Scientists analysing data from the Cassini-Huygens mission have uncovered a significant structural surprise in Saturn’s protective magnetic bubble.
Researchers say this discovery confirms that giant planets operate under a different magnetospheric regime from the Earth’s.
The study in Nature Communications includes Dr Licia Ray and Dr Sarah Badman from Lancaster University with Dr Chris Arridge, formerly of Lancaster.
Cassini was sent to study the planet Saturn and its system, including its rings, natural satellites and local space environment, as part of a research mission by NASA, the European Space Agency (ESA) and the Italian space agency (ASI). It was in orbit between 2004 and 2017.
This latest research backs up a longstanding scientific theory that the rapid spin of massive planets like Saturn would replace the solar wind – the stream of charged particles from the Sun - as the dominant force sculpting their “magnetospheres”.
A magnetosphere is the region in the near-space environment where a planetary magnetic field acts as a shield against the solar wind. However, near the planetary poles, funnel-shaped openings called "magnetospheric cusps" allow charged particles from the Sun to leak directly into a planetary atmosphere.
Researchers analysed Cassini data collected between 2004 and 2010 to determine the precise location of Saturn’s magnetospheric cusp. The results showed a clear difference from similar measurements at Earth.
Saturn's immense rotational forces "drag" the cusp away from noon, skewing its average location significantly toward the afternoon sector, specifically between 13:00 and 15:00 local time while sometimes extending toward 20:00 local time. The dusk-oriented location of Saturn’s cusp confirms that a planet’s rotation rate can fundamentally change the structure of its near space environment
The shifted cusp location fundamentally alters models of magnetic reconnection, high-energy particle acceleration, and Saturn’s powerful auroral activity.
Dr Licia Ray of Lancaster University said: “This result allows us to move forward with new and improved theories on how planetary magnetospheres interact with the solar wind.”
Earth spins quite slowly compared to gas giants like Saturn. With one terrestrial day lasting 24 hours, the dominant factor driving the shape of the magnetosphere is the balance between the pressure from the Sun - the solar wind- and pressure from Earth’s magnetic field. This balance aligns the cusp towards local high noon.
At Saturn, one day lasts approximately 10.7 hours and its magnetosphere is full of ionised material from its moon Enceladus. These two effects mean that for Saturn, pressure from the magnetic field and a rapidly spinning disk of ionised material must balance the solar wind pressure.
Dr Ray said: “In particular, the afternoon cusp locations have implications for how we interpret Saturn’s bright aurora and where we expect magnetic reconnection, an explosive process that accelerates particles to very high energies of keV and more, to occur. It also highlights the rich science that can still be done with Cassini data more than eight years after the end of mission.”
Nature Communications
Data/statistical analysis
Not applicable
Dawn-dusk Asymmetrical Distribution of Saturn’s Cusp
1-Apr-2026