New observational facilities are redefining our ideas on discs:
(1) ALMA/SPHERE are producing spectacular images of individual discs, revealing an amazing complexity in morphology. ALMA also opened the investigation of the physical, chemical and dynamical properties of gas: we can now routinely spatially resolve a wide variety of molecular species, that give us direct information on temperature gradient and surface density of the gas. At the same time, NIR high contrast can detect very young massive planets in the disc gaps and study their immediate environment.
Protoplanetary disks as observed by ALMA
(2) Another key aspect regards the spectroscopic characterisation of young stellar objects with protoplanetary discs, based on VLT-XShooter data (complemented by VLT-CRIRES and JWST) that we have and are acquiring. This analysis will provide information on the stellar and accretion properties, as well as on the properties of the winds and jets through forbidden line emission.
Hydrodynamical simulation of a disc torn into two disconnected rings by a central binary (left), synthetic ALMA dust continuum emission (middle), and synthetic scattered light infrared emission, with prominent shadows (right) - Facchini, Juhasz & Lodato (2018)