Free Astronomy Magazine September-October 2025

32 ASTRO PUBLISHING gests the possible coevolution of stars and planets in a gas and dust rich environment, providing an im- portant clue to understanding the process of planet formation. Identifying the formation period of planetary systems, such as our Solar System, could be the beginning of the journey to discover the origin of life. The key to this is the unique sub- structures found in protoplanetary disks – the sites of planet formation. A protoplanetary disk is composed of low-temperature molecular gas and dust, surrounding a protostar. If a planet exists in the disk, its gravity will gather or eject materials within the disk, forming characteristic sub- structures such as rings or spirals. In other words, various disk substruc- tures can be interpreted as “mes- sages” from the forming planets. To study these substructures in detail, high-resolution radio observations with ALMA are required. Numerous ALMA observations of protoplanetary disks (or circumstellar disks) have been conducted so far. In particular, two ALMA large pro- grams, DSHARP and eDisk, have re- vealed the detailed distribution of dust in protoplanetary disks through high-resolution observations. The DSHARP project discovered that distinctive structures are common in circumstellar disks around 20 young stars, each exceeding one million years since the onset of star forma- tion. On the other hand, fewer dis- tinctive structures were found by the eDisk project that investigated disks around 19 protostars in the accretion phase (the stage where mass accre- tion onto the star and the disk is ac- tive). This phase occurs approxi- mately 10,000 to 100,000 years after star birth. This suggests that disks have diverse characteristics depend- ing on the age of the star. Here, the question is when do substructures, the signs of planet formation, ap- pear in disks. To find the answer, it is necessary to observe disks of a wide range of intermediate ages that have yet to be explored. However, limitations on the number of disks observable at high resolution, due to distance and observational time, make it challenging to conduct a statistically significant survey with a sufficiently large sample size. To overcome these limitations, the research team turned to super-reso- T he Nordic ALMA Regional Centre node, based at Onsala Space Observatory, provides full user support for ALMA users in the Nordic (Denmark, Finland, Iceland, Norway, Sweden) and Baltic (Lithuania, Latvia, Estonia) countries. [ESO/S. Guisard]