Saturn surprises as Cassini continues its grand finale

As NASA’s Cassini spacecraft makes its unprecedented series of weekly dives between Saturn and its rings, scientists are finding that the planet’s magnetic field has no discernable tilt. This surprising observation, which means the true length of Saturn’s day is still unknown, is just one of several early insights from the final phase of Cassini’s mission, known as the Grand Finale. Other recent science highlights include promising hints about the structure and composition of the icy rings, along with high-resolution images of the rings and Saturn’s atmosphere.

Cassini is now in the 15th of 22 weekly orbits that pass through the narrow gap between Saturn and its rings. The spacecraft began its finale on 26th April and will continue its dives until 15th September when it will make a mission-ending plunge into Saturn’s atmosphere. Based on data collected by Cassini’s magnetometer instrument, Saturn’s magnetic field appears to be surprisingly well-aligned with the planet’s rotation axis. The tilt is much smaller than 0.06 degrees which is the lower limit the spacecraft’s magnetometer data placed on the value prior to the start of the Grand Finale.

This observation is at odds with scientists’ theoretical understanding of how magnetic fields are generated. Planetary magnetic fields are understood to require some degree of tilt to sustain currents flowing through the liquid metal deep inside the planets. With no tilt, the currents would eventually subside and the field would disappear.

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