Jupiter has often been referred to as the King of Planets, and for good reason, as it is a massive gas giant, much larger than Earth and the largest planet in our Solar System. It is more than 2.5 times as massive as all the other planets combined, and is a mesmerizing world of colourful bands of clouds wrapping around the globe, which can be seen even in a small telescope, but exhibit incredible detail when seen by spacecraft. Jupiter is also itself the center of a sort of miniature solar system, with dozens of moons orbiting around it. We’ve seen this world up close before by spacecraft such as Voyager and Galileo, but now a new visitor has arrived in the Jovian system: NASA’s spacecraft Juno.
Europa has been in the news a lot this past week, with the discovery of apparent plumes of water vapour erupting from its surface, similar to those on Saturn’s moon Enceladus. An exciting find, given that this moon has a global ocean of water covered by its icy crust. There was also the first detection of clay-type minerals on Europa’s surface. Now, another discovery shows that Europa may be similar to Earth in yet another way – the first other known world to have active plate tectonics, it was announced last Friday at the American Geophysical Union meeting in San Francisco.
Why is this significant? Plate tectonics can provide a way for nutrients to be carried from the surface down into the waters below, just as they do on Earth.
According to planetary scientist Alyssa Rhoden, a NASA postdoctoral program fellow, “What’s exciting is that this would be the only other place outside of Earth where a plate-tectonic-style system is occurring.”
Scientists have known for some time that Europa has a relatively young surface which is being replenished somehow by new, fresh ice. It is thought that this ice is coming up through features called dilational bands, which are long cracks on the surface. There are thousands of them, making Europa look like a giant cracked eggshell. The new ice also keeps Europa’s surface remarkably smooth with very few craters.
New studies now suggest that the dilational bands behave in a similar way to Earth’s tectonic plates. New ice rises up through the cracks to the surface, but where does the old ice go?
Planetary scientist Simon Kattenhorn of the University of Idaho explained what they think is happening during their presentation for the AGU meeting:
“Unless Europa has been expanding within the last 40 to 90 million years, there has to be some process on this icy moon that’s able to accommodate a large amount of new surface area being created at dilational bands.”
That process would be similar to what happens along mid-ocean ridges on Earth, where crustal tectonic plates meet together. New crust, or in Europa’s case, ice, is forced upward through the spaces between the plates where it forms newer crust. Older crust in turn is then forced back down into the Earth’s mantle in places where a continental plate meets an oceanic plate. In this process, called subduction, the oceanic plate is pushed below the continental plate. This whole exchange is an efficient global recycling between old and new material.
Now for the first time, what appear to be subduction zones have been identified on Europa as well, by Kattenhorn and his colleagues. This is important, since organic material, also just found on Europa’s surface for the first time, and nutrients could then have a way of making it down below the surface and into the water deep below. This of course has a direct bearing on the possibility of life in Europa’s ocean. Minerals necessary for life are likely present on the rocky ocean bottom as well since the rocky mantle is thought to be in direct contact with the ocean water just like on Earth.
There may still be another explanation for the observations, but this and other evidence continues to show that Europa is a geologically active little world instead of just a frozen ice ball as once believed. And maybe, just maybe, a living one as well.
This article was first published on Examiner.com.
Europa has intrigued people for decades, ever since the first evidence was found that this small icy moon of Jupiter harbours a subsurface ocean. Additional information about the actual conditions below the surface have been difficult to obtain, since this ocean is covered by a global crust of ice perhaps ten of kilometres thick in places. But perseverance pays off, and now in just this past week there are two new significant discoveries being talked about – evidence from the Hubble Space Telescope for water vapour plumes, announced on Thursday, erupting from Europa’s surface similar to those on Saturn’s moon Enceladus, and the first detection of clay-type minerals on the surface, announced on Wednesday.
The impact of comet Shoemaker-Levy 9 into Jupiter in 1994 was a spectacular event for astronomers. The scars in Jupiter’s atmosphere lasted for weeks afterward; while those have long since faded, there are still other features of the impact visible even now, it was announced last Tuesday.
Europa is a fascinating little world, a moon with an icy crust and a subsurface global ocean. The environment is similar to the ice-covered waters at the Earth’s poles. Now scientists think that there may be another feature which is also found on Earth – huge frozen spikes of ice on the surface.