Phase light curves for extrasolar Jupiters and Saturns

We predict how a remote observer would see the brightness variations of giant planets similar to those in our Solar System as they orbit their central stars. We model the geometry of Jupiter, Saturn and Saturn’s rings for varying orbital and viewing parameters. Scattering properties for the planets and rings at wavelenghts 0.6-0.7 microns are assumed to follow these observed by Pioneer and Voyager spacecraft, namely, planets are forward scattering and rings are backward scattering. Images of the planet with or without rings are simulated and used to calculate the disk-averaged luminosity varying along the orbit, that is, a light curve is generated. We find that the different scattering properties of Jupiter and Saturn (without rings) make a substantial difference in the shape of their light curves. Saturn-size rings increase the apparent luminosity of the planet by a factor of 2-3 for a wide range of geometries, an effect that could be confused with a larger planet size. Rings produce asymmetric light curves NASA/Goddard Institute for Space Studies, 2880 Broadway, New York, NY, 10025, USA Planetary Science Institute, Australian National University, ACT, 0200, Australia Victoria University of Wellington, New Zealand