Venus ‘once had oceans of water’

Venus was once much more like Earth than thought, with oceans of water and drifting continents, new results from an orbiting space probe suggest. The second planet from the sun has been called Earth’s evil twin because it is so hot and dry that it resembles hell.
New Venus Express map of southern hemisphere

Planetary scientists say its climate went out of control. They are keen to know why in case the same thing happens to our own world.

Venus is completely shrouded in clouds, causing its atmosphere to act like a greenhouse trapping heat. Now Europe’s orbiting Venus Express probe has used mapped a large chunk of the planet using a cloud-piercing infrared camera.

The results support previous suspicions that Venus has ancient continents produced by volcanic activity and which used to be surrounded by seas of water.

Previous maps of Venus have been produced by radar. The new infrared chart of the planet’s southern hemisphere, built up from thousands of individual images, is the first to tell scientists what the rocks might be made of.

Different types of rock radiate different levels of heat, in a similar way to how a brick wall gives off warmth at the end of a hot day. The measurements for the new map, made with the Visible and Infrared Thermal Imaging Spectrometer, were similarly made of the night side of Venus.

Eight Russian probes which landed on Venus in the 1970s and 1980s discovered they were sitting on basalt rock in the few moments before they were crushed by the incredible weight of the planet’s poisonous atmosphere. The surface was twice the maximum temperature inside a domestic oven.

But the Venus Express map shoes lighter, old rocks on high plateau called Phoebe and Alpha Regio. Experts say that, on Earth, such light-coloured rocks are usually granite and form continents.

Granite is formed when ancient rocks, made of basalt, are driven down into the planet by shifting continents, a process known as plate tectonics. Water mixes with the basalt to form granite and the mixture is reborn through volcanic eruptions.

Venus Express scientist Nils Müller, of Germany’s Münster University, said: “If there is granite on Venus, there must have been an ocean and plate tectonics in the past. 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.”

He added: “Venus is a big planet, being heated by radioactive elements in its interior. It should have as much volcanic activity as Earth.”

The European Space Agency report does not say when Venus had oceans, but it seems clear that we must be talking many millions, or billions, of years ago. Some areas of darker rock already hint at relatively recent volcanic flows. Space scientists are keen to send a new lander to Venus to find out more.

Picture: The new infrared map of Venus is centred at the South Pole. The measured temperatures range from 442°C to 422°C (or 695K) blue. (Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA)

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