Measuring Day Length of the Gas Giants

Environmental & Science Education
STEM
Solar System
Astronomy
Edward Hessler

I'd never thought about the problems of measuring the day length of the "gas giants," four planets found in the outer solar system. They are Jupiter, Saturn, Uranus, and Neptune.

These planets can be thought of as wearing veils of gases that are in turbulent motion. These shield fixed interiors rendering the use of surface objects on which to base measurements. To see through these veils, astronomers have made use of radio waves created by the planetary magnetic fields.

There is a short article in Science (October 4 2018) by Paul Voosen that includes an animated video on how such measurements are made and interpreted. The focus is Saturn which is not as straightforward a calculation as the others. Studies have revealed a deeper challenge in making the  measurements and then in interpreting them. The studies also raise the question of why Saturn has a magnetic field in the first place.