Global Climate Change on Venus; March 1999; Scientific American Magazine; by Bullock, Grinspoon; 8 Page(s)

Emerging together from the presolar cauldron, Earth and Venus were endowed with nearly the same size and composition. Yet they have developed into radically different worlds. The surface temperature of Earth's sister planet is about 460 degrees Celsius-hot enough for rocks to glow visibly to any unfortunate carbonbased visitors. A deadly efficient greenhouse effect prevails, sustained by an atmosphere whose major constituent, carbon dioxide, is a powerful insulator. Liquid water is nonexistent. The air pressure at the surface is almost 100 times that on Earth; in many ways it is more an ocean than an atmosphere. A melange of gaseous sulfur compounds, along with what little water vapor there is, provides chemical fodder for the globally encircling clouds of sulfuric acid.

This depiction of hell has been brought to us by an armada of 22 robotic spacecraft that have photographed, scanned, analyzed and landed on Venus over the past 37 years. Throughout most of that time, however, Venus's obscuring clouds hindered a full reconnaissance of its surface. Scientists' view of the planet remained static because they knew little of any dynamic processes, such as volcanism or tectonism, that might have occurred there. The Magellan spacecraft changed that perspective. From 1990 to 1994 it mapped the entire surface of the planet at high resolution by peering through the clouds with radar [see "The Surface of Venus," by R. Stephen Saunders; Scientific American, December 1990]. It revealed a planet that has experienced massive volcanic eruptions in the past and is almost surely active today. Coupled with this probing of Venusian geologic history, detailed computer simulations have attempted to reconstruct the past billion years of the planet's climate history. The intense volcanism, researchers are realizing, has driven large-scale climate change. Like Earth but unlike any other planet astronomers know, Venus has a complex, evolving climate.