Figure 3.

He⁺ energy spectra upstream of Pluto (blue) and within Pluto's wake (green). The spectra are shown in the spacecraft frame. It can be seen that the Pluto interaction mostly affects the overall amplitude but only barely the spectral shape. Measurements are taken with a cone angle of 34° to the Sun. The vertical dashed line shows the expected interstellar pickup ion cutoff energy based on the upstream solar wind measurements, the observation angle, and assuming the ions are He⁺. Error bars show the Poisson error of the event data counts. DOY = day of year.