Saturn’s hexagon in an image taken by the Imaging Science Subsystem (ISS) on board the Cassini spacecraft on 26 February 2013. Credit: Planetary Science Group UPV/EHU-Cassini NASA/ESA

A hexagon-­shaped atmospheric phenomenon first spotted on Saturn by Voyager 1 and Voyager 2 has intrigued scientists since the 1980s. More recently, NASA’s Cassini mission has periodically observed the hexagon and its embedded strong eastward jet that rotates at 120 meters per second. Scientists believe that the persistence of the hexagon could put to rest the oft-­debated question of the length of Saturn’s rotational period.

Sánchez-­Lavega et al. have presented an estimate (in Earth hours) of the length of Saturn’s day based on data from Cassini and ground-­based images. They tracked the movement of Saturn’s hexagon for 5.5 years and found that despite large radiative forcing in Saturn’s atmosphere, the rotation of the hexagon remained constant. These findings suggest that the hexagon is deeply rooted within Saturn’s atmosphere and that its rotational period could reveal the rotational period of Saturn’s internal solid body, which the authors estimate as 10 hours, 39 minutes, and 23.01 ± 0.01 seconds. (Geophysical Research Letters, doi:10.1002/2013GL059078, 2014)

—JoAnna Wendel

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