Astronomers have discovered a new relationship between water and planet formation

Water is an essential element for life on Earth, and is also thought to play an important role in planetary formation. But until now, it has never been possible to map how water is distributed in a stable, cool disk, the type of disk that provides the most favorable conditions for planets to form around stars. The new results are based on data from the Atacama Large Millimeter/submillimeter Array.

“I never thought we could image oceans of water vapor in the same region where a planet is likely to form,” says Stefano Facchini, an astronomer at the University of Milan in Italy, who led the study whose results were published today. . Observations show that the inner disk of the young, sun-like star HL Tauri, located 450 light-years away in the constellation Taurus, contains at least three times as much water as all of Earth's oceans combined.

“It is truly remarkable that we can not only detect water vapor, but we can also take detailed images 450 light-years away,” added co-author Leonardo Testi, an astronomer at the University of Bologna in Italy. ALMA observations allowed astronomers to measure the distribution of water in different parts of the disk around HL Tauri.

Separation

A large amount of water is found in the region where there is a toroidal void in the HL Tauri disk. Such a concentric “separation” in the disk of gas and dust is eroded by young planet-like objects orbiting the star, which collect and grow material.

“Our images show a large amount of water vapor at various distances from the star, including the void where a planet may be forming right now,” Facchini says. This suggests that this water vapor could affect the chemical composition of planets that form in regions like these.

Detecting water using a telescope on Earth is no easy task, because the large amount of water vapor in our planet's atmosphere disrupts the radiation that ALMA picks up. ALMA is an array of dozens of radio dishes at an altitude of about 5,000 meters in the Chilean Atacama Desert, deliberately placed in this high, dry location to reduce the effect of water vapor in the Earth's atmosphere. Currently, this is the only observing facility on Earth capable of distinguishing the signal from water in a cold planetary disk.

“It's really exciting to see an image of water molecules emitted from icy dust grains,” says Elizabeth Humphreys, an astronomer at the European Southern Observatory, who also worked on the study. Dust particles in the disk act as seeds for planetary formation. They collide and come together into larger and larger pieces that orbit the star. Astronomers believe that when it's cold enough for water to freeze into dust particles, everything sticks together better — an ideal environment for planet formation. “Our results show that the presence of water can influence the evolution of a planetary system, just as it did in our solar system about 4.5 billion years ago,” Facchini said.