Venus is covered in volcanoes, but are they active today? Although the surface is hidden from view by a thick layer of sulphuric acid clouds, these clouds themselves may provide the answer.

The sulphuric acid clouds are formed, essentially, from Sulphur Dioxide - SO2 - and water vapour; the only natural source of sulphur dioxide on Earth is from volcanoes, so its high abundance in the atmosphere of Venus is suggestive of active volcanism within geologically recent times - but this still does not answer whether the volcanoes are active today.

This film follows Thérese Encrenaz, from the Paris Observatory, as she maps sulphur dioxide and water vapour in the upper atmosphere of Venus. These turn out to show surprising variability - the sulphur dioxide abundances, in particular, exhibits large plumes, or regions of heightened abundance.

Our film next takes us to Brussels, where Ann Carine Vandaele and colleagues have been using solar ocultation from Venus Express to map the vertical profiles of SO2 abundances. Through these and other Venus Express measurements over the past decade, as combined with previous observations, reveals a pattern of sharp rises in SO2 abundances followed by gradual decreases over many years. This too suggests episodic injection of SO2-rich air from below the clouds.

Finally, the film concludes with Colin Wilson of Oxford University discussing Venus Express near-infrared surface observations of the surface of Venus. These revealed unusually black surface materials near known volcanoes, consistent fresh unweathered lavas. On one occasion the surface map showed a sharp increased in emission and subsequent cooling off, from a small region in a rift on the flanks of a large volcano which might be the first detection of a hot lava flow. Only one such event was conclusively identified from Venus Express observations, but future missions are planning to include cameras optimised for this observation type, so that the rate of present volcanism can be established.