Water vapor detected in planet-forming disk around a young star; This revealed the conditions that enable planet formation and the potential impact on planetary composition.

Researchers discovered water vapor in the disk around the young star, exactly where planets form. Water is an essential component for life on Earth and is also believed to have played an important role in the formation of the planet.

But until now we haven’t been able to map how water is distributed in a stable, cold disk (the type of disk around stars that provides optimal conditions for planet formation). The new discoveries were made possible by the Atacama Large Millimeter/submillimeter Array (ALMA) in partnership with the European Southern Observatory (ESO).

Magnificent observations from ALMA

“I never thought we could photograph oceans of water vapor in the region where a planet is likely to form,” said Stefano Faccini, an astronomer at Italy’s University of Milan who led the research published Feb. 29. inside astronomy of nature. Observations found at least three times more water than all of Earth’s oceans in the inner disk of the young sun-like star HL Tauri, located 450 light-years from Earth in the constellation Tauri.

“It’s really amazing that we can not only detect it, but also take detailed images and spatially resolve water vapor 450 light-years away,” adds co-author Leonardo Testi, an astronomer at the University of Bologna, Italy. ALMA’s “spatially resolved” observations allow astronomers to determine the distribution of water in different regions of the disk. “Participating in such an important discovery in the iconic HL Tauri disk was more than I expected from my first research experience in astronomy,” adds Mathieu Vander Donkt of the University of Liège, Belgium, who was a graduate student when he participated in the research.

The role of water in the formation of the planet

A significant amount of water was found in the region where the known gap is located in the HL Tauri disk. Annular cracks are formed in gas- and dust-saturated disks by young, rotating planetesimals as they accumulate material and grow. “Our latest images show significant amounts of water vapor at various distances from the star, including a gap where a planet could potentially form at this time,” says Facchini. This suggests that water vapor may affect the chemical composition of planets forming in these regions.

Observing water with a ground-based telescope is not an easy task because the large amount of water vapor in the Earth’s atmosphere degrades the quality of astronomical signals. ALMA, managed by ESO together with its international partners, is a telescope array located at an altitude of approximately 5,000 meters in Chile’s Atacama Desert, providing exceptional observing conditions and has been specially constructed in a high and dry environment to minimize this distortion. “ALMA is currently the only facility that can spatially resolve water in the cool planet-forming disk,” says co-author Wouter Vlemmings, a professor at Chalmers University of Technology in Sweden.

Implications for future research

“It is truly fascinating to see how water molecules are released from icy dust particles in the image,” says Elizabeth Humphreys, one of the ESO astronomers involved in the study. The dust grains that make up the disk are the seeds of planet formation, colliding and accumulating into increasingly larger bodies orbiting the star. Astronomers believe that objects stick together more effectively when it is cold enough for water to freeze on dust particles; This is an ideal place for planet formation. “Our results show how the presence of water can influence the evolution of the planetary system, as it did in our solar system about 4.5 billion years ago,” adds Facchini.

With upgrades at ALMA and ESO’s Extremely Large Telescope (ELT), which will operate for a decade, planet formation and the role of water on the planet will become clearer than ever. Specifically, METIS, the Mid-Infrared ELT Imager and Spectrograph, will provide astronomers with unique images of the inner regions of planet-forming disks where planets like Earth form.