William Hubbard

Professor Emeritus

Ph.D., 1967, Berkeley

Years with LPL: 1972 to present

Exoplanets; Planetary Formation and Evolution, Planetary Atmospheres, Theoretical Astrophysics, Titan & Outer Solar System, Planetary interiors

Dr. Hubbard's research focuses on studies of the structure and evolution of Jupiter, Saturn, and extrasolar giant planets (EGPs). Originally as a Co-Investigator with the proposed INSIDE Jupiter orbiter and now as a Juno Co-Investigator, he showed how high-precision gravity data from a close-range Jupiter orbiter can be used to determine the depths to which Jupiter's extraordinary zonal wind patterns penetrate. Hubbard contributed to the 2013-2022 Planetary Sciences Decadal Survey of the US National Research Council as a member of the Giant Planet Panel. He is a Fellow of the American Astronomical Society, the American Geophysical Union, and the American Association for the Advancement of Science. He was awarded the 2005 Gerard P. Kuiper Prize in Planetary Sciences by the Division for Planetary Sciences of the American Astronomical Society. In collaboration with Burkhard Militzer at UC Berkeley, Hubbard is incorporating Militzer's first-principles density-functional equations of state for hydrogen-helium mixtures in models of Jupiter, Saturn, and EGPs. The models are matched to measurements of heat flow, mass, radius, and high-order gravity field (where known). One of the main objectives of the research is a determination of the metallicity of Jupiter and a validation of the standard cooling theory that is applied to EGPs.

In collaboration with the late Adam Showman (LPL) and Yohai Kaspi (Weizmann Inst.), Hubbard analyzed the signature of interior dynamics on Jupiter's high-order gravity field.  Hubbard is currently collaborating with Militzer, Jack Wisdom at MIT, and others to determine precise constraints on the moments of inertia of Jupiter and Saturn and implications for possible orbital resonances with Uranus and Neptune.

The above projects are a component of Hubbard's research related to his role as a Co-Investigator on the Juno spacecraft, orbiting Jupiter since 2016 and now in an extended mission..