A team of planetary researchers from the Lunar and Planetary Institute (LPI) and elsewhere has found that a volcanic flow on Venus’ Ovda Regio highlands plateau is made of basaltic lava and isn’t silica-rich. This discovery weakens the notion that Venus might once have been Earth-like with an ocean of liquid water.

Venus is one the most hostile places in the Solar System. Its atmosphere is composed almost entirely of carbon dioxide (96.5%), with very little water vapor. It also has significant amounts of corrosive sulfur-bearing gases and rapidly moving clouds of sulfuric acid droplets.

Despite only 10% of the solar flux reaching the planet’s surface, enough energy is trapped by gases and particles present in the lower atmosphere, to raise the temperature at the surface dramatically. This extreme ‘greenhouse effect’ heats the surface to temperatures as high as 864 degrees Fahrenheit (462 degrees Celsius).

Walking on the Venusian surface would be difficult, like walking under water at 900 m (2,950 feet) depth — the atmospheric pressure is 90 times higher than on Earth at sea level.

Previous studies suggested that early Venus was once warm and wet based on the chemistry of its atmosphere and the presence of highlands.

These highlands were thought to be formed of granitic rock, like Earth’s continents, which required oceans of water to form.

In the new study, LPI researcher Dr. Allan Treiman and colleagues found that Ovda Fluctus, a lava flow complex on the equatorial highlands of Ovda Regio, is composed of basaltic lava, calling into question the idea that the planet might once have been Earth-like with an ocean of liquid water.

The team re-mapped Ovda Fluctus using radar data and discovered that the flow is not granitic as was expected from its location, but is more likely made up of basalt rock which can form with or without water.

The result has potentially significant implications for the evolutionary history of Venus.

“We know so little about Venus’ surface,” Dr. Treiman said.

“If the Ovda Regio highlands are made of basaltic rock as is most of Venus, they were likely squeezed up to their current heights by internal forces, possibly like mountains which result from plate tectonics on Earth.”

The research was published in the Journal of Geophysical Research: Planets.

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Frank B. Wroblewski et al. Ovda Fluctus, the Festoon Lava Flow on Ovda Regio, Venus: Not Silica-Rich. Journal of Geophysical Research: Planets, published online August 9, 2019; doi: 10.1029/2019JE006039