MINIMUM light-speed time lag to Mars is about 6 minutes one-way; it goes out to about 23 minutes or so at maximum (I'm doing this off the top of my head, using 1 AU is about 8 light-minutes, and Mars is at 1.7 AY, so distance from Earth ranges from 0.7 to 2.7 AU ....)
We do not posess FTL communication. We also do not have a presense on or near Mars. Therefore, if the probes respond to ANYTHING in less than light-speed lag time times 2 (round trip, you know ...), they're doing it on their own.
All we need to do (*all*, he says) is convince the Ipsos that we do not have FTL comm systems and we are not in the area, and they MUST accept probe sebntience.
Since they've taken Daniel apart, the should have been able to analyze his circuitry (indeed, Enoch found schematics ...); they should be able to verify on their own that there are no FTL comm devices on the probes. And they should be able to monitor the EM spectrum to see if there is any external control signals coming in; they could even isolate a probe in a Faraday cage or the equivalent so that communication outside is NOT possible, and then interact with the probe.
The probes are right - they will have top prove their own sentience. We can suggest ways the Ipsos can satisfy themselves, but its up to the probes to pull it off.
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This is Mission Control, in Houston.