[BLANK_AUDIO]. Let's talk about some other interesting
places in the solar System where there could be life or at
least habitable environments. Now, one unusual place is the moon of
Neptune called Triton. Triton is an unusual moon because it
orbits backwards around Neptune. And this has led to the idea that maybe it
was a body That was captured by Neptune earlier in
the history of the solar system. Like Europa, it has an icy surface. But Triton seems to have a surface that
also contains nitrogen. Methane, carbon dioxide, carbon monoxide,
and other types of volatile compounds That have frozen down on to the surface of
the moon. But it's another example, of an icy moon
in the outer solar system. There are some parts of this moon that
have a lot Of impact craters, and that suggests that
those areas might be Quite old. But generally the surface of Triton seems
to be very young. And in fact there are locations on the
surface of The Moon where there seems to be active
geological processes. Particularly black colorations on the
surface that look like Nitrogen geysers erupting from the
subsurface of the moon. Suggesting some sort of cryo-activity
beneath The surface, where nitrogen is welling Up through fractures, and being ejected
onto the surface of the moon. So although the surface of Titan looks
like it has some activity today, generally Speaking the surface of the moon doesn't
look as active as, for example, Europa. But that might have been very different in
the early history of the moon. In the early history of the solar system,
it's possible that Triton was tidally Flexed, a bit like Europa, and it's
possible that in the subsurface Of that moon there may even have been a
subsurface liquid ocean. Is it possible that this moon was
habitable in its early history? Is it even possible today? There might be pockets of habitable Environments in the subsurface of the
moon.
Well, we don't really know enough about
Triton To be able to assess those ideas
accurately. But this is certainly another place in the
solar System where we might think about
searching for habitable Conditions, and a place that may even have
had Habitable conditions in the early history
of the solar system. And one could imagine studying the surface
of that Moon, looking at the compounds on the icy
surface. Perhaps even looking for five signatures
of life that Might have once lived in the subsurface of
Triton. So this is another example of a moon far
away From the sun that could have had habitable Environments because of tidal forces
within the moon. We talked a little bit about Europa,
perhaps one of the most compelling Locations to search for habitable
environments amongst The icy moons of the solar system. Another moon of Jupiter that might be
worth investigating is Ganymede. And Ganymede, Like Europa, also seems to have a
sub-surface liquid ocean. This is an image showing you a slice
through Ganymede and What we think the internal structure of
that moon looks like. It's probably got a metallic core
surrounded by a rocky inner mantle, Rocky core, silicate core around that
around the metallic core. And then beyond that, a shell of warm ice. And then just above that, a liquid water
ocean, and that ocean is trapped between That warm ice beneath it, and the icy
crust on the surface of the moon. A bit like the icy crust of Europa. So that liquid water ocean in Ganymede
could Also be another location where we could
look For habitable conditions, but there is one
problem With that ocean, and that's it's trapped
between Two layers of ice. Now as we saw earlier in this course, life
needs a lot of things to get going. It needs elements, it needs a source of
nitrogen and
Phosphorus and, and certain elements like
iron to do chemical reactions. An ocean that's in contact with a silicate
core, A rocky core like Europa, might be a much Better place for life, because it'll have
more of An enriched collection of, of elements and
potential nutrients and Even energy supplies for life. But an ocean that's trapped between two
layers of ice, might be Very limited in the quantities of
nutrients and elements that it has. So perhaps Ganymede isn't such a good
location To search for life as say compared to
Europa. But nevertheless, any environment in the
solar system where There's liquid water, could be a potential
habitable environment. So Ganymede is another Moon that we might look at as a potential
location for life, and if not life, then Perhaps some of the early chemical
reactions that might Suggest habitable environments where there
is potential for life. People have had even more crazy ideas
about the Possibility of habitable environments
around Pluto and its moon Charon. And in 2015 the New Horizons mission will arrive at Pluto
and give us some Ideas about the composition of that body
and also its moon, Charon. Is it possible that these bodies also have
subsurface oceans? Well, we don't know enough about them to Be able to speculate with any accuracy on
that. But we might even look for habitable
environments beyond the orbit of Neptune. And this just illustrates the remarkable
possibilities For liquid water habitats in our solar
system. We've looked at Europa, Ganymede, even the Moon of, of Neptune Triton, and possibly
we Might even look for habitable environments
in the Subsurface of bodies beyond that, Pluto
and Charon. But there is one moon that I want to
return to in this lecture and That is Titan, one of the moons of Saturn
in fact the largest moon of Saturn. It's an intriguing moon, and strangely
enough, when people
First looked at this moon, it didn't look
very interesting. This is an image of Titan, and you can see
that it's got This, this almost, this homogeneous haze
that covers the surface of this moon. It doesn't look like it has many
interesting features. But it turns out that this haze is a very
fascinating atmosphere. This haze is mixed, is a mixture Of nitrogen and hydrocarbons, methane, and
other Carbon compounds of great interest to
astrobiologists. And in fact, it's really the only place
beyond the Earth Where stable bodies of liquids exist on
the surface of that moon. What are these liquids and what are the
characteristics Of this moon that make it so interesting
to astrobiologists. Well, in 2005 the Cassini spacecraft let
go of the Huygens Lander, That traveled down to the surface of Titan
and sent Us back the first images of the surface of
that moon. And you can see an image here, a
remarkable image of The surface of Titan that was taken by the
Huygens Lander. What did it see? Well it saw what looked like rocks, and
you Can see these rocky formations on the
surface of Titan. But it turns out that these are not rocks
these are lumps of ice, solid water ice That behaves like rock at very low
temperatures To be found on the surface of Titan. But what it also found was landscapes made
of hydrocarbons, complex organic Carbons that forms from this complex
atmospheric process that occurs on Titan. You see, Titan has legs of liquid methane,
liquid methane And ethane that formed over the surface of
the moon. This methane evaporates into the
atmosphere of Titan, it rises up into The atmosphere, and then it reacts with
ultraviolet radiation from our sun. And that ultraviolet radiation causes the
methane To react and form complex, organic
carbons. That brown haze that you see in the
atmosphere of Titan is actually Complex organic material formed from the Reaction of methane and other organic
compounds
With ultraviolet radiation from the
sunlight. And these complex organic carbons rain
down to the surface Of Titan and form these landscapes of
complex carbon compounds. And that is what you're looking at here,
in this image taken By Huygens, looking out across the Surface of Titan, across these hydrocarbon
landscapes. Why is this so interesting to
astrobiologists? Well these complex organic reactions, Reactions of carbon compounds with
ultraviolet radiation, Might be the sort of reactions that
occurred On early earth that ultimately led to The evolution, the origin and evolution of
life. Could we learn something about how life
comes To be, how the building blocks for life
formed By looking at these complex organic carbon
reactions that Occur in the atmosphere on the surface of
Titan. So we can think of Titan as a Laboratory for understanding complex,
organic carbon chemistry that might Tell us something about how life
originates, and how The building blocks for life originate, in
planetary environments. So it's a very, very fascinating
environment, for astrobiologists. And quite apart from that, we can also
learn something About the incredible geology of a moon,
where mountains are carved By liquid methane, not liquid water, but
liquid methane. What do rivers of liquid methane do to
landscapes, and how do they form This unusual network of mountains and
valleys That we observe on the surface of Titan. One day we might even send probes to land
in these lakes and rivers, and follow the Flow of these rivers and, and map out the
movement of methane across these moons. And take photographs Of these incredible liquid methane
environments. But quite apart from the surface of Titan,
it also turns out That this is a very interesting moon in
its sub surface as well. This is cross section through the moon,
and it gives you some idea of what
We think is going on beneath that
fascinating Surface where all that organic chemistry
is occurring. And let's just look at those layers from
the outside in. So we have this organic rich Atmosphere in the surface we've just
talked about That atmosphere that gives it that brown
organic haze. And then, just beneath that, we've got an
ice layer, a liquid, a solid water ice Layer in clathrate, which is a sort of Cased ice material just beneath the
surface of Titan. And then beneath that, there may be a Liquid water ocean, a bit like Europa, and
Ganymede. But this Liquid water ocean may also contain
ammonia. We might be looking here at an ocean That's actually a mixture of liquid water
and ammonia. And then just beneath that, a layer of
high press, pressure ice. Unusual ice is at very high pressures that
form unique crystalline Structures, possibly ice six, and other
types of unusual icy structures. And then beneath that, a rocky core Much like other moons. A classical rocky core made up of
silicate. So, what we've got here is a very, very
unusual moon With a classic rocky core, but above that
strange layers of ice. Perhaps sub surface water, oceans, water
ammonia oceans. And then on the surface of that, an
unusual organic Chemistry that we can see directly with
our space programs. Why is this of interest To astrobiologists? Well, I've mentioned the interest in The surface environment for understanding
organic chemistry. We might ask questions like, if there is a
subsurface water-ammonia ocean In, in the subsurface of Titan, could it
be a location for life? Could it be a place where life originated? Could we even get samples of that ocean?
That would be a very difficult thing to
do. But we could start to ask questions about
habitable environments in the Sub surface of that moon. So for a whole range of angles, Titan is
of interest to astrobiologists. As we go from the surface, we've got
organic chemistry that might tell us Something about the origin of life, and Where the building blocks of life come
from. As we go to the subsurface, we have a
liquid water, Ammonia ocean, that might tell us about
possible habitable environments for life. May even be a location to look for life
today. And beneath that, the rocky cores, of
these icy Moons, tell us something about how these
moons formed. And how they may have led to habitable
conditions. So very briefly, that's a snapshot of some Of the other environments in the solar
system where We might learn something about the origin
of Life and also even look for habitable
environments today. It just shows you that you should make no
assumptions about Where habitable environments might be.
Some apparently very hostile places from Titan, to Triton and Ganymede can have
surprises beneath their surfaces. Liquid water that might be places for
habitable conditions. So what have we learned in this lecture? Well, we've learned that there are a
number of Possibilities for life in icy bodies in
the solar system. We've looked in this lecture course at Europa and Enceladus. In this lecture we see that there are a
multitude of other Planetary bodies, that could be places Where we could carry out astrobiological
investigations. We've also learned that much of the Speculation revolves around the idea of
liquid water. And we saw how earlier on in this lecture
course Liquid water is essential for life as we
know it. So that is the
Essential ingredient in all of this
discussion speculation. Any moon where there's liquid water could
be A place where we might hypothesize
habitats for life. Certainly might be places worth
investigating as places for life. Even if it's not there, we'll learn
something About conditions for habitable locations
elsewhere in the universe. And we've also learned that there are
places where we can learn about unusual Parts of astrobiology like the origin of
life, the Surface of Titan organic chemistry, and
complex organic chemistry. So in that brief collection of unusual
moons, we can see how there is a vast Range of information for astrobiologists
to go out and explore in the coming years.
