Occultation
The intensity and phase changes observed in the 2300-mHz spacecraft telemetry signal as the spacecraft was occulted by the planet Mars were used to infer properties of the Martian atmosphere. The changes were the result of atmospheric refraction of the radio signal, and thus the data cover only the time near the planetary encounter when the signal was bent and slowed by the atmosphere (2 min on each side). Mars occulted the spacecraft signal with its sunlit side and the signal emerged on the night side.