Recent maps of the surface of Venus suggest that early in the planet's history, it may have had a ocean, as well as a crust that underwent fragmentation and replenishment, just as Earth's does.
That's the word from a team of scientists led by Nils Müller, a researcher at the University of Münster and at the DLR Institute in Berlin. The group built its map from data gathered by the European Space Agency's Venus Express orbiter.
The map Müller & Co. put together provides some hints as to the chemical composition of the surface on Venus, particularly the highlands, where no lander has ever touched down to analyze the surface.
Rocks on two plateaus gave off infrared signatures similar to those given off by granite on Earth. Granite is reprocessed rock, forming under the intense heat and pressure that builds up when one crustal plate grinds beneath another.
The new map doesn't constitute proof, Müller cautions. "All we can really say at the moment is that the plateau rocks look different from elsewhere."
But, he adds, "If there is granite on Venus, there must have been an ocean and plate tectonics in the past."
The team published its results last December in the Journal of Geophysical Research. The European Space Agency -- in a bit of PR tectonics -- subducted the results, which resurfaced today.
The idea that Venus once had an ocean has been kicking around for years.
Generally, researchers have concluded that Venus is too close to the sun, and so is too hot, for water vapor in the atmosphere to condense and pool on the surface.
But other planetary scientists have long suggested that the planet could have hosted an ocean for perhaps its first 600 million years. Two years ago, a pair of US researchers noted that recent modeling studies of early Venus suggest that it could have hosted an ocean for more than a billion years.
Oceans on Venus?
The question of oceans on Earth's torrid twin (temperatures at its surface would melt lead) are intriguing for a couple of reasons.
The most obvious one: If Venus had an ocean for a billion years or longer and was tectonically active, the planet could have been quite hospitable to simple forms of life.
The other reason is a bit more subtle.
Dr. Müller and his colleagues point out that as humans hunt for Earth-like planets around other stars, they naturally hope to find such objects in a star's habitable zone -- a range of distances where temperatures would allow liquid water to accumulate on the surface and remain there.
If Venus is any indication, however, a position within a star's habitable zone -- in Venus's case, at the inner edge -- is no guarantee of long-term habitability.
Understanding Venus's early geophysical history would help researchers understand why the second rock from the sun drew the short straw on habitability -- thereby serving as a cautionary tale for scientists trying to interpret what they see around other stars.
In describing the recent modeling work on early oceans, the US duo -- David Grinspoon at the Denver Museum of Nature & Science and Mark Bullock at the Southwest Research Institute in Boulder, Colo. -- suggested lines of evidence that would bolster their case.
One of those lines: Finding granite-type rocks in the Venusian highlands.
Assuming Venus had an ocean, where did all that water go? Blown away by the solar wind, if earlier results from Venus Express are any indication.
Venus has no magnetic field to shield the planet from the effects of charged particles streaming from the sun. Collectively, these are known as the solar wind.
Last December, another Venus Express team reported that it had detected the solar wind blasting hydrogen gas away from the day side of the planet.
Earlier, the orbiter has detected hydrogen and oxygen streaming away from the planet on the night side -- a clear indication that water in Venus' atmosphere is being split into its hydrogen and oxygen atoms and carried into interplanetary space.
This was the first look at the daylight side of the process.