天体観測で探る惑星形成の初期条件(<特集>アストロバイオロジー)

概要

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Characterizing extra-solar planetary systems is one of the most important research topics in contemporary astronomy. Today, more than 550 planets are known to exist, many of which show quite different characteristics from the Solar system planets in their masses, orbits, and densities. The situation makes us to recognize that it is central to construct the generic model on planet formation and evolution to reproduce the variety of exoplanets, and to place our Solar system in the context of other planetary systems. The key ingredients for the model are physical and chemical properties of protoplanetary disks, rotating structures around young stars where planets form. Although we are still far from being able to understand them, the astronomical observations have provided fundamental knowledge about such as masses, lifetimes, and structural evolution of disks. State-of-the-art instruments allow to directly explore close neighborhoods of the central stars, revealing rich diversity in their structures and signs of planets embedded in disks. In this paper, recent observational efforts of young circumstellar disks are reviewed focusing on infrared photometric and imaging studies.