Jonathan Fortney

He is a professor of astronomy and astrophysics at the University of California, Santa Cruz, where he leads the Other Worlds Laboratory (OWL). UCSC has long been a hub for exoplanet theory, and Fortney's group models planets ranging from super-Earths to gas giants.

He builds theoretical models that connect a planet's mass, radius, temperature, and age to its interior composition and to the spectra we can observe. His mass-radius models are widely used to interpret transiting planets discovered by missions like NASA's Kepler space telescope.

Transit surveys such as Kepler and TESS give a planet's radius, while radial-velocity measurements give its mass; Fortney's models convert that combination into estimates of composition, such as how large a gas envelope a sub-Neptune must have. His group also computes predicted spectra, which are compared against real observations from telescopes like Hubble and JWST.

His work spans hot Jupiters, sub-Neptunes, and super-Earths, with particular attention to the mass-radius relationships of the small planets that Kepler found in abundance. He has also worked on the thermal evolution and atmosphere models needed to understand young, directly imaged giant planets.