Hi everyone. As you know, last time we took a look at 10 things you wanted to know about Enceladus. As promised, this time, we’re considering some of the things you might find interesting about another of the moons mentioned in that article, Europa.
1. What do we know about Europa?
Europa is the 6th closest moon to Jupiter and the smallest of its 4 Galilean satellites. Nonetheless, with a diameter of 3100 km (1900miles) Europa is only slightly smaller than our own Moon, making her the 6th largest moon in the solar system.
2. What is Europa composed of?
Europa is very interesting. She is comprised of silicate rock over an iron core, and has a tenuous atmosphere which is mostly oxygen. From recent findings, it would appear a liquid ocean lies beneath a thick ice crust. Note: So dense is this ice, that it displays the hardness of granite.
3. How was Europa discovered?
Europa was discovered on 8th January 1610 by Galileo Galilei. It is named after a Phoenician noblewoman in Greek mythology, Europa, who was courted by Zeus and became the queen of Crete
4. Are there any cool facts we need to know?
There certainly are. Europa’s surface is one of the smoothest in the solar system when considering the lack of large-scale features such as mountains or craters. Although striated by cracks and streaks, these are what appear to be albedo features, (areas that show a sharp contrast in brightness and darkness), and which emphasize regions of low topography.
5. So what are the Lineae?
Europa’s most striking features are a series of dark streaks crisscrossing the entire globe. These are called Lineae, and they pose a bit of a mystery to astronomers. Why?
Scientist surmised the Lineae were produced by a series of eruptions of warm ice as the Europan crust spread open to expose the warmer layers beneath. (Much like the effect seen within Earth’s oceanic ridges). But, the fractures could also have been caused by tidal flexing exerted by Jupiter.
You see, because Europa is tidally locked to its parent planet, and always presents the same approximate orientation toward her, the stress patterns should form a distinctive and predictable pattern.
However, only the youngest of Europa’s fractures conform to that pattern. The others appear to occur at increasingly different orientations the older they are. This could only be explained if Europa’s surface rotates slightly faster than its interior. This is what first led scientists to suspect the existence of a subsurface ocean, as such a body would “uncouple” the surface from its rocky mantle, and the effects of Jupiter’s gravity relentlessly tugging on the outer ice crust.
6. That must mean the interior is rather interesting?
And it’s a subject of much debate.
It is believed Europa has an outer layer of water around 100 KM (62 miles) thick: Some as a frozen ice upper crust, and the rest as liquid ocean below the ice. Recent magnetic field data from the Galileo Orbiter showed that Europa has an induced magnetic field through interaction with Jupiter’s magnetic field. This would tend to suggest the presence of a subsurface conductive layer – likely a salty liquid water ocean. Portions of the crust are estimated to have undergone a rotation of 80⁰ – which supports the presence of a water ocean, as this would be highly unlikely if the ice were permanently attached to the mantle.
7. And what about the atmosphere? Oxygen?
Observations with the Goddard High resolution Spectrograph of the Hubble Space Telescope in 1995, revealed Europe has a thin atmosphere mostly comprised of molecular oxygen. But – there’s a but! The surface pressure on Europa is too low for the moon to generate its own atmosphere. So, how can it have one?
Aha! In 1997, the Galileo spacecraft confirmed the presence of a tenuous ionosphere (an upper layer of charged particles) around Europa created by solar radiation and energetic particles from Jupiter’s own magnetosphere. So, unlike Earth’s atmosphere, Europa’s oxygen is not of biological origin. Cool or what?
8. So how does the atmosphere form?
Europa’s surface-bound atmosphere forms through a process called radiolysis (the disassociation of molecules by nuclear radiation) Yes, the high energy flux involved in this process cleaves the chemical bonds keeping certain molecules in place, and allows some of them to create a thin atmosphere. Super cool!
9. Does the presence of water mean closer examination?
You bet. That subsurface ocean has scientists excited. The orbiter element is being looked at to concentrate of further studies of the ocean itself. Other projects are planned to look into the chemical composition of the atmosphere, surface, and energy within Europa’s localized region. Funding is also being sought to explore the “habitability” of Europe itself, or at least, the exploration of sites for future landings. Other projects seek to characterize the extent of the ocean – especially in relation to its deeper interior.
10. Its life Jim, but not as we know it!
So why all the interest in this moon, so far, far away?
Ha! That’s easy. Europa has now emerged as one of the top locations in the Solar System for potential extraterrestrial life and habitability. It really is possible that life exists under the ice ocean, similar to what we find here within Earth’s deep-ocean hydrothermal vents.
You see, we used to think that life was dependent on energy from the sun. After all, plants capture sunlight to photosynthesize sugars from carbon dioxide and water. In the process, they release oxygen. The plants are then eaten by animals who pass the energy up through the food chain.
But, in 1977, the deep-sea exploration submersible Alvin, working in the Galapagos Rift discovered colonies of giant tube worms, clams, mussels and other crustaceans clustered around undersea volcanic vents known as black smokers. Despite the fact these creatures had no direct access to sunlight, they were thriving. That’s because they were using a form of bacterium as a basis for their food, which derived its energy from the oxidization of reactive chemicals (hydrogen & hydrogen sulfide) bubbling up from the Earth’s interior.
This discovery revolutionized the study of biology, as it confirmed life does not need to be sun-dependent. It also opened up whole new vistas of astrobiology by expanding the number of possible extraterrestrial venues.
Obviously, Europa is very different from the Earth. Nevertheless, the findings at the bottom of the Galapagos Rift provide a possible model for life in Europa’s ocean. Why?
The energy provided by tidal flexing drives active geological processes within Europa’s interior several magnitudes greater than any energy she might derive from any internal radiological source. Therefore, it is entirely possible that life may be clustered around similar hydrothermal vents, either on or under Europa’s ocean floor.
Another theory propounds life might exist clinging to the lower surface of Europa’s ice layer, much like the algae and plankton found in Earth’s Polar Regions.
More food for thought was provided in 2011 when a team or researchers presented evidence in the scientific journal, Nature, suggesting the existence of vast lakes of liquid water. These bodies were thought to be entirely encased in Europa’s icy outer shell and therefore distinct from the ocean. If confirmed, these lakes could be yet another potential habitat for life.
Another clue is provided by the fact that hydrogen peroxide is abundant across much of the surface of Europa. If the surface peroxide mixes into the ocean below, it could be a vital energy supply for simple forms of life. Scientists think hydrogen peroxide is an important factor for the habitability of the global liquid water ocean under Europa’s icy crust because hydrogen peroxide decays to oxygen when mixed into liquid water.
Whatever the case, future exploration is bound to follow, and when it does, I have the feeling we’ll be astounded by what we find.
Next time, we’ll return to a place that we’ve visited in this series before. Mars. I thought it might be a good idea, because, if we’re going to visit such faraway places as Europa, a stop off point might be a base on a planet that we’ll more than likely visit in the not too far distant future. But what would visiting Mars entail? Aha! For that, you’ll have to wait.
Until then – have a great day.