An empirical model of Saturn's bow shock: Cassini observations of shock location and shape

We present a new empirical model of Saturn's bow shock that utilizes observations from the Cassini spacecraft. Shock crossings are identified in magnetic field and plasma observations made by Cassini between June 2004 and August 2005. The Cassini crossings are then combined with the crossings made during the Saturn flybys of Pioneer 11, Voyager 1, and Voyager 2. Solar wind dynamic pressures for the Cassini crossings are estimated using upstream electron densities determined from Langmuir wave observations made by the Radio and Plasma Wave System. The crossing positions are rotated into aberrated coordinates to correct for the effect of the planet's orbital motion. In the case of Saturn this rotation is by ∼1°. To correct for solar wind dynamic pressure variations, the crossing positions are normalized to the average pressure 〈P SW 〉 = 0.048 nPa. The model is then obtained by fitting a conic section to the crossings using a nonlinear least squares technique. To validate the assumptions made in constructing the model, we treat the parameters previously assumed to be constants as variables and fit their values using an optimization routine; this leads to a conic section that is within the positional uncertainty of the model. The spacecraft trajectories are considered, and we conclude that they do not significantly bias the model. The new model is compared to the existing models, and the similarities and differences are discussed. We suggest that the new model gives the most accurate empirical representation of the shape and location of Saturn's bow shock.