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News — A team of international astronomers have embarked on an exciting new project to hunt for planets forming around young stars. The exoALMA project, using the powerful Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, is peering into the dusty disks where planets are born. Thanks to newly developed advanced imaging techniques, exoALMA has revealed the most exquisite images of young solar systems, never before seen by astronomers. This research project involved 17 papers published in a special issue of the Astrophysical Journal of Letters, with several more coming this summer. ALMA is supported in part by the U.S. National Science Foundation through the NSF National Radio Astronomy Observatory (NSF NRAO).

"The new approaches we’ve developed to gather this data and images are like switching from reading glasses to high-powered binoculars—they reveal a whole new level of detail in these planet-forming systems," said Richard Teague, PI of the exoALMA project. "We're seeing evidence of hugely perturbed and dynamic disks, highly suggestive of young planets shaping the disks they're born in." The team targeted 15 young star systems to map the motions of the gas in detail in order to uncover the processes that form planetary systems, and, in certain cases, identify the telltale signs of infant planets, including gaps and rings in the dust disks around stars, swirling motions in the gas caused by a planet's gravity, and physical changes in the disk that might signal a planet's presence. 

Unlike traditional planet-hunting methods that look for a young planet's direct light, exoALMA is searching for the effects planets have on their surroundings. This approach allows astronomers to potentially detect much younger planets than ever before. "It's like trying to spot a fish by looking for ripples in a pond, rather than trying to see the fish itself," adds Christophe Pinte, an astrophysicist at the Institute of Astrophysics and Planetology of Grenoble, Monash University, and co-PI of the exoALMA team.

The team emphasized the technical challenges involved in processing the massive amounts of data to produce such sharp images. “We developed new techniques to precisely align observations taken at different times and remove unwanted noise and distortions,” explained Dr. Ryan Loomis, a scientist with the U.S. National Science Foundation National Radio Astronomy Observatory, who led the data processing publication, “We had to carefully combine and clean up the data to reveal all the subtle details." 

These new calibration approaches and the development of tailored data-processing and analysis techniques from the exoALMA project will improve astronomers' ability to map out the planet formation process in several key ways.

• Higher resolution and sensitivity: The observations provide an unprecedented combination of high angular (100 mas, or 14 au at the typical distances of the sources) and spectral (26 m/s) resolution data of gas emission from protoplanetary disks, allowing astronomers to detect subtle structures and motions that reveal key processes of planet formation.
• Multiple molecular tracers: By observing 12CO, 13CO, and CS emission simultaneously, astronomers can probe different vertical layers and physical conditions within the disks.
• Improved imaging and calibration techniques: The careful alignment, self-calibration, and imaging procedures developed allow for higher fidelity images with fewer artifacts, enabling more confident detection of real disk features.
• Development and validation of numerical and analytical methods: The refinement of new analysis techniques alongside comprehensive benchmarking efforts ensure all information is accurately extracted from the data while simulations offer robust predictions to be tested. 

By leveraging these newly developed techniques and the exquisite dataset, the exoALMA team managed to map the density, temperature, and velocity structure of planet-forming disks in unprecedented detail. “This large program allowed for a systematic study of the 3-dimensional structure of many of these disks, providing key insights into the physical properties of the planet formation environment,” says Myriam Benisty, of the Max Planck Institute for Astronomy in Heidelberg, and co-PI of the exoALMA team. “Another exciting part of this research is that most of this work was done by researchers early in their career, who wrote 12 out of 17 of our papers,” adds Misato Fukagawa, of the National Astronomical Observatory of Japan, and co-PI of the program.

Among the most prominent results of this first release of the exoALMA program, the research team shedded light on several open questions connected to how planets form:

• The survey unambiguously demonstrated that protoplanetary disks are highly dynamic environments which exhibit a striking level of structure in their gas distributions, rivaling that of the dust counterparts.
• The extraction of rotational velocity profiles, typically achieving a precision of 10 m/s, revealed subtle departures from Keplerian rotation, indicating that pressure modulations in the disk drive the shepherding of large dust grains into the rings seen in all disks.
• Similarly to what has been achieved with the rotation curves of full galaxies to measure the mass of dark matter halos, the team managed to estimate the gravitational influence of the disk itself allowing for a novel approach to determining the mass available for forming planets, benchmarking alternative methods leveraging line fluxes.
• exoALMA provides the first insights into the key physical mechanisms at play during the earliest stages of the formation of solar system analogues by revealing dynamical interactions with companions or planets, as well as complex instabilities.

“It is through this joint analysis of the gas and dust which is shedding light on the processes which are active within a protoplanetary disk and which may be responsible for exciting the structure so commonly observed,” comments Stefano Facchini, co-PI of exoALMA based at the University of Milan.

Looking ahead, the exoALMA project promises to revolutionize scientists' understanding of how planets interact with their natal environments, and tackle the challenge of highly asymmetric sources, as revealed by the complex 2-dimensional kinematical pattern in these disks. The first exoALMA findings are published in a series of papers in The Astrophysical Journal Letters. All of the data and images will be made publicly available to support further scientific discoveries.

About NRAO

The National Radio Astronomy Observatory (NRAO) is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

About ALMA

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.