A volcano erupted on Venus in the 1990s!

Exciting news that there was a volcanic eruption on Venus in the early 1990s, shown by changes in the size of crater between two passes of the Magellan probe‘s radar over the same area.

There have been hints of volcanic activity observed before, but this is the first direct observation – even if it took 30 years to take note of it. According to the paper, about 42% of Venus was imaged two or more times during the Magellan mission, but the radar energy was bounced off the surface in different directions each time. This means that you can’t just automatically compare images – the different angles of reflection mean that things might “look” different even if nothing has changed.

Instead, this apparent eruption was found by manually searching data in an area considered likely to be volcanically active. The change in vent size and shape at the bottom right is pretty definitive, but the different viewing angles between the two images are the reason that the ‘new flows’ are labelled with a question mark – their appearance is suggestive but you can’t rule out the change just being due to the radar energy being scattered differently at a different incident angle.

It makes the case for a follow up mission to Magellan, that can be designed to make more easily comparable repeat observations, even more compelling. Unfortunately, the recently announced delay to NASA’s VERITAS Venus radar mapper mission is more of a ‘shut it down, and hope we can spin it up again in a few years without any further delays or cost overruns.’ I have some sympathy – the non human spaceflight part of NASA consistently gets the short end of the funding stick, and produces a lot of awesome science nonetheless – but this appears to be a pretty big screw-up that may mean the mission never happens at all. Which would suck – we need another radar mapper not just to hunt down more Venusian volcanoes, but because ‘what does Venusian plate tectonics (or not plate tectonics) look like?’ is a pretty fundamental question I’d very much like to know the answer to.

To put it another way, one of the biggest questions in planetary science is: why is Venus so different than Earth, despite their size, composition and internal structure being so similar? Answering this question might give us a hint about whether any “Earth-like” rocky exoplanets we discover are actually more likely to be like Earth, or whether they are more likely to be friends of our evil planetary twin.