9 December

1978: On 9 December 1978, NASA's Pioneer Venus Multiprobe (PVM) entered the atmosphere of Venus.

PVM consisted of a 'bus', a vehicle which carried one large and three small atmospheric probes. The large probe was released on 16 November 1978 and the three small probes on 20 November. All four probes entered the Venus atmosphere on 9 December, followed by the bus.

The Pioneer Venus large probe was equipped with seven science experiments, contained within a sealed spherical pressure vessel.

Each small probe carried a 'nephelometer' (an instrument for measuring or registering the amount of cloudiness) and temperature, pressure and acceleration sensors.

The radio signals from all four probes were also used to characterise the winds, turbulence and propogation in the atmosphere. The probes were each targeted at different parts of the planet.