QUESTION:
Can you listen to the Pathfinder when it is on the invisible side of Mars
(in the Martian night)?

ANSWER from Pieter Kallemeyn on July 28, 1997:
We cannot listen or talk to Pathfinder when it's on the other side of Mars
as seen from Earth (which is not exactly the same as the nightside).  The
radio signals to/from the lander require a direct line-of-sight to Earth.