What Makes a Planet "Giant"?

This lecture by Prof. Dr. Ravit Helled from the Department of Astrophysics at the University of Zurich explores a new theory about giant planet formation. Discover a proposed pathway where runaway gas accretion begins only when planets reach approximately 100 Earth masses and occurs after several million years. Learn why this model suggests the transition to a gas giant—defined as a planet primarily composed of hydrogen and helium—occurs at around Saturn's mass. Understand how efficient heavy-element accretion creates enough energy to delay rapid gas accretion, potentially making Saturn a "failed giant planet." Examine how this theory explains the distinct characteristics of Jupiter, Saturn, Uranus, and Neptune, as well as observed patterns in exoplanet mass-radius relations, the relative scarcity of gas giants, and the high metallicity of intermediate-mass exoplanets.