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Europa
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Del curso dictado por The University of Edinburgh
Astrobiology and the Search for Extraterrestrial Life
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De la lección
Habitable Environments Elsewhere in our Solar System?
What are the prospects for life on other planetary bodies in our Solar System and how do we go about searching for it? What conditions are required for a planet to be habitable?
Conoce a los instructores
Charles CockellProfessor
Astrobiology
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One of the most intriguing planetary bodies of interest
to astrobiologists is Europa, one of the moons of Jupiter.
Europa is the smallest of Jupiter's Galilean satellites, these are
the four moons that were discovered by Galileo Galilee in 1610.
Europa is slightly smaller than our own moon just over
3000 kilometers in diameter it orbits around Jupiter once every
3 and a half days.
The Moon is tidally locked and what that means is that one
face is always pointing towards Jupiter
and one hemisphere is always pointing away.
And it feels the gravitational effects of other moons and also Jupiter.
These gravitational influences causes the moon to buckle
as it's tidally distorted by these immense forces.
Most of what we know about Europa is from fly by 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 sub surface liquid ocean.
Galileo probe in 1995 took some of the closest and
most detailed fly by photographs of the surface of Europa.
Revealing some of it's fine features, revealing cracks and
factures and chaotic terrains that have intrigued scientists since.
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 us to look at the surface
and try and understand composition of Europa and it's 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 the surface of Europa is
very young, at least relatively, geologically young and constantly
being resurfaced.
Well, my thoughts, what causes these barrens across the surface of Europe.
One theory is that they're caused by warm
ice rising underneath the surface of the Europan
crust and causing the crust to break apart
and form 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 have been
liquid water, very near the surface of Europa.
The fractures that we observe on the surface of
Europa are probably created by the force of Jupiter
pulling on Europa, it's vast gravitational force.
We would expect fractures to form a very predictable pattern
if they were just very basic geological features from ice cracking.
But they become increasingly different from what
we would expect, the older they are, and
this would make 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.
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 talk of evidence also suggests that Europa has a salty ocean inside it.
When we put all this evidence together, what we find is a model
that might look something like this.
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 space craft.
Now, of course, the question for astrobiologists, the most intriguing
question, is could there be anything living in the Europan ocean?
The possibility of liquid water has made Europa one
of the main targets in the search for extraterrestrial life.
And it's possible that life inside Europa might
look something like what we observe in deep-ocean vents.
The bottom of the earth's oceans.
Of course, we don't really know what the
chemistry is inside the Europan ocean and we don't
know what the conditions are on the surface of
that silica core at the bottom of the oceans.
It may not look anything like the deep sub-surface
of surface of Earth's oceans.
But by looking at life in deep crust of materials on the Earth, we might get some
ideas of the sort of life that we might at least look for inside a Europan ocean.
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, of course, all of these speculations are very interesting,
they certainly fire the imagination of astrobiologists and the public alike.
But we need to know much more about the chemistry of
the Europan ocean in order to assess the habitability of this planet.
Future missions were already being 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 moons 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.
So what have we learned in this lecture?
Well hopefully we've learned that Europa is a moon of Jupiter which
is a good candidate for life or at least exploring potential habitability.
Most of our knowledge of the moon is from fly-by missions.
The surface of Europa is young, it's icy, and it's actively deforming.
Europa gains it's heat from tidal interactions
that cause the buffing of the moon.
Generating heat and that's melting that ice and
contributing 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 a subsurface icy
ocean of great interest to astrobiologists and future exploration.
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