Free Astronomy Magazine May-June 2024

MAY-JUNE 2024 ASTRO PUBLISHING “Taking part in such an important discovery in the iconic HL Tauri disc was beyond what I had ever expected for my first research experience in as- tronomy,” adds Mathieu Vander Donckt from the University of Liège, Belgium, who was a master’s student when he participated in the research. A significant amount of water was found in the re- gion where a known gap in the HL Tauri disc exists. Ring-shaped gaps are carved out in gas- and dust- rich discs by orbiting young planet-like bodies as they gather up material and grow. “Our recent im- ages reveal a substantial quantity of water vapour at a range of distances from the star that include a gap where a planet could potentially be forming at the present time,” says Facchini. This suggests that this water vapour could affect the chemical composition of planets forming in those regions. Observing water with a ground-based telescope is no mean feat as the abundant water vapour in Earth’s atmosphere degrades the astronomical sig- nals. ALMA, operated by ESO together with its in- ternational partners, is an array of telescopes in the Chilean Atacama Desert at about 5000 metres elevation that was built in a high and dry environ- ment specifically to minimise this degradation, providing exceptional observing conditions. “To date, ALMA is the only facility able to spatially resolve water in a cool planet-forming disc,” says co-author Wouter Vlemmings, a professor at the Chalmers University of Technology in Sweden. “It is truly exciting to directly witness, in a picture, water molecules being released from icy dust par- ticles,” says Elizabeth Humphreys, an astronomer at ESO who also participated in the study. The dust grains that make up a disc are the seeds of planet formation, colliding and clumping into ever larger bodies orbiting the star. Astronomers believe that where it is cold enough for water to freeze onto dust particles, things stick together more effi- ciently — an ideal spot for planet formation. “Our results show how the presence of water may influ- ence the development of a planetary system, just like it did some 4.5 billion years ago in our own Solar System,” Facchini adds. With upgrades happening at ALMA and ESO’s Extremely Large Telescope (ELT) coming online within the decade, planet formation and the role water plays in it will become clearer than ever. In particular METIS, the Mid-infrared ELT Imager and Spectrograph, will give astronomers unrivalled views of the inner regions of planet-forming discs, where planets like Earth form. T his 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. [ALMA (ESO/NAOJ/NRAO)] A stronomers have found water vapour in a disc around a young star exactly where planets may be forming. In this image, the new observations from the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, show the water vapour in shades of blue. Near the centre of the disc, where the young star lives, the environment is hotter and the gas brighter. The red-hued rings are previous ALMA observations showing the distribution of dust around the star. [ALMA (ESO/NAOJ/NRAO)/S. Facchini et al.] !