Researchers have found water vapour in the disk around a young star where planet formation can occur.
Water is essential for life on Earth and is thought to play a significant role in planet formation.
However, until now, astronomers have never been able to map how water is distributed in a stable, cool disc. This type of disc offers the most favourable conditions for planets to form around stars.
Now, astronomers have weighed the amount of water vapour around a typical planet-forming star for the first time.
The findings were made possible thanks to the Atacama Large Millimeter/submillimeter Array (ALMA) – a collection of telescopes in the Chilean Atacama Desert.
Dr Anita Richards, Senior Visiting Fellow at The University of Manchester and previously a member of the UK ARC, said: “Directly measuring the amount of water vapour where planets are forming takes us a step closer to understanding how easy it could be to make worlds with oceans – how much water is attached to the agglomerating rocks, or is it mostly added later to an almost-fully-formed planet?
“This sort of observation needs the driest possible conditions and could only be made in such detail using the ALMA array in Chile.”
Water in the inner disk of stars
The researchers observed at least three times as much water as in all of Earth’s oceans in the inner disc of the young Sun-like star HL Tauri. This is located 450 lightyears away from Earth in the constellation Taurus.
Stefano Facchini, an astronomer at the University of Milan, Italy, who led the study, said: “I had never imagined that we could capture an image of oceans of water vapour 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 vapour at a distance of 450 lightyears from us.”
Water vapour could affect planet formation
The observations allow astronomers to determine the distribution of water in different regions of the disc.
A significant amount of water was found in a gap in the HL Tauri disc – a place where planet formation could occur.
Radial gaps are carved out in gas and dust-rich discs by orbiting young-plant like bodies as they gather material and grow. This observation indicates that water vapour could affect the chemical composition of planets forming in those regions.
The dust grains that comprise a disc are the seeds of planet formation, colliding and clumping into even larger bodies orbiting the star.
Astronomers believe that where is it cold enough for water to freeze onto dust particles, things stick together more efficiently – making it the ideal spot for planet formation.
ALMA’s unique capabilities
Observing water with a ground-based telescope is challenging as the abundant water vapour in Earth’s atmosphere degrades the astronomical signals.
Operated by European Southern Observatory, ALMA sits at around 5,000 metres elevation and is built in a high and dry environment to minimise this degradation.
To date, ALMA is the only facility able to map the distribution of water in a cool planet-forming disc.
Members of the UK ARC are contributing to a major ALMA upgrade, which will provide even clearer views of planet formation and the role water plays in it, in the future.
