Surface temperature readings from Venus suggest the planet has had active volcanoes some time in the last 2.5 million years, researchers say.

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Heat data from the Venus Express orbiter is overlayed as colours on a 3-D plot of the surface of Venus to show a volcanic peak that's bright in infrared radiation. ((NASA/JPL-Caltech/ESA))

The observations are the first to suggest that Venus may be a geologically active planet.

Researchers combined surface heat data from instruments on the European Space Agency's Venus Express spacecraft, in orbit around the planet since April 2006, with radar data from NASA's Magellan mission from the early 1990s.

They found infrared evidence of lava flows on Venus in three volcanic hotspots that were between a few hundred years and 2.5 million years old.

Jet Propulsion Laboratory researcher Sue Smrekar said the Magellan mission gave hints of volcanic activity on Venus, but didn't indicate how long ago it occurred.

"We had data on the Magellan mission to Venus … that showed areas that look very much like Hawaii, geologically speaking. They had broad topographic swells, volcanoes at the top and, most importantly, a gravity anomaly that indicated there was hot stuff deep down on the inside," Smrekar told CBC Radio's Quirks & Quarks.

The low-density material, called a mantle plume, pushes up the surface by 1,000 kilometres or more, and melts material in the planet's crust, causing volcanoes, Smrekar said.

The lava flows at the three hotspots emit slightly more heat when compared with the surrounding terrain.

"The temperature variations we're looking at are very small, only a few degrees, but those few degrees tell us that there's a difference in the composition from one place to another on the surface of Venus," Smrekar said.

Data indicates rock is relatively young

Smrekar said this indicates that the rock is relatively young and hasn't experienced much degradation from the harsh weather on Venus.

"The thermal band is sensitive to minerals and their iron content, so what we're looking at are minerals that have more iron content than the rest of Venus," said Smrekar.

"The reason that tells us they're fresh material is that once lava flows erupt on the surface of Venus, they start interacting with the atmosphere right away. Those iron minerals break down or weather as they interact with the atmosphere," she said.

The weathering is similar to what happens on Earth when iron is exposed to the atmosphere, but it's a much stronger process on Venus because of the harsher conditions there.

The surface temperature of Venus is hot enough to melt lead and its atmospheric pressure is 90 times greater than that on Earth. The planet's atmosphere also contains much more carbon dioxide and sulphur dioxide than Earth's does, and both gases react with iron.

If there are active volcanoes on Venus, the planet would join Earth and Jupiter's moon Io as the only confirmed volcanically active bodies in the solar system.

There is some evidence of recent volcanic activity on Mars, although it isn't conclusive.