The Moon Page #4

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are still using that data.

So we're still operating,

in spite of the fact

that everybody's forgotten

what the word Apollo used to mean.

Each clear night, Wiant focuses

his telescope on the lunar surface

and fires a powerful laser

straight at the moon.

This will measure the exact

position of the moon in space.

All right,

we're ready to fire the laser.

What we hope is that our beam goes

from here to the moon surface

and it comes back and our goal

is to measure how long does it take

for our light to go from here

to the moon and back.

Their target is a simple device

placed on the moon

over 35 years ago.

The Apollo astronauts left behind

some simple glass reflectors,

rather like the reflectors

on a bicycle light.

This is a chunk of glass

that's a corner reflector.

And you can see it. It's three sides

and this would be the front side.

So light entering here

will go directly back to its source,

and then, our telescope

gathers that light

and then feeds it

to our detector.

There are four panels

of reflectors on the moon,

placed at four different sites.

This one I'm holding

in my hand is one.

And you can see

there's a row of ten by ten.

This a panel of a hundred of these

individual corner reflectors.

Look at the footprint.

You can see the astronaut's

footprint in the moon's surface here.

This is an Apollo 14 site,

the second site.

And, I don't know if you can see it,

but there's a... there's a bag...

there's a Ziploc bag right here.

You can see the red seam.

The astronauts were not required

to pick up their litter.

So there's a free Ziploc bag

if anybody would like to have it(!)

If the moon's orbit was fixed,

then its distance from the Earth

should have stayed the same

ever since Jerry

began his measurements.

But it hasn't.

The moon, it seems, is on the move.

The moon is receding

at a certain rate per year.

3.8cms per year, I believe,

that it's moving out,

moving away, receding.

It doesn't sound like much.

But over time, it's going to bring

some big changes.

As the moon pulls away, it'll put an end to

one of nature's most glorious spectacles -

a total solar eclipse.

The moon is 400 times smaller

than the sun.

But at the moment, it's also precisely 400

times closer to the Earth than the sun is.

This amazing coincidence means that, when the

moon passes directly in front of the sun,

it appears exactly the same size.

We are living at the only time

in the history of the solar system

when this unique spectacle

is possible.

As the moon drifts away from us,

this awe-inspiring sight

will be over forever.

So, over the years, scientists continued

to make new discoveries about our moon.

But somehow, it was never enough

to reignite our passion

for our closest neighbour.

And that was partly because

our attention had turned elsewhere.

There are over 150 other moons

in the solar system,

and, by the late 1970s,

we were starting to explore them.

The results were spectacular.

The journey of discovery began

with the Voyager probes.

They were sent to explore

the outer solar system -

the gas giants

like Jupiter and Saturn.

Until now,

these extraordinary worlds

had been seen only

through telescopes.

It took two years for these probes to

reach their first port of call - Jupiter.

Scientists all over the world

were gripped,

waiting for the first close-up

pictures of the great giant.

But when Voyager started

transmitting pictures back to Earth,

they were in for a surprise.

It seemed it was Jupiter's moons,

rather than the planet itself,

that held the most exciting secrets.

We thought the moons would be lumps

of ice covered in craters.

And that was about it.

But when Voyager started transmitting back

pictures of Jupiter's innermost moon, lo,

there was a strange anomaly.

A young NASA scientist spotted an

odd-looking bulge on the moon's side.

I came in about nine o'clock

that morning to the navigation area

and the pictures the spacecraft had

taken a day before were on my desk.

I put them on the computer system

and I displayed them,

and I could see that lo,

the moon of lo, was a crescent,

as very often our own moon

is a crescent in the night sky.

And I went

and enhanced the brightness,

and there appeared beside lo

an object -

a huge object that looked like

something I couldn't recognise

and could never have expected

and it completely captured

my attention.

I wanted to know so badly

what that was

that I had to ask myself,

"My goodness! What is that?!"

And the answer

that occurred to me first

was it looked like another moon,

peeking out behind lo.

But when she looked closer, she realised

it was something completely different.

When I explored it,

I was able to find

that this large, strange object

was this huge plume

of a volcanic eruption

arising 270km over the surface of

Io and raining back down onto it.

So I had discovered the first

ever volcanic eruption

ever seen on another world

besides the Earth.

Io's vibrant volcanic activity

is caused by the

massive gravitational pull

exerted by Jupiter, which squeezes

and heats the moon internally.

You could actually see,

looking at the edge of lo,

plumes of what turned out to be

sulphur dioxide gas

shooting up into space,

about 100 miles,

and dropping all this sulphur

dioxide snow back onto the surface,

and the whole place is stained

red and yellow with sulphur.

It's an incredible place.

Here was a moon to swoon over.

It was far more exciting and exotic

than our own boring, lifeless moon.

And lo was just the beginning.

Soon, another of Jupiter's moons -

Europa - was also wowing scientists.

Europa's surface had no craters.

Close up, it was covered

in cracks and canyons.

Europa clearly had

a very young surface.

We could tell that there weren't

many large impact craters

and the surface

was relatively smooth and cracked.

Not chasms going deep down into it,

but cracks filled

with something darker.

A recently active surface.

Looking at it, scientists realised

it was similar

to scenes they knew from Earth,

from the poles.

Europa was covered in ice.

And because there were no craters,

they knew that the ice must have

melted and refrozen many times.

And that could mean

only one thing -

there had to be liquid water,

the crucial ingredient

for life on Europa.

It got even more exciting

when scientists began to speculate

where the heat to melt the ice

was coming from.

Again, the answer

lay within our own planet.

On the floors

of the oceans of the Earth,

scientists had discovered

"black smokers" -

volcanic heat sources coming

from below the Earth's crust,

warming the water from below.

Perhaps hot vents like these could

exist under Europa's icy crust.

Scientists could barely contain

their excitement.

Liquid water

and a volcanic heat source

sounded like the kind of conditions

that many believe

gave birth to life on Earth.

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