New results from NASA’s Cassini mission to Saturn are causing scientists to rethink their understanding of magnetic fields after observations revealed that the one belonging to the planet has no discernable tilt.
The surprising data is one of the early insights from the final phase of Cassini's mission to Saturn and its rings, known as the Grand Finale.
Up to now scientists held the belief that for planets to generate magnetic fields, there must be a tilt between its rotation axis and its magnetic field axis.
This was considered necessary to sustain currents flowing through the liquid metal deep inside the planets – which in Saturn's case is thought to be liquid metallic hydrogen.
Without the tilt, it was understood that the currents would eventually subside and the field would disappear. This new finding from Cassini's magnetometer instrument is directly at odds with this theoretical analysis, however.
The data indicated that Saturn's magnetic field is surprisingly well-aligned with the planet's rotation axis.
Mission scientists previously assessed that 0.06 degrees would be the lower limit of tilt that could generate the observed magnetic field. The tilt observed is apparently much smaller than this.
"The tilt seems to be much smaller than we had previously estimated and quite challenging to explain," said Michele Dougherty, Cassini magnetometer investigation lead at Imperial College, London.
It also leaves the mystery of how long a day is on Saturn unresolved.
"We have not been able to resolve the length of day at Saturn so far, but we're still working on it,” Dougherty said.
Establishing the length of a day on Saturn has proved a consistent challenge due to the swirling gases visible on the surface which make it impossible to track a point on the surface as the planet rotates.
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Dougherty and her team hope they will be able to rectify the conundrum around Saturn’s lack of tilt with further data during the final plunge into the gas giant.
It’s a strong possibility that some aspect of the planet's deep atmosphere might be masking the true internal magnetic field, according to researchers at Imperial College, London.
Cassini is now in the 15th week of 22 weekly orbits that see it pass through the narrow gap between Saturn and its rings.
The spacecraft began its finale on April 26 and will continue its dives through varying parts of the ring gap before plunging into Saturn's atmosphere on September 15.