Schematic representation of cometary ion pickup. The ecliptic plane is shown and the magnetic field is assumed to be located in that plane. Cometary ions are created at rest with respect to the solar wind. These ions respond to the solar wind electric field by gyrating around the solar wind magnetic field. When fully picked up, the cometary ions form a ring distribution. The intersection of this ring with the plane that contains the magnetic field and the solar wind is shown. In response, the solar wind is deflected. The relatively small deflection shown in this schematic is consistent with the deflection in Fig. 2. DFMS has a very narrow field of view (shown by the green wedge) and detects low-energy ions from the comet. It does not detect the entire cometary ion distribution because pickup ions move in a direction and have an energy that is outside of the field of view and energy window of DFMS.