Learn about the origin and evolution of life and the search for life beyond the Earth.
Enceladus
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From the course by The University of Edinburgh
Astrobiology and the Search for Extraterrestrial Life
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From the lesson
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?
Meet the Instructors
Charles CockellProfessor
Astrobiology
[BLANK_AUDIO]
One planetary body that has really fascinated astrobiologists is
Enceladus, the tiny moon of the giant gas planet, Saturn.
Here's some basic facts about Enceladus.
It was discovered in 1789 by astronomer William Hershel.
It's over a billion kilometers away from the Earth.
It seems to have a water-ice surface, a
little bit like Europa, hence the interest from astrobiologists.
And it orbits very
close to Saturn and its rings, which makes it very difficult to view from the Earth.
It's a tiny little moon, about 500 kilometers in diameter, much
smaller than the Earth, much smaller than even our own moon.
Like Europa, much of our knowledge of
Enceladus has been gathered from fly-by missions.
In 1980 to 81 the Voyager one and two spacecraft gave us
the first images and information on the nature of this tiny moon.
And what did it tell us?
Well Voyager saw a highly reflective surface with few impact craters and told
us that Enceladus probably had an icy surface that's also very young and active.
It discovered a very heavily cratered mid-high northern latitude and
lightly cratered region close to the equator, that gives us
some idea of the differences in the composition of the
ice and its age across the surface of the moon.
It also found that Enceladus
is embedded in the densest part of one of Saturn's rings, the E ring.
And it's thought that Enceladus may be contributing material to
the production of this ring as we'll see in a bit.
The chief conclusion from what we observe with Voyager is that Enceladus is a young,
geologically-active moon possiby feeding the E-Ring of Saturn.
Many questions about Enceladus began to
be answered with the fly-bys by the Cassini spacecraft beginning in 2004.
It returned some of the best resolution images we have of Enceladus.
But there's little doubt in saying this most remarkable
discovery was that there are plumes containing hydro-carbons and
water being injected from the South Pole of Enceladus
and we'll come back to those in a little while.
Let's have a look at some of the
interesting features that have been observed on the
surface of Enceladus.
First of all, Cassini spacecraft confirmed this is a
moon with a very young surface, a very active surface.
Different levels of cratering were found in different areas, but all craters show
signs of deformation and degradation suggesting an
icy surface where the craters are collapsing.
And beginning to subside and dissipate in this active surface.
Near the south pole of the moon are features that have been called
tiger stripes, which may be as young as a half a million years old.
Which is very young in geological terms.
They seem to have a different composition from the rest of Enceladus.
They contain coarse ice grains instead of fine grains and
lots of organics seem to be present in these tiger stripes.
There's little doubt in saying that the most remarkable discovery was these vapor
plumes being ejected from the tiger stripes from the south pole of Enceladus.
The Cassini spacecraft had the opportunity to
fly through these plumes and measure their composition.
And it found some extraordinary things.
It found that these plumes contain water, water ice.
It also found methane, carbon dioxide, and organic compounds.
Compounds such as propane, ethane, acetylene
and also more complex organic compounds.
In fact, the instrument, the GCMS on this spacecraft, was
not adequate to identify these very complex organic compounds because
it wasn't designed for this task, they weren't expecting to
find hydro carbons in these plumes being ejected from Enceladus.
But these complex materials,
these complex organics, suggest that the interior of
Encedalus contains liquid water, and might be acting
as a huge chemical reactor, producing organic compounds
that are being ejected into space in these plumes.
And one obvious question for astrobiologists is could
these complex organic molecules indicate life within the moon?
And even if there is no life in Enceladus,
perhaps these complex organic compounds can tell us something
about the reactions, the chemical reactions that are necessary to
build the building blocks of life, to create the building
blocks of life that are necessary for the evolution of
life on planetary surfaces or in the interior of planets.
All of these data come together to give
us clues to the interior structure of Enceladus.
We think that Enceladus contains a rocky core
surrounded by a water ice mantle but the
tidal heat generated the gravitational force of Saturn
causes the buckling of this moon that generates heat.
This heat might melt the water ice mantle beneath the surface creating pressurized
bodies of liquid water.
These pressurized bodies of liquid water then
reach the surface where they break out
through the tiger stripes and create these
plumes ejecting these complex organic materials into space.
A forthcoming challenge of astrobiology is to determine the composition of possible
liquid water beneath the surface of
Enceladus, and what these organics really mean.
Could this be a location for extraterrestrial life or
just an interesting factory for organic compounds.
Future missions to Enceladus are already being planned,
the Titan-Saturn system mission has been proposed by
NASA and the European Space Agency, and it's
a proposed mission to study Saturn's moons, including Enceladus.
It lost out on funding in a mission to Europa, but nevertheless,
there will be missions to Enceladus to explore those plumes to see
what they contain and to see whether they might reveal something about
the interior of Enceladus whether it could even be a location for life.
So what have we learned in this lecture?
We've learned that Enceladus is a tiny moon of Saturn.
It has a young, actively deforming surface.
Most importantly for astrobiologists, we've learned that it's spewing
out jets of water vapor and organics into space.
And it's thought that Enceladus might
have salty water beneath the surface, that's providing the source of water
for these plumes, it could even be a location to search for life.
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