1978 - The U.S. launches the Pioneer Venus, which is composed of two craft - Venus Orbiter and Venus Multiprobe. The Multiprobe sends four probes to Venus. It then falls to the surface. The probes parachute to the surface but quickly fail. The Orbiter, however, uses radar to study the surface. It also finds sulfur in the atmosphere, which might come from volcanoes. The atmospheric data on cloud layers confirms that the greenhouse effect is responsible for Venus's temperature.
1984 - The Soviets launch Vega 1 and 2 to gather information on Halley's comet. On the way, they drop off probes into Venus's atmosphere and collect data on atmospheric gases.
