No. of Recommendations: 2
While not a hard edge, or a "wall" as it has sometimes been called, here both spacecraft measured temperatures of 30,000-50,000 kelvin (54,000-90,000 degrees Fahrenheit), which is why it is sometimes also referred to as a "wall of fire".
This is somewhat misleading. The spacecraft are in hard vacuum, which means not very many atoms are out there. So yeah, maybe the temperature is high, but the heat transfered is extremely low. Although not SI, let's use torr as the measure of pressure. 760 torr is one atmosphere. Ultra-High-Vacuum (UHV) is roughly comparable to the vacuum of deep space. It can be achieved in the laboratory but requires stainless steel chambers, copper gaskets, baking to get rid of adsorbed water on the walls of the chamber, etc, and the result is about 10^-10 torr. So 13 orders of magnitude below one atmosphere. Which means that instead of 10^23 atoms in 5 gallons of vacuum you have 10^10 atoms in that volume. So what does temperature mean when the atoms doing the "temperaturing" are 13 orders of magnitude below what we are used to when we deal with convective heat transfer?
What is more amusing is that at that low a pressure the mean free path between collisions becomes really big (planet-sized). So I dunno what temperature even means with that small an atomic density. The atoms are mostly hydrogen and helium and there are still some alpha particles (helium nuclei) that were emitted from the sun, and then a large number of neutrinos (but then, you ain't getting temperature from those). So without a better explanation of what they mean by temperature I dunno, that number doesn't have much meaning?
But more importantly, the Voyager missions are amazing. To still be going after all these years, dependent on that chunk of Pu^239 as their electricity source (too far away for solar panels). The best of what we were capable of doing back then, when science was the reason to do stuff. God speed!
Rgds,
HH/Sean
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Yes, it is somewhat deceptive. People think of a really really hot furnace (for example), in which the probes would sublimate in an instant at 50K kelvins.
Basically, it refers to a plasma temperature at the boundary. However, the plasma is so thin (as you said with your mean-free-path), that it isn't really a barrier, or even damaging. It's -in essence- the energy of the plasma constituents, but they are very spread out.
