Pioneer Venus was a NASA space mission launched in 1978 to study the planet Venus. It consisted of three spacecraft: Pioneer Venus Orbiter, which mapped the planet's surface and atmosphere, and two Pioneer Venus Multiprobe spacecraft, which studied the atmosphere and sent a lander to the surface. The mission provided valuable data about Venus' thick clouds, high temperatures, and atmospheric pressure. It helped scientists understand the planet's geology and climate, revealing that Venus has a rocky surface and volcanic features, contributing to our knowledge of planetary evolution in the solar system.