Deciphering the Cosmic Formula for Planet Creation

Significant quantities of water vapor have been detected by scientists in the disc surrounding the young star HL Tauri, indicating the presence of water in areas where planets are forming. This discovery, made possible by the ALMA telescope in Chile, is the first time that astronomers have been able to measure water vapor in a cool, stable disc conducive to planet formation. Such findings might greatly enhance our knowledge of how life-supporting planets are formed. (See artist's concept.) Credit: SciTechDaily.com

In a disc around a young star, scientists have identified water vapor exactly where planets might be in the process of forming.

Water, which is crucial for life on Earth and is believed to have a significant part in planet formation, has never been mapped out in a stable, cool disc until now - the ideal type of disc for forming planets around stars.

For the first time, astronomers have been able to measure the amount of water vapor in the vicinity of a planet-forming star.

This research was made possible by the Atacama Large Millimeter/submillimeter Array (ALMA), a group of telescopes in the Chilean Atacama Desert. The UK ALMA Regional Centre Node (UK ARC), which provides support to the UK astronomers using ALMA, is hosted by The University of Manchester’s Jodrell Bank Centre for Astrophysics.

Dr. Anita Richards, a Senior Visiting Fellow at The University of Manchester and a former UK ARC member, played a crucial role in confirming that the 'Band 5' receiver system was working correctly, which was vital for ALMA to generate a detailed image of the water.

Dr. Richards commented, "To directly measure the amount of water vapor in areas where planets are forming brings us one step closer to understanding how easy it could be to produce worlds with oceans. This kind of observation requires the driest possible conditions and the ALMA array in Chile was the only one capable of producing such detailed information."

In the disc surrounding a young star, astronomers have identified water vapor exactly where planets may be in the process of forming. A detailed image of the water vapor appears in shades of blue in this photograph from the Atacama Large Millimeter/submillimeter Array (ALMA). The gas is brighter in the middle of the disc, closer to the young star, where temperatures are higher. The previous ALMA observations showing the dust distribution around the star appear as red rings. Credit: ALMA (ESO/NAOJ/NRAO)/S. Facchini et al.

The research, published in the journal Nature Astronomy, reveals three times more water than in all of Earth's oceans in the inner disc of the young, Sun-like star HL Tauri, located 450 light-years away from Earth in the Taurus constellation.

Stefano Facchini, an astronomer at the University of Milan, Italy, who led the study, stated, "I had never imagined that we could capture an image of oceans of water vapor in the same region where a planet is likely forming."

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 at a kilometer distance, enable astronomers to determine the distribution of water in different regions of the disc.

A significant amount of water was found in the region where a known gap in the HL Tauri disc exists – a place where a planet could potentially be forming. Young planet-like bodies orbiting and accumulating material carve out radial gaps in gas- and dust-rich discs, increasing their size. This suggests that this water vapor could affect the chemical composition of planets forming in those regions.

However, observing water with a ground-based telescope is a challenging task as the abundant water vapor in Earth’s atmosphere degrades the astronomical signals.

ALMA, operated by the European Southern Observatory (ESO) in collaboration with its international partners, is located at an elevation of about 5000 meters in a high and dry environment specifically to minimize this degradation, providing exceptional conditions for observation. To date, ALMA is the only facility able to map the distribution of water in a cool planet-forming disc.

The dust particles that make up a disc are the starting points of planet formation, colliding and aggregating into increasingly larger bodies orbiting the star. Astronomers believe that where it is cold enough for water to freeze onto dust particles, things stick together more efficiently — a perfect spot for planet formation.

Members of the UK ARC are contributing to a major upgrade of ALMA, which with ESO’s Extremely Large Telescope (ELT) also coming online within the decade, will provide even clearer views of planet formation and the role water plays in it. In particular, METIS, the Mid-infrared ELT Imager and Spectrograph, will give astronomers unrivaled views of the inner regions of planet-forming discs, where planets like Earth form.