One of my good friends is a scientist, working for some kind of radio telescope organization - I forget the name, but maybe it started with an S? Anyway, she told me that yesterday her team picked up an intense narrowband radio signal, out of the blue, that beamed for around a minute and then disappeared. It was of unknown origin, and their only clue was that it was preceded by a weak telemetry signal from what she described as "a very old spacecraft, one from back in the seventies." It piqued my interest, so I asked her what the mysterious signal said.
This is what she sent me. I'm sure you agree that parts of it appear to have been classified. I'm not sure why that would be...
She told me the team had been working to decode it and they could use the help of a puzzler like me, but I had to promise to keep it a secret. Unfortunately, I've racked my brains and I can't figure this one out, so I've decided it's probably fine to share this with you so you can have a crack at it. In the meantime I should - hang on, there's two strangely dressed people at my door -
[FURTHER INFORMATION REDACTED, CONTENTS CLASSIFIED BY PDP. USER "SCIBORG" HAS BEEN DETAINED FOR INVESTIGATION.]
PDP REPORT: Prisoner #24254 "Sciborg" managed to briefly escape federal prison long enough to shout at some patrons in a roadside diner before being caught and re-detained by our agents.
I've just figured out what she was talking about with the spacecraft! They must have gotten the message and replied - they understood the transition, they're using - oh God they're coming back for me -
PDP REPORT: Prisoner #24254 "Sciborg" has escaped again and was ranting incoherently before being captured.
The plaque, it's all the plaque! They're showing us they understand. The transition state of the molec -
Big Last Hint:
PDP REPORT: Prisoner #24254 "Sciborg" released from federal prison, almost incapable of speech but managed to eke out some words before collapsing.
Isoto - iso... the plaque molec... the particles, prot... that's the key...