Earth's magnetosphere is a relatively round and symmetrical bubble, almost perfectly aligned with the planet's axis of rotation. Saturn's, however, is far from being so well-structured. By analyzing data from the Cassini probe, researchers have discovered that this protective envelope is heavily deformed and off-center.
An international team has scrutinized six years of observations, aiming to precisely locate a region called the "cusp." This is where the magnetic field lines plunge toward the poles, channeling charged particles from the solar wind into the planet's atmosphere. Their observation is clear: this entry point for the field lines is not at all aligned with Saturn's axis of rotation. Seen from the Sun, it is systematically shifted to the right.
Diagram comparing the position of Saturn's magnetic "cusp" with Earth's.
Credit: SUSTech Two phenomena appear to work together to explain this configuration. On one hand, Saturn rotates at an exceptional speed, completing a full rotation on itself in just over ten hours. On the other hand, it moves through a dense plasma, an ionized gas, a good portion of which comes from the gigantic geysers of its icy moon Enceladus. The combination of this rapid rotation and this charged environment stretches and deforms the magnetic field lines, pulling them to the side.
This discovery is of major interest, particularly due to the attention given to Enceladus. This moon has a subsurface ocean of liquid water, whose plumes escape into space. And it is these plumes that would partly explain the shape of Saturn's magnetosphere.
Enceladus is one of the most promising places in the Solar System to look for signs of habitability, making it a priority destination for a future space mission. A link is now established between the shape of the planet's magnetosphere and the presence of a potentially habitable moon.
These mechanisms identified around Saturn could be transposable to other planets. Their work, published in
Nature Communications, suggests that the interaction between the solar wind and the magnetosphere may obey fundamental rules. This study provides a useful reference point for better understanding the environments of gas giants, including their moons, whether in our system or orbiting other stars.
To obtain these results, scientists used measurements from two instruments on the Cassini probe, with 67 separate passes through the cusp region between 2004 and 2010. This data allowed them to model Saturn's global magnetic field.