Astronomers produce the first complete picture of (gas) planet formation in action
To the point
First image of its kind: Astronomers have directly imaged the “swirl” where a protoplanet interacts with the gas in the surrounding protoplanetary disk.
Fine details as a challenge: Taking an image of structures this small requires a powerful observatory like ALMA but also the advanced analytical skill to extract every last piece of information from ALMA observational data.
First complete image: This is the first planet where we have images of all the parts of planet formation: a planet that is still growing (“accreting”), the protoplanetary disk, and the “swirl” interaction.
Interpreting swirling gas: Swirls in the gas of protoplanetary disks had been detected before. Observations like this new result could help tell when such a swirl indicates the presence of a planet.
Over the past decades, astronomers have reconstructed a fairly complete scenario for planet formation, from minute dust motes clumping together to the emergence of rocky spheres thousands of kilometers across like our Earth, or larger gas giants like Jupiter. Key elements of that scenario are anchored in simulations and measurements, but direct observations (“can’t we just watch how planets form?”) have been notoriously absent. Now, a team of astronomers led by Myriam Benisty at the Max Planck Institute for Astronomy has captured a unique new image of planet formation in action: Taken with the ALMA observatory in Chile, the image shows the interactions of the planet WISPIT 2b, a gas giant with five times the mass of Jupiter, with the surrounding gas of its birthplace.
Protoplanetary disks and their structures
Planets are born in protoplanetary disks consisting of gas and dust, which occur naturally around newly-formed stars. Planets form when dust within those disks clumps together. In a first step, the result is larger pebbles, which in turn clump further to form planetesimals a few to a hundred kilometers in size. Those planetesimals join up to form rocky, planet-size spheres. In a gas-rich part of the disk, such rocky spheres can collect large amounts of gas and become the cores of gas giants like Jupiter or Saturn.
Observational evidence for this scenario has mostly been indirect. It is only within the past decade or so that new facilities have provided astronomers with a more detailed look: In 2014, once the millimeter/submillimeter observatory ALMA had become fully operational, it delivered the first images of ring-like structures in protoplanetary disks, thought to be caused by the presence of young planets. In 2018, astronomers led by Miriam Keppler, then a PhD student at MPIA, used the SPHERE instrument at ESO’s Very Large Telescope to produce the first confirmed image of a protoplanet inside a protoplanetary disk, the planet PDS 70b within the disk surrounding the star PDS 70.
Introducing the WISPIT 2 system
At a distance of only about 370 light-years from us, the PDS 70 system is close enough to allow for detailed observations. What the system does not currently provide is a chance to study the interaction between a protoplanet and gas in its immediate surroundings. The planets of PDS 70 seem to have cleared their close neighbourhoods of gas rather effectively. Enter a new contender: the WISPIT 2 system, whose discovery was announced in August 2025, and which is only the second disk in which a protoplanet can clearly be discerned. WISPIT 2 is named after the search program that led to its discovery (“WIde Separation Planets In Time”). It is located at a distance of 430 light years from Earth.
The system’s first known planet, WISPIT 2b, a gas giant, was discovered in parallel with the SPHERE instrument at ESO’s VLT and the 6.5 m Magellan Clay telescope. The signature light of hot hydrogen (the “Hα line”) indicates that the planet is still accreting gas from its surroundings, growing ever more massive. The discovery of a second planet, WISPIT 2c, was announced in March 2026, based on observations with the VLT instruments SPHERE and GRAVITY+. In an additional twist, work by MPIA PhD student Cade Bürgy published in August 2026 shows that in the center of the disk, instead of a single star, there are two stars in very close orbit!
The challenge of fine details
A key challenge in exploring planet formation using astronomical images is the minute scale of the structures involved. If someone standing 2 meters away from you were to hold up a book, would you be able to read the text? How about 10 meters? At the distance of the WISPIT 2, imaging a structure as large as the Earth-Sun distance (“one astronomical unit”) is as difficult as reading an ordinary book over a distance of 5 kilometers.
When it comes to gas and dust in protoplanetary disks, there is really only one facility that can provide the desired level of detail: the ALMA observatory, a field of 66 radio dishes on the Chajnantor plateau in the Chilean Andes, operated by an international consortium of partners. ALMA’s antennas can be combined to be as sharp-sighted as a giant single telescope with a diameter of up to 16 kilometers. Once the discovery of WISPIT 2b was announced, using ALMA to look at its gas and dust was the logical next step.
Pointing ALMA to the Wispit 2 system
In September 2025, with the observatory in one of its most powerful configurations for detailed imaging, the ALMA antennas turned towards WISPIT 2b. Additional observations followed in November 2025 and March 2026. The observations had been planned and proposed by a team led by Stefano Facchini of the University of Milan and including Myriam Benisty, who is the director of the Planet Formation and Exoplanets (PFE) department at MPIA. Facchini, Benisty and a number of additional members of the team were uniquely positioned to take on the challenge: over the previous years, they have been part of the exoALMA project, honing their skills to extract the maximum amount of information from ALMA observations of protoplanetary disks. Incidentally, Benisty had also been part of the collaboration that discovered WISPIT 2b.
The combination of a powerful observatory with specific, highly-skilled analytical skills paid off: The team was able to take images of the dust and gas as detailed as any that had been taken of any protoplanetary disk before. Particularly rewarding was the effort to image the gas in the disk. Benisty, who led this part of the project, says: “We clearly see both planets shaping their environment. WISPIT 2c has carved a cavity, and WISPIT 2b a gap. Around WISPIT 2b, we find swirls of gas that had been predicted by simulations of disk-planet interactions, but never actually seen before. Now there is an image of them!” This makes WISPIT 2b the only protoplanet where we can see the protoplanetary disk, the planet, the evidence that the planet is still accreting, and now as the final piece of the puzzle, the gas interacting directly with the planet. Planet formation in action.
Putting the new discovery to work
Once the new result has been joined by other observations of its kind, it has the potential of resolving an important open question in the field. Swirls on their own, without the direct detection of a planet, have been seen in other protoplanetary disks before. Some researchers argue these swirls indicate the presence of an unseen planet. Others have pointed to turbulent processes in such disks that may explain features of this kind without the presence of a planet. The new observations are the first example for a system where we see both the swirling features and the associated planet. Stefano Facchini of the University of Milan, leader of the ALMA observation proposal that yielded the new results, says: “Hopefully, observations like this will teach astronomers to distinguish between disk features that indicate the presence of a protoplanet and features that don’t.”
The present result is about a gas giant at a considerable distance (57 au) from the central stars, almost twice as far as Neptune is from the Sun. Almost all of the known exoplanets are much closer to their central star than that. But the methods used in the analysis pave the way for observations with the next generation of instruments, namely at ESO’s 39 m Extremely Large Telescope and at the planned upgrade of the ALMA antennas with significantly improved sensitivity. In a bit over a decade, those tools could provide an updated version of the present result: an action picture of a gas giant at the same distance from its star as Jupiter or Saturn from the Sun – and hopefully, new insights about how such gas giants help shape a solar system like our own!
Background information
The results presented here have been published as M. Benisty et al., "Mapping the WISPIT 2 Planet-Hosting Cavity at Sub-Hill-Radius scales," in the journal Astrophysical Letters. The detection of the binary at the center of WISPIT 2 is accepted as an A&A letter, and available as an e-print on arXiv, as C. J. Bürgy et al., "A closer look at the WISPIT 2 host star. Evidence for a spectroscopic binary."
The MPIA researchers involved are Myriam Benisty, Francesco Zagaria and Cade Bürgy, in collaboration with Stefano Facchini (University of Milan), Richard Teague (MIT), Pietro Curone (University of Chile), Viviana Pezzotta (University of Milan), Jaehan Bae (University of Florida), Gabriele Cugno (University of Zurich) and Daniel Price (Monash University).
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
Myriam Benisty has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (PROTOPLANETS, grant agreement No. 101002188). Stefano Facchini acknowledges a financial contribution from the European Union (ERC, UNVEIL, 101076613). Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them.
