This graph illustrates the Cassini spacecraft's transition into Saturn's magnetosphere from an outer region called the magnetosheath. A magnetosphere is a magnetic envelope of charged particles that surrounds some planets, including Earth. In between it and a boundary called the bow shock -- where solar winds bend to avoid the magnetosphere -- is an area called the magnetosheath.
These data (bottom panel) were taken by Cassini's plasma spectrometer, which measures the energy and electric charge of particles such as protons and electrons. In this graph, the color green represents the highest intensity particles. The top panel shows the strength of the magnetic field as measured by the dual technique magnetometer instrument on Cassini. The field intensified as Cassini entered the magnetosphere.