
So, when the aliens brought you back,
they just left the PROBE in?
The Big Bang Theory Season 9, Episode 23

Voyager the space PROBE,
or Voyager the Star Trek TV show?
The Big Bang Theory Season 8, Episode 6

Is this about the PROBE
he's working on without you?
The Big Bang Theory Season 8, Episode 21

The plaque they sent on the Pioneer PROBE
had a drawing of a naked man and woman.
The Big Bang Theory Season 8, Episode 21

And, of course, it's Gravity Probe B.
The Big Bang Theory Season 1, Episode 13