the planet is adding material about eight times faster than a few months earlier and gobbling up gas and dust at a record rate of 6.6 billion tons (6 billion metric tons) per second.

The unusual burst of activity is the strongest growth rate ever recorded for a planet of any kind, said lead study author Víctor Almendros-Abad, an astronomer at the Palermo Astronomical Observatory of the National Institute for Astrophysics in Italy, and is shedding light on the tumultuous formation and evolution of planets.

“We’ve caught this newborn rogue planet in the act of gobbling up stuff at a furious pace,” said senior coauthor Ray Jayawardhana, provost and professor of physics and astronomy at Johns Hopkins University, in a statement.

“Monitoring its behavior over the past few months, with two of the most powerful telescopes on the ground and in space, we have captured a rare glimpse into the baby phase of isolated objects not much heftier than Jupiter. Their infancy appears to be much more tumultuous than we had realized.”

An unprecedented burst of growth

Astronomers first discovered Cha 1107-7626 in 2008, and since then, they have observed it with different telescopes to learn more about how the infant planet evolves, as well as to study its surroundings.

The research team observed the planet with Webb in 2024, making a clear detection of the surrounding disk. Next, the researchers studied it using the X-shooter spectrograph on the Very Large Telescope, which can capture different wavelengths of light emitted by an object ranging from ultraviolet to near-infrared.

The observations detected a puzzling event as the planet transitioned from a steady accretion rate in April and May to a burst of growth between June and August.

“I fully expected that this is a short-term event, because those are much more common,” Scholz said. “When the burst kept going through July and August, I was absolutely stunned.”

Follow-up observations made using the Webb telescope also showed that the chemistry of the disk had changed. Water vapor, present during the growth spurt, wasn’t in the disk before. Webb is the only telescope capable of capturing such detailed changes in the environment for such a faint object, Scholz said. Prior to this research, astronomers had only ever seen the chemistry of a disk change around a star, but not around a planet.

Comparing observations from before and during the event showed that magnetic activity seems to be the main driver behind how much gas and dust is falling on the planet — a phenomenon typically associated with stars as they grow.

But the new observations suggest that objects with much less mass than stars — the rogue world is less than 1% the mass of our sun — can have strong magnetic fields capable of driving the growth of the object, according to the study authors.

A planet that acts like a star

The origin of rogue planets remains murky. It’s possible they are planets that are kicked out of orbit around stars due to the gravitational influence of other objects. Or perhaps they are the lowest-mass objects that happen to form like stars. For Cha 1107-7626, astronomers said they think it’s the latter.

“This object most likely formed in a way similar to stars — from the collapse and fragmentation of a molecular cloud,” Scholz said.

A molecular cloud is a massive, cold cloud of gas and dust that can stretch for hundreds of light-years, according to NASA.

“We’re struck by quite how much the infancy of free-floating planetary-mass objects resembles that of stars like the Sun,” Jayawardhana said in a statement. “Our new findings underscore that similarity, and imply that some objects comparable to giant planets form the way stars do, from contracting clouds of gas and dust accompanied by disks of their own, and they go through growth episodes just like newborn stars.”

When comparing the new data with archival information, the team noted that the planet also experienced a high growth rate event observed in 2016, hinting at the idea that it may undergo recurring growth spurts. Now, the team wants to investigate how long the bursts last and how often they occur.

“From that we can find out how much they really contribute to the growth, or what is triggering strong accretion bursts,” Scholz said. “The fact that we see accretion bursts across such a wide range of (objects) must be telling us something — we are not quite sure yet what it is.”

Seeing behavior typically associated with the formation of stars in an isolated young planet is significant, said Dr. Jacco van Loon, an associate professor of astrophysics and director of the Keele Observatory at Keele University in England. He was not involved in the new research but noted that the wealth of observational detail revealed a rich molecular chemistry within the disk around the planet.

“Further research might clarify to what extent this differs from the disks around forming stars, but my curiosity focuses on what the composition might be of possible moons of this massive planet that might also form in this material,” van Loon said. “One can only think of Saturn’s moon Titan, which boasts an atmosphere and weather, to imagine what such moon might be like and whether it could eventually play host to life.”

The study also marks an important new step in understanding the accretion process of rogue planets, said Dr. Núria Miret Roig, assistant professor in the department of quantum physics and astrophysics at the University of Barcelona in Spain. Roig also was not involved in the new study.

“To deepen our understanding on the origin of these exotic celestial bodies,” Roig said, “it is essential to complement this type of work with studies on their abundance, atmospheric composition and the presence and properties of surrounding disks and companions.”

Rogue planets are incredibly dim and faint, making them difficult to detect. But new telescopes, such as the Vera C. Rubin Observatory, the upcoming Extremely Large Telescope, or ELT, in Chile and the Nancy Grace Roman Space Telescope, slated to launch in 2027, could change the way astronomers study these wandering worlds — and just how starlike they are.

“The ELT will be powerful enough to not only study these faint, free-floating planets in much more detail, but for example it will also be possible to look for close companions that might be responsible for triggering such bursts,” Almendros-Abad said.

“(Rubin will) catch these rare outbursts across the whole population of known young planetary-mass objects, giving us, for the first time, a statistical picture of how often they happen, and how long they last.”

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