The exploration of the outer Solar System has revealed a plethora of amazing worlds, the likes of which were little known or even unheard of just a decade ago. Among the most remarkable and tantalizing discoveries are the “ocean moons” such as Europa and Enceladus, which have oceans or seas of liquid water beneath their icy surfaces. Other moons like Titan, Ganymede, and Callisto may also have them, and even some asteroids. Titan also has seas and lakes of liquid methane/ethane on its surface. With all that water, these small worlds have become a primary focus in the search for possible life elsewhere in the Solar System. Now, a new NASA budget proposal wants to take that a step further and fund new missions to these watery moons.
For over a decade, scientists have been curious about the long fractures on Europa’s icy surface and the darker-coloured material they contain, as well as other relatively young geological features which are also coated with the mystery dark stuff. Now, researchers have come up with an explanation which not only provides an answer, but suggests that the moon’s subsurface ocean is able to interact with the surface as well as the rocky interior: the dark material is sea salt. Plus, a proposed squid-like robotic probe might actually explore that alien salty ocean one day…
Jupiter’s moon Europa, with its subsurface ocean, is considered by many to be the best place in the Solar System to search for extraterrestrial life. With NASA now committing itself to a new mission sometime in the 2020s, the focus is turning to what would be the best strategy for looking for any life which may be there. Over 200 scientists and engineers met at NASA’s Ames Research Center in Mountain View, Calif., last week for a workshop called The Potential for Finding Life in a Europa Plume to do just that.
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.
For decades, Jupiter’s moon Europa has been the focus of fascination and debate. Why? Because it has a global ocean – a deep, salty ocean similar to those on Earth, except that in Europa’s case it is always covered by a crust of ice. Speculation has grown that there could be life of some kind in that alien watery darkness, and now there is a new proposal for how to look for it – a tiny submarine!
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.
These are a couple of great images from many years ago, taken by the Voyager 1 spacecraft as it passed Jupiter. The first, in dramatic black & white, shows the moon Europa (with its subsurface ocean) passing in front of Jupiter’s turbulent clouds below, including the Great Red Spot on the left. It kind of looks like a Van Gogh painting, but it’s very real.
As one of the few places in the solar system other than Earth known to have an ocean, Europa has become one of the most fascinating worlds that we know of. This moon of Jupiter is small, but enticing – beneath its frozen surface of ice is a global ocean of water, making it a primary focus of study, especially in terms of the search for life elsewhere.
Jupiter’s moon Europa is often referred to as a “waterworld,” and for good reason: a global ocean almost definitely exists below its outer icy crust, making it a primary focus of interest in the search for life elsewhere in the solar system. So far, most of the information we have about this fascinating moon has come from flybys of the Galileo and Voyager spacecraft; these missions have been invaluable, of course, although limited. If we want to learn more about what is going on below in the Europan ocean, it will require new spacecraft with the necessary instruments to carry out long-term studies. Budgets are tight for an orbiter or lander, but a newly proposed “clipper” mission may just fit the bill.