Six billion tonnes a second: Rogue planet found growing at record rate

Groundbreaking research from the University of St Andrews has revealed a dramatic ‘growth spurt’ in a mysterious rogue planet, a rare type of planet that drifts freely through space, untethered to any star. Unlike the planets in our solar system, rogue planets travel alone, making this discovery a significant leap in our understanding of planetary evolution beyond traditional star systems. 

Published today (Thursday 2nd October) in The Astrophysical Journal Letters, the new observations, made by an international team using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), reveal that this free-floating planet is eating up gas and dust from its surroundings at a rate of six billion tonnes a second.  

This is the strongest growth rate ever recorded for a rogue planet, or a planet of any kind, providing valuable insights into how they form and grow. 

The newly studied object, which has a mass five to 10 times that of Jupiter, is located about 620 light-years away in the constellation Chamaeleon. Officially named Cha 1107-7626, this rogue planet is still forming and is fed by a surrounding disc of gas and dust. This material constantly falls onto the free-floating planet, a process known as accretion. However, the team, which is comprised of nine research institutions throughout Europe, has now found that the rate at which the young planet is accreting is not steady. 

By August 2025, the planet was accreting about eight times faster than just a few months before, at a rate of six billion tonnes per second.  

The discovery was made with the X-shooter spectrograph on ESO’s VLT, located in Chile’s Atacama Desert. The team also used data from the James Webb Space Telescope, operated by the US, European and Canadian space agencies, and archival data from the SINFONI spectrograph on ESO's VLT. 

Professor Aleks Scholz from the School of Physics and Astronomy at St Andrews, and co-author of the study, said: "The origin of rogue planets remains an open question: are they the lowest-mass objects formed like stars, or giant planets ejected from their birth systems?”  

The findings indicate that at least some rogue planets may share a similar formation path to stars since similar bursts of accretion have been spotted in young stars before.  

As co-author Dr Belinda Damian, also an astronomer at the University of St Andrews, added: “This discovery blurs the line between stars and planets and gives us a sneak peek into the earliest formation periods of rogue planets.” 

By comparing the light emitted before and during the burst, astronomers gathered clues about the nature of the accretion process. Remarkably, magnetic activity appears to have played a role in driving the dramatic infall of mass, something that has only been observed in stars before. This suggests that even low-mass objects can possess strong magnetic fields capable of powering such accretion events. The team also found that the chemistry of the disc around the planet changed during the accretion episode, with water vapour being detected during it but not before. This phenomenon had been spotted in stars but never in a planet of any kind. 

Free-floating planets are difficult to detect, as they are very faint, but ESO’s upcoming Extremely Large Telescope (ELT), operating under the world's darkest skies for astronomy, could change that. Its powerful instruments and giant main mirror will enable astronomers to uncover and study more of these lonely planets, helping them to better understand how star-like they are.