Oceans Of Water Vapor Found In Planet-Forming Disc Around Young Star

For the first time ever, astronomers have been able to map the distribution of water vapor in the disc surrounding a young star, a region where planets are believed to be forming. This discovery, made using the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, could provide significant insights into the role of water in planet formation and the origins of life as we know it.

The young star in question, HL Tauri, is located 450 light-years away in the constellation Taurus and is similar to our own Sun. The findings revealed an astonishing quantity of water vapor, at least three times as much as all of Earth’s oceans combined, in the star’s inner disc.

This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope
This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. (Credit: ALMA (ESO/NAOJ/NRAO))

“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,” says study lead author Stefano Facchini, an astronomer at the University of Milan, in a media release.

The observations conducted with ALMA mark the first time scientists have been able to see how water is distributed in a stable, cool disc — the environment most conducive to planet formation. This achievement is particularly significant given the challenges of observing water with ground-based telescopes due to the interference caused by Earth’s own atmospheric water vapor. ALMA’s location in the Chilean Atacama Desert at an elevation of about 5,000 meters, chosen for its dry conditions, minimizes this degradation and provides exceptional observing conditions.

“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 ,” notes study co-author Leonardo Testi, an astronomer at the University of Bologna.

The discovery was made in a region of the HL Tauri disc known to have a gap, which is thought to be carved out by orbiting young planet-like bodies as they accumulate material and grow. This finding suggests that the water vapor could play a crucial role in the chemical composition of planets forming within these gaps.

The presence of water in planet-forming discs is significant because it is a key ingredient for life on Earth and is thought to enhance the process of planet formation. When it is cold enough for water to freeze onto dust particles in the disc, these icy grains can stick together more efficiently, creating ideal conditions for planet formation.

“It is truly exciting to directly witness, in a picture, water molecules being released from icy dust particles,” says study co-author Elizabeth Humphreys, an astronomer at ESO.

This image shows the region in which HL Tauri is situated
This image shows the region in which HL Tauri is situated. HL Tauri is part of one of the closest star-forming regions to Earth and there are many young stars, as well as clouds of dust, in its vicinity. This picture was created from images forming part of the Digitized Sky Survey 2. (Credit: ESO/Digitized Sky Survey 2)

The study’s findings not only shed light on the process of planet formation but also hint at the potential for water to influence the development of planetary systems in a manner similar to its role in our own Solar System 4.5 billion years ago. With upcoming upgrades to ALMA and the anticipated launch of ESO’s Extremely Large Telescope (ELT), astronomers are poised to gain even deeper insights into planet formation and the pivotal role of water in this process. The ELT’s Mid-infrared ELT Imager and Spectrograph (METIS) will offer unparalleled views of the inner regions of planet-forming discs, where Earth-like planets emerge.

The study is published in the journal Nature Astronomy.


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