Brian Cox's Favourite Wonder - Wonders of the Solar System - BBC Two

I think that of all the wonders we chose,
my favourite became the one that

I thought might be the least interesting
at the start of the series.

But of all the worlds out there, this one,
Saturn's moon Titan is unique

because of that, that is an atmosphere

Titan has the most Earth like atmosphere
in the entire Solar System

a thick blue line rich in nitrogen and
containing methane.

It's minus 180 Celsius so in a sense it's
like a primordial Earth in deep freeze

you'd think nothing much was happening but
when we landed on it with the Huygens probe

a few years ago we found this intriguing
world

and we filmed in Alaska to look to talk
about the similarities between Titan and

Earth and you could imagine, you could just
sit there and in your mind's eye imagine

being stood on the surface of Titan

This is the Matanuska glacier in Alaska

It really is one of the most astonishing
places I have ever seen.

And this whole landscape is testament to
the erosive power of this stuff,

this mixture of ice and rock as it rolls
down this valley over hundreds of thousands

of years and creates this astonishing
landscape.

But the reason it can do that is because
of the delicate balance of the

earth's atmosphere. Our planet is just at
the right temperature and pressure to allow

water to exist as solid, as liquid and as
gas, as vapour in the clouds and so the

sun can heat up the oceans and it can move
the water over the top of the mountains

it can fall as rain turn to ice, become a
glacier and then sweep down the valley

to sculpt this astonishing landscape.

Just as our atmosphere allows all this to
exist, the atmosphere of Titan is the

perfect temperature and pressure to allow
something to exist that has never

been seen before on a world beyond Earth.

This is a picture taken of the South Pole
of Titan by Cassini in June 2005

and it's subsequently become one of the
most important and fascinating pictures in

the history of space exploration. The
interesting thing is this black blob here.

Now this fascinated the Cassini scientists
but the explanation as to what that is

had to wait just over a year to July 2006
when this picture was taken and it's a

radar image this time of the North Pole of
Titan and you see again these huge black areas.

Black in this case means that the radar
waves that bounced on to them didn't

come back so they're completely black and
there's only one really good explanation

for that, that is they're incredibly flat
surfaces, in fact they're surfaces of liquid

so this picture combined with this picture
means that this is the first observation

of a liquid, a lake on the surface of a
body other than the Earth in the Solar System.

But these lakes of course cannot be lakes
of liquid water because the

surface temperature on Titan is minus 180
degrees Celsius and at those temperatures

water is frozen as hard as steel.

So if these are not lakes of water
then what are they?