Free Astronomy Magazine September-October 2023

19 SEPTEMBER-OCTOBER 2023 ASTRO PUBLISHING tending over distances bigger than the entire So-lar System. This finding then motivated as- tronomers to analyse archive obser- vations of the same system made with ALMA, in which ESO is a part- ner. The VLT observations probe the surface of the dusty material around the star, while ALMA can peer deeper into its structure. “With ALMA, it be- came apparent that the spiral arms are undergoing fragmentation, re- sulting in the formation of clumps with masses akin to those of plan- ets,” says Zurlo. Astronomers believe that giant plan- ets form either by ‘core accretion’, when dust grains come together, or by ‘gravitational instability’, when large fragments of the material around a star contract and collapse. While researchers have previously found evidence for the first of these scenarios, support for the latter has been scant. “No one had ever seen a real obser- vation of gravitational instability happening at planetary scales — until now,” says Philipp Weber, a researcher at the University of San- tiago, Chile, who led the study pub- lished in The Astrophysical Journal Letters . “Our group has been searching for signs of how planets form for over ten years, and we couldn’t be more thrilled about this incredible discov- ery,” says team-member Sebastián Pérez from the University of Santi- ago, Chile. ESO instruments will help as- tronomers unveil more details of this captivating planetary system in the making, and ESO’s Extremely Large Telescope (ELT) will play a key role. Currently under construction in Chile’s Atacama Desert, the ELT will be able to observe the system in greater detail than ever before, col- lecting crucial information about it. “The ELT will enable the exploration of the chemical complexity sur- rounding these clumps, helping us find out more about the composi- tion of the material from which potential planets are forming,” con- cludes Weber. O n the left hand side in yellow is an image of the young star V960 Mon and its surrounding dusty material, taken with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument installed on ESO’s Very Large Telescope (VLT). Light that is reflected off of the dusty material orbiting the star becomes polarised — meaning it oscillates in a well- defined direction rather than randomly — and is then detected by SPHERE, revealing mesmerising spiral arms. These findings motivated astronomers to analyse archival observations of the same system taken using Atacama Large Millimeter/submil- limeter Array (ALMA), in which ESO is a partner. The results of this analysis can be seen on the right hand side in blue. The wavelengths of light at which ALMA observes allow it to pierce deeper into the orbiting material, revealing that the spiral arms are fragmenting and forming clumps with masses similar to that of planets. These clumps could contract and collapse via a process known as “gravitational instability” to form giant planets. [ESO/ALMA (ESO/NAOJ/NRAO)/Weber et al.] !