Unlock the cosmic recipe for planet formation

Researchers have discovered significant amounts of water vapor in the disk around the young star HL Tauri, suggesting the presence of water where planets form. This breakthrough, made possible by the ALMA telescope in Chile, marks the first time that astronomers have succeeded in quantifying water vapor in a cool, stable disk suitable for planet formation. The findings could have profound implications for our understanding of how planets form, particularly those capable of supporting life. (Artist’s concept.) Credit: SciTechDaily.com

Researchers have discovered water vapor in the disk around a young star, exactly where planets could form.

Water is a key ingredient of life on Earth and is also thought to play an important role in the formation of planets. Yet until now, astronomers have never been able to map how water is distributed in a stable, cold disk – the type of disk that provides the most favorable conditions for planets to form around it. stars.

Breakthrough in astronomical observation

For the first time, astronomers have measured the amount of water vapor around a typical planet-forming star.

The new discoveries were made possible thanks to the Atacama Large Millimeter/submillimeter network (ALMA) — a collection of telescopes in the Chilean Atacama Desert. The Jodrell Bank Center for Astrophysics at the University of Manchester hosts the UK ALMA Regional Center (UK ARC) node which supports UK astronomers using ALMA.

Dr Anita Richards, Visiting Principal Investigator at the University of Manchester and previously a member of the UK ARC, played a key role in the group verifying the operation of the ‘Band 5’ reception system, which was essential for ALMA to be able to produce detailed image of water.

Dr Richards said: “Directly measuring the amount of water vapor where planets form takes us closer to understanding how easy it might be to create worlds with oceans – how much water is attached to agglomerated rocks, or is it mainly added. later on an almost fully formed planet? This type of observation requires the driest conditions possible and can only be done in such detail using the ALMA network in Chile.

Water in the HL Tauri disc

Astronomers have discovered water vapor in a disk around a young star, exactly where planets could form. In this image, new observations from the Atacama Large Millimeter/submillimeter Array (ALMA), of which ESO is a partner, show water vapor in shades of blue. Near the center of the disk, where the young star lives, the environment is hotter and the gas brighter. The red colored rings are previous ALMA observations showing the distribution of dust around the star. Credit: ALMA (ESO/NAOJ/NRAO)/S. Facchini et al.

Results from the HL Tauri star system

The observations, published in the journal Natural astronomyreveal at least three times more water than in 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 Taurus.

Stefano Facchini, an astronomer at the University of Milan, Italy, who led the study, said: “I never imagined that we could capture an image of oceans of water vapor in the same region where a planet is likely to form. »

Co-author Leonardo Testi, an astronomer at the University of Bologna, Italy, added: “It is truly remarkable that we can not only detect but also capture detailed images and spatially resolve water vapor at a distance of 450 light years from us. »

These observations with ALMA, which show details as small as a human hair from a kilometer away, allow astronomers to determine the distribution of water in different regions of the disk.

Implications for planet formation

A significant amount of water was found in the region where a known gap exists in the HL Tauri disk – a place where a planet could potentially form. Radial gaps are carved out of gas- and dust-rich disks by the young orbiting planet-like bodies as they gather material and grow. This suggests that this water vapor could affect the chemical composition of planets forming in these regions.

But observing water with a ground-based telescope is no easy feat, because the abundance of water vapor in Earth’s atmosphere degrades astronomical signals.

ALMA, operated by the European Southern Observatory (THAT), with its international partners, is located at approximately 5,000 meters above sea level and is built in a high, dry environment specifically to minimize this degradation, providing exceptional observing conditions. To date, ALMA is the only facility capable of mapping the distribution of water in a cold planet-forming disk.

The dust grains that make up a disk are the seeds of planet formation, colliding and sticking together into ever-larger bodies orbiting the star. Astronomers think that where it’s cold enough for water to freeze on dust particles, the elements stick together more effectively – an ideal place for planets to form.

UK ARC members are contributing to a major upgrade to ALMA which, with the commissioning of ESO’s Extremely Large Telescope (ELT) later this decade, will provide even clearer views of planet formation and the role that water plays in it. In particular, METIS, the ELT Mid-Infrared Imager and Spectrograph, will provide astronomers with unparalleled views of the interior regions of planet-forming disks, where planets like Earth form.

Reference: “Resolved ALMA observations of water in the inner astronomical units of the HL Tau disk” by Stefano Facchini, Leonardo Testi, Elizabeth Humphreys, Mathieu Vander Donckt, Andrea Isella, Ramon Wrzosek, Alain Baudry, Malcom D. Gray, Anita MS Richards and Wouter Vlemmings, February 29, 2024, Natural astronomy.
DOI: 10.1038/s41550-024-02207-w

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