Voyager 2’s Magnetic Encounter with Neptune: The Excitement and Anticipation in the JPL Prediction Pool

On August 23rd, we eagerly awaited the boundary of Neptune’s influence in the solar wind. We created a prediction pool at the Jet Propulsion Laboratory to guess when Voyager 2 would encounter the “bow shock” of the planet’s magnetosphere. A list was written on a chalkboard in one of our rooms, with predictions made in Pacific Daylight Time-Earth Received Time (PDT-ERT), which was when data arrived back at JPL in California.

The prediction list only had five entries, starting from Day of Year (DOY) 235. The one-way light time during the flyby was 4 hours and 6 minutes. To convert spacecraft event time (SCET) from PDT-ERT to Greenwich Mean Time (GMT), we added 7 hours and then subtracted 4 hours and 6 minutes to adjust for the spacecraft’s time.

My prediction was later than others, as I anticipated a smaller magnetic field that would be seen closer to the planet. I predicted 12 noon on DOY 236, which translates to August 24th at 1454 GMT-SCET. However, it is remarkable that this event was documented and that a photo of the prediction list still exists today, capturing our excitement and anticipation leading up to Voyager’s encounter with Neptune’s magnetosphere.