A new look at data gathered from the Galileo spacecraft in 1990 reveals that Venus at one time may have been habitable, with evidence of past continents and oceans. In a flyby of Venus on the spacecraft’s journey to Jupiter, a near-infrared mapping instrument detected signatures which the researchers have interpreted as granite. An international team led by planetary scientist George Hashimoto, at Okayama University, Japan, found that Venus’s highland regions emitted less infrared radiation than its lowlands. One interpretation of this dichotomy, says the team’s new paper, is that the highlands are composed largely of ‘felsic’ rocks, particularly granite. Granite, which on Earth is found in continental crust, requires water for its formation.
The Galileo spacecraft was the first use of infrared to look at Venus. Scientists had believed that only radar could see through the dense clouds of sulfuric acid in Venus’s atmosphere to the surface. “Detecting the surface in the infrared is a breakthrough,” co-author Kevin Baines from JPL was quoted in an article in Nature.
The article also quoted another JPL scientist, David Crisp, who was not involved in this study as saying these new conclusions aren’t supported either by the available data or the team’s own models.
“We understand our paper doesn’t resolve everything,” responds co-author Seiji Sugita, a planetary scientist at the University of Tokyo. Sugita says the next step is to apply their models to data from the European Space Agency’s Venus Express spacecraft, which is already orbiting Venus, and the Japanese Space Agency’s Venus Climate Orbiter, scheduled for launch in 2010.
The possible presence of granite suggests that tectonic plate movement and continent formation may have occurred on Venus, as well as recycling of water and carbon between the planet’s mantle and atmosphere.
Venus is now hellishly hot and dry, with an atmosphere of 96% carbon dioxide and a surface temperature of around 460 degrees C, but some scientists think our neighboring planet may have once have been more like Earth.
Another scientist quoted in the Nature article, geophysicist Norm Sleep of Stanford University in California said Venus might have once been almost entirely underwater. “Although without further geochemical data, he adds, we don’t know whether this early ocean’s temperature was 30 degrees C or 150 degrees C,” he said.
But any ocean on Venus would have lasted only a few hundred million years. As the Sun became hotter and brighter, the planet experienced a runaway greenhouse effect. “Any life on Venus that hadn’t figured out how to colonize the cloud tops a billion years after the planet’s formation would have been in big trouble,” says Sleep.