Volcanic Activity on Io

This week’s guess the planet image comes from the outer solar system. It shows a volcanic explosion on Io, one of Jupiter’s moons. This image was captured by the voyager 1 spacecraft in 1979, credit for this image goes to NASA. This observation was very significant, because it shows activity taking place on another solar system body, something which had not been seen before. The volcanism seen here isn’t a relic of bygone processes, it was happening as the spacecraft flew by, and volcanism on Io continues to this day.

Geological activity comes in many forms, volcanism being one of the most extreme and spectacular. We are familiar with a huge variety of geological processes from studying the Earth. On our home planet we can watch these processes in action, and see how they shape the environment. One of the key principles of geology is that, on the whole, the landscape was shaped by the same suite of processes that continue into the present day. Some processes might have been more extreme in the past, such as the action of ice during glaciations, but glacial erosion is still at work across the planet. Thus by seeing how geological processes work in the present we can form theories about how they might have occurred in the past, and how they will continue to do so in the future. 

We can interpret the landscape based on the processes most likely to have formed it, and this tells us a lot about the environment of the past. By extension this understanding of geology in action allows us to speculate about the environments of other worlds. If we can see the characteristic signs of processes such as volcanoes or glaciers, so we know that volcanism and glaciations have taken place at some point. 

Often we can see the signs of past changes to the environment; Solidified lava flows, volcanic cones and other signs of volcanism have been observed on various solar system bodies, but many of them seem to be quite old. We don’t know for certain whether these processes continue to occur, only that they once did. Environmental conditions can change massively, both over time and from one region of the solar system to another. This can cause the end results of some familiar processes to not look quite as similar as we would like. When we see activity we know that the processes still occur, and this tells us a lot about the environment. 

Our observations of the Earth are extremely comprehensive, since we have a vast number of instruments and geologists on this planet. However the other worlds of the solar system are far less easy to study. Some, such as Io have only been visited a few times, and so our observations are somewhat fleeting. This means that signs of activity aren’t always easy to spot. We have to infer a lot from relatively little evidence. Sometimes features, such as cones, could have formed through multiple processes. If we don’t know precisely when or how they formed it would be possible to draw the wrong conclusions about the environment and the processes which shaped them. This makes images like this all the more amazing. On Io we can see that volcanism is current, and so this verifies our interpretation of the landscapes of this moon.

So why does Io still have active volcanoes when many other planets and moons seem not to? Io is very small, and so it is unlikely that it would still have internal heat under normal circumstances. However its proximity to Jupiter causes substantial tidal forces on the moon. The tidal pull of Jupiter’s gravity varies as Io moves closer and further from the larger planet. This causes heating of the interior through friction, keeping large parts of the moon molten and resulting in volcanic eruptions at the surface. A moon of a similar size, which didn’t orbit as large a planet, would not be expected to be as geologically active. 

Planetary scientists look for signs of activity all across the solar system, as they have the power to verify our theories about how planets and moons formed, and how geological processes continue to shape them in the present day. 

Image Credit: NASA Planetary Photojournal