Shrouded by a swirl of gas and dust, a planetary gas giant roughly three to ten times the size of Jupiter has been discovered orbiting the young star MP Mus, previously thought to be a solitary body within an exoplanet-forming cloud.
The latest exoplanet discovery, led by a team from the University of Cambridge, used data from the Atacama Large Millimeter/submillimeter Array (ALMA) and the European Space Agency’s Gaia mission. Researchers from Germany, Chile, and France collaborated with the Cambridge team to refine their observations and uncover the hidden planet.
Observing the Early Universe and Protoplanetary Disks
The cloud of gas and dust surrounding MP Mus is a protoplanetary disk—the raw material from which planets form. Shaped like an enormous pancake, the gas, dust, and ice orbiting the young star gradually congeal into planets and asteroids through a gravitational process known as core accretion. As this process continues, the particles clump together, leaving behind gaps in the disk where material has been used up.
With increasingly powerful instruments, astronomers can now observe galaxies and star systems at much earlier stages of development than our own. These distant snapshots provide crucial clues about cosmic evolution, allowing scientists to link different phases of stellar and planetary development into a broader narrative.
One major challenge in studying the early stages of planet formation is that the particles in protoplanetary disks act as a veil, obscuring what lies within. Until now, Gaia had never detected a fully formed planet within such a disk, and this marks only the third discovery of its kind by any space mission.
A Not So Unremarkable Disk After All
“We first observed this star at the time when we learned that most disks have rings and gaps, and I was hoping to find features around MP Mus that could hint at the presence of a planet or planets,” said lead author Dr Álvaro Ribas from Cambridge’s Institute of Astronomy.
Initially, using only ALMA, Dr. Ribas believed the young star lacked any exoplanets. ALMA’s early data showed a flat, featureless disk with no gaps typically carved out by forming planets. However, given the star’s age—between seven and ten million years, well into the expected window for planet formation—the team suspected there might be more to uncover.
Taking a second look, Ribas and his colleagues again turned to ALMA, this time focusing on a longer 3 mm wavelength capable of penetrating deeper into the disk. This second round of observations revealed three distinct gaps: one close to the star, and two nearer to the disk’s edge.
Another Piece of the Exoplanet Puzzle
Ribas and his team weren’t the only ones intrigued by MP Mus. Miguel Vioque, a researcher at the European Southern Observatory, noticed an unusual wobble in the star’s motion after analyzing Gaia data.
“My first reaction was that I must have made a mistake in my calculations, because MP Mus was known to have a featureless disc,” said Vioque. “I was revising my calculations when I saw Álvaro give a talk presenting preliminary results of a newly-discovered inner cavity in the disc, which meant the wobbling I was detecting was real and had a good chance of being caused by a forming planet.”
By combining Gaia and ALMA data and running computer simulations, the team identified a gas giant—larger than Jupiter—as the cause of the star’s wobble. The exoplanet orbits its star at a distance between one and three times that of Earth’s orbit from the Sun.
“Our modelling work showed that if you put a giant planet inside the new-found cavity, you can also explain the Gaia signal,” said Ribas. “And using the longer ALMA wavelengths allowed us to see structures we couldn’t see before.”
Future Exoplanet Research
The discovery is important for future exoplanet and protoplanetary disk research, as it is the first time such a method has been used to detect an exoplanet. This indirect discovery technique can now be applied to data on other disks in the future, filling in our understanding of these early-stage star systems.
“We think this might be one of the reasons why it’s hard to detect young planets in protoplanetary discs, because in this case, we needed the ALMA and Gaia data together,” said Ribas. “The longer ALMA wavelength is incredibly useful, but to observe at this wavelength requires more time on the telescope.”
The breakthrough comes at a promising time: ALMA is slated for upgrades, and the upcoming Next Generation Very Large Array will further enhance astronomers’ ability to study young star systems in detail. Together with this new detection method, these tools could provide key insights into how our solar system—and others—came to be.
The paper, “A Young Gas Giant and Hidden Substructures in a Protoplanetary Disc,” appeared on July 14, 2025, in Nature Astronomy.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.