One of the most intriguing planetary bodies of interest astrobiologist is Europa, one of the moons of Jupiter. Europa is the smallest of Jupiter's Galilean and satellites. These are the four moons that were discovered, by Galileo Galilei in 1610. Europa is slightly smaller than our own moon, just over 300 kilometers in diameter. It orbits around Jupiter every three and a half days. The moon is tidally locked, and what that means is, one phase, it's always pointing towards Jupiter, on one hand, its surface is always pointing away. And it feels the gravitational effect of other moons, also Jupiter. These gravitational influences causes the moon to buckle as it's tidely distorted by these immense forces.
Most of what we know about Europa is from flyby missions. For example, Pioneer 10 and 11 in 1973 and 1974 took the first close-up images of Europa. And then in 1979, the Voyager 1 and 2 spacecraft destined to eventually leave the solar system, also took detailed images of the surface of Europa and saw an icy crusty surface and this prompted the first discussions on the possibility of a subsurface liquid ocean.
Galileo probe in 1995 took some of the closest to most detailed flyby photographs in the surface of Europa revealing some of its fine features, revealing cracks of fractures and chaotic terrains that have intrigued scientists . In 2007, the New Horizons probe that's destined to reach Pluto in 2014, also took images of the surface of Europa. These images taken by previous spacecraft have allowed to look at the surface and try and understand the composition of Europa and its internal structure. The surface of Europa is crisscrossed by dark lines.
It's a very bright surface and it has very few craters from asteroid and comet impacts, and this suggests that the surface of Europa is very young, at least relatively geologically. Young and constantly being resurfaced. What causes these barrens across the surface of Europa and one theory is that they're cased by warm ice rising up above the surface of the Europan crust and causing the crust to break apart and forming these lineations across the surface of Europa. Other chaotic terrains that look surprisingly like chunks, if you will, of icebergs moving around. Not quite in that way, but they suggest the surface of Europa is very young and is constantly being reformed. It's not known at the current time how thick the Europan ice shell is. It could be a few tens of kilometers. It could be hundreds of kilometers. Recent evidence suggest there may even be liquid water very near the surface of Europa.
The fractures that observed on the
surface of Europa are probably created by
the force of Jupiter pulling on Europa,
its fast gravitational force.
Expect the fractures to form a
very predictable pattern if they were just
very basic geological features from ice
cracking, but they've become increasingly
different from what would expect the
older they are.
And this would make, makes sense if the
interior of the planet was rotating faster
than the exterior.
What that suggests therefore is that the
core of Europa is detached from the icy
surface and that might be by liquid water
ocean.
There's other evidence for a water ocean
as well.
The saltiness in the ocean perturbs the
magnetic field of Jupiter and this is
evidence that's been picked up by studying
Jupiter's magnetic field around Europa.
This type of evidence also suggests that
Europa has a salty ocean inside it.
The inside of Europa may have a metallic core, surrounded by a silicate mantle, a mantle essentially of rocks, and then, a liquid ocean over that core, and then finally, a solid icy crust on the surface, which is what we see with orbiting spacecraft.
The possibility of liquid water has made
Europa one of the main targets for search
extraterrestrial life and its
possible that life inside Europa might
look something like we observe in deep
ocean beds, the bottom of the Earth's
oceans.
Of course, Its unknown what the
chemistry inside the Europan ocean and
what the conditions are on
the surface of that silicon core at the
bottom of the oceans.
There has been some controversial work
suggesting that radiation hitting the icy
surface of Europa could produce free
oxygen which could seep down into the
ocean, and some people have even
speculated on the possibility of complex
life inside the oceans of Europa feeding
off this oxygen and gaining energy from
the respiration of oxygen with other
compounds.
Well, all of these speculations
are very interesting.
They certainly fire the imagination of
astrobiologists and the public alike.
But need to know much more about the
chemistry of the Europan ocean in order to
assess the habitability of this plant.
Future missions already been planned to
take a closer look at Europa and Jupiter's
other moons. The Jupiter Icy Moon Explorer, JUICE,
which is being developed by the European
Space Agency will explore Jupiter's moon
and take a closer look at Europa.
Here is a fanciful image showing a possible mission to explore the oceans of Europa. In this case, the craft has melted its way through the Europan ice sheet and has sent out a small probe to explore the bottom of Europa's oceans. These, of course, would be extremely challenging missions to implement technically. But they show you some visions of the possible astrobiological future of the exploration of this fascinating moon.
Most of our knowledge of the moon is from
flyby missions.
The surface of Europe is young, it's icy
and it's actively deforming.
Europa gains its heat from tidal
interactions that cause the buckling of
the moon, generating heat and that's
melting that ice in contribution to the
formation of that deep Europan ocean.
There may be a liquid water ocean under
the ice and further investigation will
determine if anything lives in this
subsurface ocean.
So we can see that Europa is an example of
a moon with the subsurface icy ocean of
great interest astrobiologist and future
exploration.