3.04.2026

NASA/JPL/Space Science Institute

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.”

Quelle: Lancaster University

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Saturn’s magnetic bubble is lopsided compared to Earth’s

Saturn's magnetic shield is asymmetrical compared to Earth’s, suggests a new study involving UCL researchers, and this is likely a result of its fast rotation coupled with the heavy material it pulls around it.

Planetary magnetic fields (magnetospheres) shield planets from the highly charged particles of the solar wind. Saturn’s field is vast, more than 10 times wider than the planet itself.

The new study, published in Nature Communications, looked at six years of data from the Cassini space mission to determine the precise location of Saturn’s cusp - where magnetic field lines start to curve back into the planet’s poles and funnel charged particles down into the atmosphere.

The team found that the cusp was dragged to the right as viewed from the Sun, and was located most often between 13:00 and 15:00 (as it might appear on a clockface), compared to 12:00 as it would be on Earth.

The researchers said this was likely because of Saturn’s extremely fast rotation (a Saturn day is 10.7 hours) and the heavy “soup” of plasma (ionised gas) it pulls around it, a product of gases emitted by Saturn’s moons, especially Enceladus. Together, these are thought to drag the magnetic field lines to the right. But more simulations are needed to confirm this interpretation.

The environment around Saturn is of particular interest given that its moon Enceladus, which has icy plumes emanating from a subsurface ocean, may even host life and is the planned destination of a major European Space Agency mission proposed for launch in the 2040s.

Co-author Professor Andrew Coates (Mullard Space Science Laboratory at UCL) said: “The cusp is the place where the solar wind can slip directly into the magnetosphere. Knowing the location of Saturn’s cusp can help us better understand and map the whole magnetic bubble.

“A better understanding of Saturn’s environment is especially urgent now as plans for our return to Saturn and its moon Enceladus start to be developed. These results feed into the excitement that we are going back there. This time we will look for evidence of habitability and for potential signs of life.

“This study also provides critical evidence for a long-held theory – that the rapid spin of massive planets like Saturn with active moons replaces the solar wind as the dominant force shaping magnetospheres. It shows that Saturn’s magnetosphere, as well as the magnetospheres of other rapidly spinning gas giants, likely differ fundamentally from Earth’s.”

“Enceladus itself is a key driver of this environment, releasing huge amounts of water vapour that gets ionised, loading the magnetosphere with heavy plasma that is then pulled around as the planet spins.”

The international study team was led by researchers at the Chinese Academy of Sciences, the Southern University of Science and Technology, and the University of Hong Kong.

Corresponding author Professor Zhonghua Yao (The University of Hong Kong) said: “The differences between Saturn’s magnetic structure and that of Earth point to a unified fundamental process governing solar wind interaction across different planets. Comprehensive terrestrial observations reveal the working mechanisms of Earth, while comparative studies between planets inform us of the fundamental laws that can be applied to understand other systems, such as exoplanets.”

Lead author Dr Yan Xu (Southern University of Science and Technology in China) said: “By combining Cassini observations with simulations, we found that Saturn's rapid rotation and the plasma from its moon Enceladus together shape the asymmetric global distribution of the cusps. We hope this gives some useful reference for future exploration of Jupiter's and Saturn's space environments.”

The researchers looked at data from two of Cassini’s instruments (the Cassini Magnetometer, or MAG, and Cassini Plasma Spectrometer, CAPS) to detect moments where the spacecraft flew through Saturn’s cusp. They found 67 such events in total across the years 2004 to 2010, indicated through such clues as the energy levels of electrons the sensors detected.

Drawing on this data, the researchers carried out simulations of the magnetic field, finding that interactions between the magnetic field and solar wind at the edge of the magnetosphere closely resembled that of Jupiter’s.

A key source of data for the study came from the CAPS’s electron sensor, which was developed by a team led by Professor Coates at the Mullard Space Science Laboratory at UCL.

The researchers received funding from the UK’s Science & Technology Facilities Council and the National Natural Science Foundation of China, among other institutions.

Quelle: University College London