Those who follow science news have been excited these past few years by the repeated evidence from NASA (via the Mars Polar Lander and the Spirit and Opportunity rovers) that Mars was once covered with briny seas, just like Earth. Enticing evidence from vapor plumes encounted by Cassini on the Saturnian moon Enceladus suggested the possibility of oceans under the ice (although the sodium signature of those plumes would later cast doubt on that.)
Now comes stunning hints from the ESA's Venus Express that the planet Venus may once have been a world of continents and oceans!
More below the fold...
Long before Venus became a hot, dry and barren planet with a choking mass of carbon dioxide for an atmosphere, it might have once been home to shifting continents and an ocean of water, according to the latest data from a European space probe.
Using infrared images of the planet's southern hemisphere taken in 2006 and 2007 from the Venus Express probe, German astronomers say they have produced a map that reveals the planet's highland plateaus were likely once ancient continents surrounded by water.
Of course today, Venus has no plate tectonics: it is thought that volcanism destroyed the surface of Venus about 750 million years ago, and the increasing heat and lack of water, combined with this, shut down subduction, and thus (presumably) all carbon sequestration.
On Earth, the presence of life, vast oceans, and plate tectonics, allows carbon dioxide to be absorbed back out of the atmosphere. This prevents the runaway greenhouse effect visible on Venus.
But to think that Venus was once a watery world (like Earth is and Mars was) suggests that it may be a natural state of rocky planets to be covered with water at some point in their existence - which further suggests life may be very, very common in the habitable zones of planet carrying stars.
This is what Venus would be like today.
A Russian probe actually landed on Venus and took pictures. The Venera 13 probe, part of a 23 year Russian effort to learn about Venus, took these shots (click the thumbnail images below) in 1982. A predecessor, Venera 9, was the first to send back such images in 1975.