A Day in Astronomy: Pioneer Venus

Image (Credit): Artist’s version of the Pioneer Venus Orbiter above Venus. (NASA)

On this day in 1978, NASA launched Pioneer Venus from Cape Canaveral, Florida. The mission had two components:

  • the Pioneer Venus Orbiter that remained in orbit around the planet until 1992 when it entered the Venusian atmosphere and burned up, and
  • the Pioneer Venus Multiprobe (known as Pioneer 13) that carried four probes later dropped into the Venusian atmosphere.

NASA described the descent of the four probes:

When the probes separated from the Multiprobe bus, they went “off the air” because they did not have sufficient on-board power or solar cells to replenish their batteries. Preprogrammed instructions were wired into them and their timers had been set before they separated from the bus. The on-board countdown timers were scheduled to bring each probe into operation again three hours before the probes began their descent through the Venusian atmosphere. On 9 December 1978, just 22 minutes before entry, the Large Probe began to transmit radio signals to Earth. Only 17 minutes before hurtling into the Venusian atmosphere at almost 42,000 km/hr (26,100 mph), all the Small Probes started transmitting.

All four probes were designed for a descent time of approximately 55 minutes before impacting the surface. None were designed to withstand the impact. However one Small Probe (the Day Probe) did survive and sent data from the surface for 67 minutes. Engineering data radioed back from the Day Probe showed that its internal temperature climbed steadily to a high of 126 degrees C (260 degrees F). Then its batteries were depleted, and its radio became silent.

A 2020 Nature Astronomy article noted that one of the probes may have detected signs of life in the Venusian atmosphere. The paper, Phosphine Gas in the Cloud Decks of Venus, has been controversial and was later modified to clarify some of the findings. However, a separate study in the Geophysical Research Letter, Venus’ Mass Spectra Show Signs of Disequilibria in the Middle Clouds, confirmed some of these finding and adding to the argument with the discovery of other chemicals that could also be linked to biological processes. The debate will continue as we learn more.