Venus has lava tubes, and they’re weird

We now know for sure that massive underground tunnels, carved by lava, exist on Venus – and they are surprisingly wide and different from those on any other planet.

It is uncontroversial that lava tubes – underground tunnels carved out by molten rock – exist on Earth, the moon and Mars. Smaller planets with low gravity tend to form more cavernous tubes, in part because the rock walls are less likely to collapse with weaker gravity. On the moon, for instance, the tubes are so large that scientists have proposed using them as live-in shelters for astronauts, providing shielding from the harsh solar wind.

Scientists had seen hints of these lava tubes on Venus, from holes and pits that appear to have formed on its surface, but it was unclear whether these were caused by lava tubes beneath them or by other geological processes, such as from an active fault line.

Now, Barbara De Toffoli at the University of Padova in Italy and her colleagues have found direct evidence of lava tubes on Venus. They also appear to be surprisingly wide and of a comparable volume to those on the moon, despite Venus being more like Earth in terms of its mass and gravity.

“Earth lava tubes have smaller volumes, Mars tubes have slightly bigger volumes, and then the moon’s tubes have even bigger volumes – and then there’s Venus, completely disrupting this trend, displaying very, very big tube volumes,” De Toffoli told the Europlanet Science Congress in Helsinki, Finland, earlier this month. “This is already giving away the fact that there’s likely something more on Venus playing a significant role.”

Using radar and mapping data from past missions, De Toffoli and her team analysed how these pits lined up and were arranged near large volcanoes. They found four clear examples that didn’t have any alternative geological explanation, like tectonic activity. The pits also lined up with the steepest part of the volcanoes’ slopes, which is the direction the lava would have travelled, and the ratio of their depth and width was consistent with other known lava tubes.

The tubes’ unexpected size, in particular their width, suggests that the extreme Venusian environment, which is very hot and high pressure, might affect how molten rock moves under its surface, said De Toffoli, and isn’t just dependent on gravity like lava tubes on other planets. “Due to the very high pressure, there’s an overall flattening out of the tubes, instead of having a very intense erosion at the floor that usually happens on other planets.”