The European Space Agency has an interesting news release about some new mapping data from its Venus Express spacecraft:
Venus Express has charted the first map of Venus’ southern hemisphere at infrared wavelengths. The new map hints that our neighbouring world may once have been more Earth-like, with a plate tectonics system and an ocean of water.
The fact that the instruments operate at infrared wavelengths makes it possible for them to “see” thorough the cloud layer that covers Venus. The map is built up from over 1,000 images taken from May 2006 to December 2007.
Earlier Russian spacecraft, which landed on the planet’s surface, touched down in relatively low-lying areas, and found rock basically similar to basalt, an igneous rock. The infrared mapping includes some higher plateaus, and is capable of giving some information on the chemical composition of the surface rock, based on its emissivity in the infrared portion of the spectrum. The rocks on the plateaus appear “lighter” than those in the lower-lying areas. On Earth, this kind of difference usually means that one is looking at granite, rather than basalt. And the presence of granite has implications for the history of the area:
Granite is formed when ancient rocks, made of basalt, are driven down into the planet by shifting continents, a process known as plate tectonics. The water combines with the basalt to form granite and the mixture is reborn through volcanic eruptions.
If the inference that the lighter rock is granite is correct, it suggests that Venus may at one time have had plate tectonics similar to those on Earth. One interpretation is that the higher “plateaus” were once continents, surrounded by seas of water:
The new data are consistent with suspicions that the highland plateaus of Venus are ancient continents, once surrounded by ocean and produced by past volcanic activity.
“This is not proof, but it is consistent. All we can really say at the moment is that the plateau rocks look different from elsewhere,” says Nils Müller at the Joint Planetary Interior Physics Research Group of the University Münster and DLR Berlin, who headed the mapping efforts.
The mapping instruments did not detect any really large temperature differences, as might be seen after recent volcanic activity, but they did find “darker” areas, which might be the remnants of past lava flows.
Venus, as a planet similar in size to the Earth, is still something of an enigma, but the new data will perhaps provide some more clues to why it evolved so differently from the Earth.