This is pretty neat. After over twenty years, it's still possible to communicate with Pioneer 10, even though it's almost seven and a half billion miles away (twice the distance to Pluto, the most distant planet) and far outside our solar system. It took over twenty-two hours for the signal to be received and acknowledged. From there, the sun is just another bright star, and there is no heat for the spacecraft except what it can still generate from its depleting plutonium power generator.

This would not have been possible if it had had any other than a nuclear power source.

The numbers involved here are staggering. It's so far away, and the signal so diffuse, that by the time it reaches the earth, it has a power of only ten to the minus 20th or so watts. That's 0.00000000000000000001 (that's nineteen zeros after the decimal point). But we can still pick up the signal, using the huge dishes in places like Goldstone in California.

And the data rate is probably excruciatingly low.

Given the ability to get just a few bits through, I wonder what the conversation was...

Ground: Hello, Pioneer. Are you out there?

Pioneer: Yes.

Ground: How are you doing?

Pioneer: How do you think I'm doing? I'M FREEZING IN THE DARK! What did you think you were doing, sending me all the way out here?! And why don't you ever write?