Pioneering Venus Date: 5 Feb 1979 The forecast for Venus is cloudy, cloudy, cloudy. Although similar to the Earth in size and mass, Venus' slightly closer orbit to the Sun create for it a much thicker atmosphere and a much hotter surface. The thick atmosphere was photographed above in ultraviolet light in 1979 by the Pioneer Venus Orbiter. Venus's extremely uncomfortable climate was likely caused by a runaway greenhouse effect.
Pioneer Venus used an orbiter and several small probes to study the planet from above and within the clouds.
