Venus is a rocky world that is similar in size to Earth, but it’s also a world that remains mysterious because it’s permanently shrouded in cloud. In the 1990s, NASA’s Magellan mission used radar to pierce the clouds and map the planet’s surface, revealing a landscape covered with volcanoes.
Crater counts suggest none of the surface is more than about 750 million years old, but we don’t know over what timescale it was laid down. Radar tells us the topography and elevation of the surface, revealing that there are higher mountains which are cone-shaped, like a typical volcano.
It also allows us to differentiate terrain types and shows features that are consistent with the presence of volcanoes, such as lava flows. But what it does not tell us is whether or not those volcanoes are still active.
Cytherean satellite
ESA’s Venus Express satellite has been orbiting the planet since 2006. Most of its instruments focus on the atmosphere, but some can see right down to the ground in infrared wavelengths and we are seeing the hot glow of the surface itself. One thing we are doing is simply looking for regions of high temperature, as you might find from a lava lake or a still-hot lava flow. A problem here is that the glow is scattered by the clouds, so we get a hazy picture instead of a pin-sharp one. We haven’t seen any lava lakes yet, but we’re still looking.
Apart from mapping minerals we can also look in detail at the atmosphere, which is where Venus Express excels. Compared to the surface of the planet, the atmosphere is more dynamic and changes more quickly, so we should be able to see alterations taking place on a shorter timescale.
In the short term, we can continue examining Venus Express data to look for lava flows and lakes, and try to make better sense of the sulphur dioxide signatures in the atmosphere to work out whether they are due to volcanic eruptions or weather patterns. In the longer term, we could send an orbiter with a new generation of radar technology to measure millimeter-scale changes in surface height. This would help identify active volcanism.
Ultimately, we’d like to send a rover to Venus to search for the suspected volcanoes – but it would need to be able to withstand the 450”C surface heat and enormous atmospheric pressure.