We all know time is relative, just like we know that the plates are moving around underneath us, but both time and that the earth is not moving still 'ground' us on a daily basis.
On Saturn, that can all be a little confusing. Unlike Earth, which has a visible rocky surface and rotates once every 24 hours, Saturn is composed mostly of clouds and liquid gas layers, each rotating about the planet at its own rate of speed. This variation in rotation made it difficult for scientists to pin down time for the planet. And Saturn's magnetosphere is the third largest structure in the solar system, eclipsed only by the magnetic fields of the sun and Jupiter, meaning the north and south poles have their own 'days' that vary over periods of weeks or even years. Good luck getting a traditional watch to work.
Decades ago, a strong and naturally occurring radio signal, called Saturn kilometric radiation (SKR), was believed to give an accurate measurement of a Saturn day but spacecraft data proved otherwise and data from NASA's Cassini spacecraft, which entered orbit around Saturn in 2004, has given us one of the first direct observations of seasonal changes in Saturn's magnetosphere. In addition, the finding carries over to all planets having a magnetosphere, including Earth.
Tim Kennelly, a University of Iowa junior majoring in physics and astronomy, is lead author of the paper in the Journal of Geophysical Research.
Saturn's magnetospheric processes are linked together. The activity generating the SKR emission relatively near the planet to the periodic signatures in Saturn's magnetosphere stretching millions of miles downstream in the planet's magnetotail shows that. But how they were linked has been unclear.
Kennelly analyzed phenomena recorded between July 2004 and December 2011 by Cassini's Radio and Plasma Wave Science (RPWS) instrument to make some determinations about how the events are linked. First, he looked at inward-moving "flux tubes" composed of Saturn's plasma - the hot, electrically charged gas. Focusing on the tubes when they initially formed and before they had a chance to dissipate under the influence of the magnetosphere, he found that the occurrence of the tubes correlates with activity in the northern and southern hemisphere depending upon the season.
Kennelly found that during winter in the northern hemisphere, the occurrence of flux tubes correlates with SKR period originating in the northern hemisphere. A similar flux tube and SKR correlation was noted for the southern hemisphere during southern winter. The events are strongly ordered, he says, and follow Saturn's seasonal changes.
This finding may alter how scientists look at the Earth's magnetosphere and the Van Allen radiation belts that affect a variety of activities at Earth ranging from space flight safety to satellite and cell phone communications.