Other Icy Bodies

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En provenance du cours de The University of Edinburgh

Astrobiology and the Search for Extraterrestrial Life

1156 notes

The University of Edinburgh

Astrobiology and the Search for Extraterrestrial Life

1156 notes

Learn about the origin and evolution of life and the search for life beyond the Earth.

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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?

Other Icy Bodies14:42

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Charles Cockell
Professor
Astrobiology

[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.

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