The bow shock is a boundary that forms as a result of an obstacle downstream of a supersonic flow. The boundary is characterised by a sharp change in speed, density and temperature of the particle flow. The magnetosphere (region controlled by the magnetic field) of Saturn forms such an obstacle to the flow of particles that leave the Sun as the solar wind (Saturn's bow shock can be pictured as the blue region in the image below).

 

During Saturn orbit insertion, the Cassini magnetometer and plasma spectrometer obtained in-situ measurements of the magnetic field and plasma conditions associated with Saturn’s environment. A total of 51 bow shock crossings near the dawn sector were found in the 2004 orbit with the aid of a machine learning algorithm. Analysis of the magnetic field data indicated that Cassini repeatedly crossed a quasi-perpendicular bow shock boundary on both inbound and outbound passes. Using statistical techniques such as kurtosis, it was found that most of the shock angle distributions for bow shock crossings have kurtosis less than 3, meaning a heavy-tailed distribution. This suggested that the bow shock boundary may be moving rapidly or strongly accelerating in many cases which resulted in more values of shock angle in the tail of the distribution.