Predicted temperatures for Pioneer 10 at 25 AU
The thermal model developed by Slava Turyshev and colleagues predicted a range of temperatures for the surface of the Pioneer 10 equipment and instrument compartments, from a low of -2.3 degrees Celsius (28 degrees Fahrenheit) to a high of 8.6 degrees Celsius (47 degrees Fahrenheit). The compartment is insulated from space by a blanket of multi-layer insulation (MLI), whose surface temperatures are much colder, from -161.8 to -119.1 degrees Celsius (-259.2 to -182.4 degrees Fahrenheit). These temperatures only hold for when Pioneer 10 was 25 Astronomical Units from the Sun, in July of 1981.
NASA / JPL / Slava Turyshev