James Imamura: The Formation of Planetary Systems

A fundamental question in astronomy, first posed in ancient times, is that of the origin of the Solar System. Today it is accepted that the collapse of dense cores in giant molecular clouds leads to the formation of stars.

In most proposed scenarios, the cores do not collapse directly to form stars, they first pass through an intermediate phase where a nascent star forms surrounded by a circumstellar disk because of the large specific angular momentum of the cloud.

The formation of stars and planetary systems results after mass and angular momentum are redistributed within these massive disks. This basic scenario had its origins in the 18th century when Kant (1755) and Laplace (1796) proposed, without direct observational support, the Nebular theory for the formation of the Solar System wherein planets formed from circumstellar material in orbit about the young Sun. Today, although aspects of the process remain elusive, Kant's and Laplace's original vision has been firmly established.

The paradigm that planets form in massive circumstellar disks is well-established. The mechanism, however, by which Jupiter-like planets are produced is not settled. It is currently thought that Jupiter-like planets form through either: (i) the core-accretion scenario where planet growth starts from the coalescence of small particulate matter in the disk and concludes with the gravitational capture of gas from the disk; and/or (ii) direct gravitational collapse driven by disk instabilities to form Jupiter-like planets. No singular piece of evidence establishes which theory offers the most plausible mechanism for the formation of Jovian planets.

In my talk, I will review observations of planets and planet forming regions, and the current state of modeling of planet formation mechanisms.