The planet Venus may not have always been the hot and barren ball of rock that we see today. A new analysis of its surface indicates that it might once have had oceans of liquid water–which could have allowed for a brief flourishing of microbial life.
Researchers examined nighttime infrared emissions coming from Venus’ surface, and found that the planet’s highland regions emit less infrared radiation than its lowland regions. One interpretation of this lower infrared emission from the highlands, say the authors, is that they are composed largely of ‘felsic’ rocks, particularly granite. Granite, which on Earth is found in continental crust, requires water for its formation…. “This is the first direct evidence that early in the history of the Solar System, Venus was a habitable planet with plenty of water,” says [astrobiologist] Dirk Schulze-Makuch…. “The question is how long Venus remained habitable. But this gives new impetus for the search for microbial life in Venus’s lower atmosphere” [Nature News].
Even if Venus did have vast watery expanses shortly after the planet formed around 4.5 billion years ago, 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. Nowadays, the planet is a paragon of the uninhabitable [Nature News]. It’s atmosphere is 96 percent carbon dioxide, and its surface temperature routinely reaches 860 degrees Fahrenheit. The researchers report their marine hypothesis in the Journal of Geophysical Research [subscription required].
The lack of water in the planet’s atmosphere poses a separate puzzle. If all the water from those oceans boiled off, where did it go? In an attempt to answer this question, a different research team examined the composition of the atmosphere with instruments aboard the European Space Agency’s Venus Express spacecraft. They found evidence for the loss of hydrogen from the atmosphere on Venus’ day side, or the side facing the sun. The finding suggests the solar wind, a stream of charged particles from the sun, could be responsible for stripping away the hydrogen atoms. The hydrogen may have been part of water molecules (H2O) [LiveScience], researchers will report in the journal Geophysical Research Letters. While the solar wind buffets Earth too, our planet’s magnetic field protects us from its force. Venus has no such protective sheath.