Protoplanetary discs. Protoplanetary discs are compressed circles, spirals or ellipses of gas and dust, which form around protostars in the early stages of their development. Dust within a disc coalesces into planetesimals and the seeds of planets are formed. In these images the discs show concentric rings of gas, and gaps indicating planet formation. As planets form, they gravitationally interact with the disc and create various tell-tale features and structures. Studying young star systems as they form and evolve may help us to understand more about how our Solar System formed. Images obtained by the Atacama Large Millimeter/submillimeter Array (ALMA).