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Lift off of Messenger on NASA'S
mission to Mercury.
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[The Void by Muse]
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♪ They'll say no-one can see us
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♪ That we're estranged and all alone
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♪ They believe nothing can reach us
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♪ And pull us out of
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♪ The boundless gloom
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♪ They're wrong
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♪ They're wrong
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♪ They're wrong. ♪
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Our planetary neighbour, Mars,
is a cold, barren rock.
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Its rusted surface
covered in parched sand.
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But, beneath the dust,
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the planet bears the scars
of a former life.
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Billions of years ago,
Mars was just like Earth.
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A world with a thick atmosphere
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that supported oceans of water.
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But, today, that world is gone.
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Mars lies dead,
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while the Earth thrives.
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Why the two planets had such
different fates is a mystery
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that we've only just begun
to answer.
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You see that pale red point
of light in the sky,
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just there?
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That's Mars.
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Through a small telescope,
it appears almost Earth-like.
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Our sister world -
polar ice caps and dark surface
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markings that 19th-century
astronomers thought were vegetation,
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even canals bringing
meltwater down from the poles
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to arid equatorial cities.
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Across the depths of space,
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the inhabitants watched us "with
envious eyes", wrote HG Wells.
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We now know that there are no
eyes looking back at us.
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Mars is a frozen, arid desert world.
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But a fleet of spacecraft
have revealed
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that it hasn't always been that way.
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Mariner 4 was successfully
launched on time
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for its historic 228-day
journey to Mars.
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Picture information started
to come in on July 15th, 1965.
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A revelation comparable to
Galileo's first view
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of the moon through a telescope.
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During its brief flyby,
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Mariner 4 gave us our first
close-up glimpses of Mars.
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When Mariner 9 was placed
into an orbit around Mars,
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it saw a planet blanketed
by a gigantic dust storm.
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In nearly a year of operation,
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they transmit more than 7,000
photographs.
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From orbit, Mariner 9 photographed
80% of the Martian surface.
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First of all, there are two eyes,
not only in colour but also
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in stereo, and in the infrared
part of the spectrum.
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It has a sense of touch,
it has a sense of hearing,
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but by far the most important
feature of the lander is its brain.
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The Viking programme took
us down to the ground
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for the first time...
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Touchdown, we have touched down.
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..and revealed Mars...
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Perfect set-down.
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..like never before.
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There is the first piece
of information coming in.
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Oh! Oh!
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The data gathered over the last 50
years has allowed us to create
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detailed maps of the Martian
surface...
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..and begin to piece
together its past.
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Maps of Mars are like storybooks.
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You can read the history
of the planet
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written across its surface, and the
reason for that is that there's
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virtually no erosion,
hasn't been for billions of years,
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so the scars of events that
happened even four billion years ago
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can still be seen.
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This is a type of map
called an elevation map.
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The colours correspond to difference
in heights on the surface,
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so blue means low
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and red and whites are high.
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Now, this region here, which is much
higher on average than the rest
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of Mars, is called Tharsis
and it's covered in volcanoes,
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including the largest volcano
in the solar system, Olympus Mons.
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At the other side of Tharsis
is the great Valles Marineris,
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the Mariner Valley,
and it is a canyon that dwarfs
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anything we see on Earth.
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On the opposite side of the planet
is an impact basin called Hellas.
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The height difference from
the crater rim
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to the crater floor is 9km.
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That means you could fit Everest
in the middle of there
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and look down on its summit.
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And the region surrounding the
basin reveals Mars' former life.
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The Hellas basin is punched into the
oldest-surviving terrain on Mars.
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It's called Noachis Terra
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or The Land Of Noah.
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And that's a wonderfully evocative
name because its surface is sculpted
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by flowing water.
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All across the earliest Martian
surface, we've glimpsed traces
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of what appear to have
been lakes and rivers.
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And so a new generation
of spacecraft has been sent to Mars,
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to investigate the existence
of water...
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..and what happened to the planet
for it all to disappear.
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Led by the most audacious Mars
mission ever attempted...
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We have two-way Doppler and orbit
around the planet Mars.
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..to land a one-tonne rover
on the Martian surface.
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Its final descent has become known
as the "seven minutes of terror".
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Curiosity touched down in
Gale crater,
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a 150-kilometre-wide impact basin,
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thought to have been home
to an ancient lake.
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The rover is a 2.5 billion
mobile chemistry lab...
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..designed to take samples
of the Martian surface
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and analyse its composition.
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As it explored the crater,
Curiosity saw pebbles polished
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and rounded by running water
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in what had once been rivers
and streams.
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Then, 61 days after landing,
Curiosity identified the perfect
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spot to begin its primary mission.
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In a sandy area of the crater
called the Rocknest,
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the rover took its first
scoops of Martian soil.
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Chemical analysis of the fine,
dusty sand revealed
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something quite unexpected.
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Even though the surface of Mars
appears completely dry,
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2% of the soil is still
made up of water.
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Curiosity had found evidence
of just how wet a planet
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ancient Mars had been.
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For hundreds of millions of years,
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Mars was a water world.
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Rains fell,
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rivers ran,
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and, in the northern hemisphere,
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water collected in a vast sea
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that covered a fifth
of the Martian surface.
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The Red Planet was once blue.
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All the evidence suggests
that there were large bodies
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of standing water on Mars
around 4 billion years ago,
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and the atmospheric pressure
was at least that of Earth today,
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perhaps even higher.
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Temperatures were around 25 degrees,
so I could have sat on Mars
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all those years ago,
admittedly with a mask to breathe,
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because there was very little
oxygen, but I could have sat there
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and looked out over a view
like that.
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So, you don't have to imagine
what Mars was like in the past.
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You can experience it.
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It was pretty much like this.
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But, within a billion years,
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all Mars' lakes and seas
had disappeared.
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In our solar system,
only one blue planet survives...
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..Mars' sister, Earth.
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70% of our planet's surface
is covered by ocean.
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Under the waves,
a million species thrive.
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While on land, the rains support
Earth's delicate ecosystems...
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..providing a home for
an abundance of life.
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But it hasn't always been this way.
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The early Earth was unrecognisable
from the planet we know today.
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Its atmosphere thick
with carbon dioxide.
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And its oceans acidic.
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Four billions years ago,
Earth was a troubled, toxic world...
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..while Mars was flourishing.
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But both planets were
about to be engulfed
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by a cataclysm from space.
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To understand what happened,
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we have to look beyond
our own world.
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You can't read the deep history
of the Earth by looking
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at its surface because our planet
is a geologically active world.
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The surface is constantly
being reshaped by volcanic activity,
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weathering, and the actions of
the oceans, but we have a companion,
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the moon, which has been inactive
for many billions of years,
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and so the history of events
that happened in this region
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of the solar system is written
all over its surface.
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The most distinctive feature
of the moon's surface
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are its craters - it is literally
covered in a record of impacts
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from space, and that allows us
to estimate the relative ages
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of different parts of the moon.
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Quite simply, if there
are more craters,
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then that piece
of the moon must be older.
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There's been more time
for the impacts to build up.
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But we can do better
than just measure the relative ages
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because we have rocks,
the moon rocks brought back
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by the Apollo astronauts.
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We can estimate the ages of rocks
very precisely by looking
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at the rates of decay of radioactive
elements inside them.
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They're like little stopwatches
that start ticking the moment
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the rocks are formed, in this case
by the impacts from space.
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So, the moon rocks allow us
to tie the number of craters
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in a particular region of the moon
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to an absolute age measured
by the rocks.
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And this doesn't just allow us to
date impacts on the lunar surface.
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It means that craters can be used
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to read the histories of worlds
across the solar system.
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Including Mars.
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When we gathered all the data,
we discovered something surprising.
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There was a peak in the crater
formation rate, about 3.8
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to 3.9 billion years ago,
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which signified a period of intense
violence in the solar system,
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and that is called the
Late Heavy Bombardment.
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Countless asteroids fragmented
in Mars' atmosphere,
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raining havoc across the planet.
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It's estimated that
53 tonnes of rock
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fell on every square
metre of Mars.
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Over a third of the planet's
surface was obliterated...
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..and Mars was pushed
to the brink of death.
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Whilst the evidence from the
surface of the moon tells us
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that the Late Heavy Bombardment
happened, it doesn't tell us why.
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For that, we have to resort
to computer models of the evolution
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of the solar system,
and, when we do that,
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they point the finger at Neptune.
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It's thought that Neptune migrated
outwards into the Kuiper belt...
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..a region of icy, rocky objects
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orbiting at the edge
of the solar system.
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The resulting gravitational
interactions disrupted those orbits
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and sent many of the objects inwards
to the inner solar system,
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and that may have been the cause
of the Late Heavy Bombardment.
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Earth also suffered the onslaught,
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and, for tens of millions of years,
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the fortunes of the two sister
worlds hung in the balance.
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But, just when conditions appeared
at their least promising,
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Earth's most precious
characteristic emerged.
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Life.
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There is good evidence that life
was present on Earth
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around 3.8 billion years ago,
and discounting the - I think -
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remote possibility
that life began elsewhere
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00:23:08,540 --> 00:23:11,140
in the solar system
and was transported to the Earth
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00:23:11,140 --> 00:23:13,260
on meteorites or comets,
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00:23:13,260 --> 00:23:16,740
that means that life must
have begun here.
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00:23:16,740 --> 00:23:19,900
So, somewhere on this planet
there was a transition
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00:23:19,900 --> 00:23:23,340
from geochemistry -
the chemistry of Earth,
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00:23:23,340 --> 00:23:26,300
to biochemistry -
the chemistry of life.
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00:23:42,340 --> 00:23:46,220
And whilst the precise details
of how that transition occurred
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00:23:46,220 --> 00:23:52,020
remain a mystery, it's thought
that in warm volcanic pools
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00:23:52,020 --> 00:23:56,380
or deep sea hydrothermal vents,
conditions were right
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for the chemical building blocks
of life to form spontaneously.
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00:24:05,860 --> 00:24:08,580
And that means that
if similar conditions
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00:24:08,580 --> 00:24:11,300
were to be found elsewhere
in the solar system,
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00:24:11,300 --> 00:24:14,900
it might be possible
that life began there too.
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00:24:20,580 --> 00:24:26,220
Ignition, and lift off of
the Atlas V rocket with MRO.
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Surveying for the deepest
insights
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00:24:29,940 --> 00:24:32,140
into the mysterious
evolution of Mars.
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00:24:34,780 --> 00:24:39,340
So, in 2005, NASA embarked
on a mission to look
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for those same environments on Mars.
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00:24:57,540 --> 00:25:01,060
For more than a decade,
the Mars Reconnaissance Orbiter
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00:25:01,060 --> 00:25:03,860
has been our eyes on the
Red Planet...
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00:25:09,460 --> 00:25:11,860
..sending back more data
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00:25:11,860 --> 00:25:14,900
than all the other Mars
missions combined.
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00:25:21,060 --> 00:25:25,860
MRO has made more than
60,000 orbits,
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00:25:25,860 --> 00:25:29,820
mapping over 99%
of the planet's surface.
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00:25:35,860 --> 00:25:41,540
Its high-resolution cameras
have revealed Mars as never before,
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discovering polar avalanches,
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00:25:46,460 --> 00:25:48,620
shifting sand dunes...
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00:25:52,500 --> 00:25:58,540
..and what could be seasonal flows
of sand or even liquid meltwater.
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Then, in 2017, MRO turned its gaze
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to one of the Red Planet's
oldest features,
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00:26:12,020 --> 00:26:13,980
the Eridania Basin.
246
00:26:18,380 --> 00:26:23,260
3.8 billion years ago,
the basin was a vast sea...
247
00:26:26,700 --> 00:26:28,820
..holding ten times more water
248
00:26:28,820 --> 00:26:31,820
than the Great Lakes of
North America.
249
00:26:37,260 --> 00:26:41,420
And it was here that MRO found
the evidence it was looking for.
250
00:26:43,940 --> 00:26:49,740
400-metre-thick deposits
of minerals that, on Earth,
251
00:26:49,740 --> 00:26:53,100
form in deep sea hydrothermal vents.
252
00:27:00,500 --> 00:27:05,580
In the Eridania Basin,
MRO revealed that conditions on Mars
253
00:27:05,580 --> 00:27:08,860
had once been ripe
for the emergence of life.
254
00:27:33,140 --> 00:27:37,660
We won't know for sure whether life
began or even perhaps still exists
255
00:27:37,660 --> 00:27:41,340
on Mars until we go there
and find physical evidence -
256
00:27:41,340 --> 00:27:45,740
so, microbes buried deep below the
soil in oases of liquid water,
257
00:27:45,740 --> 00:27:49,420
or maybe microbe fossils -
but what we do know is that,
258
00:27:49,420 --> 00:27:53,220
when life began here on Earth,
3.8 billion years ago,
259
00:27:53,220 --> 00:27:55,580
the conditions on Mars
were very similar.
260
00:27:55,580 --> 00:27:58,100
There were seas,
there was volcanic activity,
261
00:27:58,100 --> 00:28:02,220
there were even hydrothermal vent
systems on the floors of its oceans.
262
00:28:02,220 --> 00:28:05,860
So, it is at least possible
that Earth is not the only world
263
00:28:05,860 --> 00:28:08,540
in the solar system
where life began.
264
00:28:15,220 --> 00:28:17,940
The habitable conditions
during what's known
265
00:28:17,940 --> 00:28:23,140
as Mars' Noachian era persisted
for hundreds of millions of years.
266
00:28:32,340 --> 00:28:37,340
But then, prospects for life on
the Red Planet changed dramatically.
267
00:28:43,580 --> 00:28:47,860
Around 3.5 billion years ago,
the Noachian era drew to a close
268
00:28:47,860 --> 00:28:52,740
and Mars entered a more frozen,
arid phase, known as the Hesperian.
269
00:28:52,740 --> 00:28:56,820
The water that flowed freely over
the surface during the age of Noah
270
00:28:56,820 --> 00:29:01,300
became locked away
in giant reservoirs of ice.
271
00:29:01,300 --> 00:29:05,580
But, around the same time, Mars
became more volcanically active,
272
00:29:05,580 --> 00:29:08,620
and the volcanic eruptions
and sub-surface lava flows
273
00:29:08,620 --> 00:29:13,220
occasionally melted the ice,
leading to catastrophic flooding.
274
00:29:13,220 --> 00:29:16,260
They must have been some of
the most spectacular sights
275
00:29:16,260 --> 00:29:18,540
in the history of the solar system.
276
00:29:25,620 --> 00:29:29,660
As molten rock pushed
upwards through the crust,
277
00:29:29,660 --> 00:29:32,900
meltwater poured out
onto the surface.
278
00:29:36,900 --> 00:29:39,460
It raged down from
the southern highlands...
279
00:29:44,060 --> 00:29:49,500
..until, in a place known
as Echus Casma, it plunged
280
00:29:49,500 --> 00:29:52,060
over cliffs 4km high...
281
00:30:02,180 --> 00:30:05,380
..creating the largest waterfall
282
00:30:05,380 --> 00:30:08,260
the solar system has ever seen.
283
00:30:49,020 --> 00:30:53,260
Echus Casma would have been like
no waterfall ever seen on Earth.
284
00:30:53,260 --> 00:30:57,820
350 cubic kilometres
of water flowed over it.
285
00:30:57,820 --> 00:31:02,660
That's like a cube 70km by 70km
by 70km.
286
00:31:02,660 --> 00:31:06,020
It all entered into a canyon
10km wide
287
00:31:06,020 --> 00:31:10,980
and 100km long,
and that happened in a few weeks.
288
00:31:19,500 --> 00:31:22,820
Once the flood subsided,
the water disappeared...
289
00:31:25,820 --> 00:31:30,180
..leaving the evidence of the falls
etched into the face of the planet.
290
00:31:38,860 --> 00:31:42,700
We don't know precisely why
the climate of Mars changed
291
00:31:42,700 --> 00:31:45,460
from warm and wet
to cold and arid.
292
00:31:45,460 --> 00:31:47,860
We're talking about events
that happened
293
00:31:47,860 --> 00:31:51,340
three and a half billion years ago
on a planet hundreds of millions
294
00:31:51,340 --> 00:31:55,460
of kilometres away,
so it is a hard problem.
295
00:31:55,460 --> 00:31:58,700
But we do strongly suspect
that changes happening
296
00:31:58,700 --> 00:32:00,980
on the planet's surface were driven
297
00:32:00,980 --> 00:32:04,260
at least in part by changes
in the planet's interior.
298
00:32:11,500 --> 00:32:13,660
Deep within Mars' core,
299
00:32:13,660 --> 00:32:16,980
something was causing
the planet to die...
300
00:32:18,420 --> 00:32:23,340
..and the evidence can be found
in Mars' atmosphere.
301
00:32:23,340 --> 00:32:28,420
T-minus ten, nine,
eight, seven, six,
302
00:32:28,420 --> 00:32:30,860
five, four, three,
303
00:32:30,860 --> 00:32:32,740
two, one.
304
00:32:32,740 --> 00:32:36,700
Main engine start,
ignition, and lift-off
305
00:32:36,700 --> 00:32:39,340
of the Atlas V with MAVEN,
306
00:32:39,340 --> 00:32:42,180
looking for clues about
the evolution of Mars
307
00:32:42,180 --> 00:32:43,860
through its atmosphere.
308
00:32:49,420 --> 00:32:53,540
In September 2014,
NASA'S MAVEN probe made its final
309
00:32:53,540 --> 00:32:55,820
approach to the Red Planet.
310
00:33:10,540 --> 00:33:14,420
Its mission - to understand
what drove the planet's
311
00:33:14,420 --> 00:33:16,140
dramatic climate change.
312
00:33:28,620 --> 00:33:32,420
MAVEN is equipped with an array
of instruments designed to measure
313
00:33:32,420 --> 00:33:36,780
the behaviour of the atoms
and molecules in Mars' atmosphere.
314
00:34:28,460 --> 00:34:32,060
The spacecraft circles Mars
in an elliptical orbit...
315
00:34:41,060 --> 00:34:43,340
..allowing it to measure the
full profile
316
00:34:43,340 --> 00:34:45,620
of the planet's upper atmosphere.
317
00:34:54,020 --> 00:34:55,580
At its lowest point,
318
00:34:55,580 --> 00:34:58,980
it's just 150km above the surface.
319
00:35:02,020 --> 00:35:05,340
At its highest, a little
over 6,000 kilometres.
320
00:35:09,620 --> 00:35:13,900
And it was at the very top of
Mars' atmosphere that MAVEN found
321
00:35:13,900 --> 00:35:17,340
the key to the mystery
of what happened to Mars.
322
00:35:23,380 --> 00:35:26,980
Detailed measurements
revealed gas is being lost
323
00:35:26,980 --> 00:35:29,260
from the Martian atmosphere,
324
00:35:29,260 --> 00:35:31,700
escaping to space
325
00:35:31,700 --> 00:35:35,100
at a rate of about two kilograms
every second.
326
00:35:39,980 --> 00:35:45,500
Over time, it's thought this gradual
stripping away of Mars' atmosphere
327
00:35:45,500 --> 00:35:50,140
has slowly thinned the insulating
layer surrounding the planet...
328
00:35:52,940 --> 00:35:55,900
..causing surface
temperatures to plummet.
329
00:36:14,100 --> 00:36:18,300
But what was it that caused Mars
to lose its atmosphere
330
00:36:18,300 --> 00:36:20,980
while Earth clung on to hers?
331
00:36:29,540 --> 00:36:33,860
150 million kilometres away in that
direction is the setting sun,
332
00:36:33,860 --> 00:36:36,740
a giant nuclear fusion reactor.
333
00:36:36,740 --> 00:36:38,900
You can fit one million
Earths inside it.
334
00:36:38,900 --> 00:36:40,940
Now, the surface temperature
335
00:36:40,940 --> 00:36:43,540
is only around 6,000 degrees
Celsius,
336
00:36:43,540 --> 00:36:46,020
but the sun's atmosphere,
known as its corona,
337
00:36:46,020 --> 00:36:47,620
is at one million degrees.
338
00:36:47,620 --> 00:36:50,860
And that means it's in the form
of what's known as a plasma, a soup
339
00:36:50,860 --> 00:36:53,100
of electrically charged particles.
340
00:36:53,100 --> 00:36:56,940
Some of those particles are moving
around so fast that they can escape,
341
00:36:56,940 --> 00:37:00,180
and they stream away in what's
known as the solar wind.
342
00:37:00,180 --> 00:37:03,980
They reach the Earth travelling at
a few hundred kilometres per second.
343
00:37:03,980 --> 00:37:07,420
And, if we weren't protected, they
would strip away our atmosphere.
344
00:37:17,380 --> 00:37:20,220
And when the sun dips
below the horizon...
345
00:37:22,660 --> 00:37:27,500
..there are times when that
protective force field is revealed.
346
00:37:46,740 --> 00:37:48,740
Just look at that!
347
00:37:48,740 --> 00:37:51,060
I mean, there is the aurora.
348
00:37:55,340 --> 00:37:59,020
It's the laws of nature,
all of them, written across the sky.
349
00:38:02,900 --> 00:38:06,500
Electrically-charged particles
have been driven away from the sun,
350
00:38:06,500 --> 00:38:11,380
ultimately from nuclear fusion
reactions in the core of a star.
351
00:38:11,380 --> 00:38:15,380
They're crossing the solar system,
hitting the Earth's magnetic field,
352
00:38:15,380 --> 00:38:19,180
stretching it out
on the dark side of the planet.
353
00:38:19,180 --> 00:38:22,980
The field then snaps back
like an elastic band,
354
00:38:22,980 --> 00:38:26,900
accelerating all of those charged
particles up and down
355
00:38:26,900 --> 00:38:30,260
the field lines to the poles,
which is here in the skies
356
00:38:30,260 --> 00:38:33,980
over Iceland, and they hit nitrogen
357
00:38:33,980 --> 00:38:37,020
and oxygen molecules
in the atmosphere.
358
00:38:38,540 --> 00:38:42,460
And you're seeing quantum
mechanics - they're exciting the
359
00:38:42,460 --> 00:38:45,380
molecules so that they emit light
in characteristic colours.
360
00:38:58,020 --> 00:39:00,540
And, if you think about it,
this is the only time
361
00:39:00,540 --> 00:39:03,860
that we really see
the Earth's magnetic field.
362
00:39:05,220 --> 00:39:08,180
It's one of the reasons why life
on Earth
363
00:39:08,180 --> 00:39:11,340
has been able to
persist for four billion years.
364
00:39:14,220 --> 00:39:17,460
In a sense, that's
the reason that you exist.
365
00:39:22,700 --> 00:39:26,340
It's Earth's magnetic field
that protects our atmosphere
366
00:39:26,340 --> 00:39:29,380
from the ravages of the solar wind,
367
00:39:29,380 --> 00:39:32,620
and that protective shield
has its origins deep
368
00:39:32,620 --> 00:39:34,420
in the planet's interior.
369
00:39:36,620 --> 00:39:40,020
Thousands of kilometres
down below my feet,
370
00:39:40,020 --> 00:39:43,580
actually below your feet now,
is the Earth's outer core,
371
00:39:43,580 --> 00:39:46,860
which is a seething
mass of molten iron.
372
00:39:46,860 --> 00:39:50,860
Convection currents cause
the molten iron to rise,
373
00:39:50,860 --> 00:39:54,860
and then the Earth's
rotation causes it to spiral around.
374
00:39:54,860 --> 00:39:57,340
Now, a spiralling, circling flow
375
00:39:57,340 --> 00:40:01,100
of an electrically conducting
liquid is a dynamo.
376
00:40:01,100 --> 00:40:05,860
A dynamo generates a magnetic field
and the Earth's field rises up,
377
00:40:05,860 --> 00:40:09,500
not just to the surface here,
but out into space,
378
00:40:09,500 --> 00:40:11,540
forming our protective shield.
379
00:40:11,540 --> 00:40:14,420
And that is what you see there.
380
00:40:21,420 --> 00:40:23,620
And just like Earth,
381
00:40:23,620 --> 00:40:27,220
ancient Mars was also shielded
from the sun.
382
00:40:33,620 --> 00:40:36,460
Aurora once danced above
its poles...
383
00:40:39,620 --> 00:40:44,620
..keeping guard over the Martian
atmosphere and seas below.
384
00:41:00,340 --> 00:41:04,020
But between 3.5 and 4 billion
years ago,
385
00:41:04,020 --> 00:41:06,620
Mars' dynamo switched off.
386
00:41:09,580 --> 00:41:13,620
The aurora surrounding the poles
slowly faded away
387
00:41:13,620 --> 00:41:15,740
as the magnetic field diminished...
388
00:41:18,340 --> 00:41:21,300
..allowing the atmosphere
to be stripped away
389
00:41:21,300 --> 00:41:22,940
by the solar wind.
390
00:41:32,740 --> 00:41:38,140
Without protection,
seas evaporated, the surface froze,
391
00:41:38,140 --> 00:41:41,620
and Mars was transformed.
392
00:41:50,100 --> 00:41:54,060
At the same time, the fortunes
of Mars' sister world
393
00:41:54,060 --> 00:41:56,500
were about to take
a very different turn.
394
00:42:00,900 --> 00:42:04,620
For the next billion years or so,
Earth was indistinguishable
395
00:42:04,620 --> 00:42:06,900
from those landscapes of early Mars-
396
00:42:06,900 --> 00:42:10,220
barren continents surrounded
by ocean.
397
00:42:10,220 --> 00:42:14,820
But in Earth's oceans, life was
beginning to transform the planet.
398
00:42:18,540 --> 00:42:22,780
Primitive algae started
to neutralise the ocean's acidity
399
00:42:22,780 --> 00:42:26,780
and replace the dense red fog
of Earth's methane-rich
400
00:42:26,780 --> 00:42:28,940
atmosphere with oxygen.
401
00:42:32,540 --> 00:42:37,060
Around 600 million years ago,
that oxygen-rich atmosphere allowed
402
00:42:37,060 --> 00:42:41,300
complex life to evolve
in the oceans, colonise the land,
403
00:42:41,300 --> 00:42:45,860
and ultimately produce this
almost-infinitely rich living world
404
00:42:45,860 --> 00:42:48,220
today, of which we are a part.
405
00:43:00,100 --> 00:43:04,060
While Mars died, Earth flourished.
406
00:43:10,380 --> 00:43:15,220
To understand why the two sisters
had such different destinies,
407
00:43:15,220 --> 00:43:17,780
you have to go right back
408
00:43:17,780 --> 00:43:21,300
to the time the planets
were forming.
409
00:43:26,220 --> 00:43:28,420
When Mars and Earth were born,
410
00:43:28,420 --> 00:43:32,540
the solar system was a chaotic
vortex of gas and rock.
411
00:43:37,220 --> 00:43:43,300
Material clumped together and grew,
only to be smashed apart.
412
00:43:51,540 --> 00:43:54,900
Over time, some of the objects
became large enough to survive
413
00:43:54,900 --> 00:43:58,260
at least the smaller impacts,
and continued to grow,
414
00:43:58,260 --> 00:44:01,740
including the embryonic
planets Earth and Mars.
415
00:44:10,500 --> 00:44:15,020
But there was one crucial difference
between the young planets.
416
00:44:21,620 --> 00:44:24,500
Mars formed in a region
of the solar system
417
00:44:24,500 --> 00:44:27,220
with considerably
less rocky material.
418
00:44:28,260 --> 00:44:31,500
And that had a profound impact
on the planet's growth.
419
00:44:37,060 --> 00:44:40,900
Mars is a significantly smaller
world - it's about half the diameter
420
00:44:40,900 --> 00:44:43,660
of the Earth, and that makes
all the difference.
421
00:44:43,660 --> 00:44:47,180
Although the details are not
yet fully understood,
422
00:44:47,180 --> 00:44:51,540
it seems clear that Mars' smaller
size meant that its dynamo switched
423
00:44:51,540 --> 00:44:53,900
off many billions of years ago.
424
00:44:57,540 --> 00:45:01,940
Being smaller meant Mars' core
cooled more quickly than Earth's.
425
00:45:04,700 --> 00:45:07,900
And this is certainly part
of the reason why Mars
426
00:45:07,900 --> 00:45:09,700
lost its magnetic field.
427
00:45:16,660 --> 00:45:20,100
Even though the planet is further
away from the sun than we are,
428
00:45:20,100 --> 00:45:23,220
that meant that the solar wind
stripped away its atmosphere
429
00:45:23,220 --> 00:45:25,180
and Mars died.
430
00:45:25,180 --> 00:45:30,380
So, even though Earth and Mars
are so similar in so many ways,
431
00:45:30,380 --> 00:45:34,340
the difference in position
and size in the solar system
432
00:45:34,340 --> 00:45:36,780
led to very different fates.
433
00:45:47,420 --> 00:45:51,180
Long ago, two sister
worlds were born.
434
00:45:55,860 --> 00:45:59,540
In childhood, Mars was warm
and wet...
435
00:46:05,020 --> 00:46:09,140
..whilst the Earth was
inhospitable and toxic.
436
00:46:17,260 --> 00:46:20,100
Both young planets survived
the violence
437
00:46:20,100 --> 00:46:24,580
of the Late Heavy Bombardment,
438
00:46:24,580 --> 00:46:28,660
emerging as mature worlds,
439
00:46:28,660 --> 00:46:32,580
primed with all the ingredients
for life.
440
00:46:42,020 --> 00:46:46,820
But deep inside, the smaller
of the two was dying.
441
00:46:53,300 --> 00:46:55,500
Mars' seas dried up.
442
00:47:07,540 --> 00:47:14,140
And as the planet's interior cooled,
one by one her fires went out.
443
00:47:18,980 --> 00:47:23,420
Olympus Mons, the largest volcano
in the solar system,
444
00:47:23,420 --> 00:47:26,860
last erupted around
25 million years ago.
445
00:47:35,940 --> 00:47:39,420
As the lava turned to stone,
446
00:47:39,420 --> 00:47:42,460
Mars was frozen in time.
447
00:47:56,980 --> 00:48:03,580
And so, today, her surface lies
rusted and gathering dust.
448
00:48:11,180 --> 00:48:14,660
But that might not be
the end of Mars' story.
449
00:48:22,620 --> 00:48:27,060
Because the next generation of
spacecraft are already on their way.
450
00:48:35,580 --> 00:48:39,900
NASA Orion - currently
in advanced testing.
451
00:49:10,180 --> 00:49:12,860
ESA ExoMars -
452
00:49:12,860 --> 00:49:17,260
a fleet of spacecraft designed
to search for signs of life.
453
00:49:27,380 --> 00:49:31,700
And the most ambitious private
space mission ever conceived.
454
00:49:42,740 --> 00:49:48,460
A launch vehicle developed to take
humans to the surface of Mars.
455
00:50:05,940 --> 00:50:08,900
Mars is, in a sense, a failed world,
456
00:50:08,900 --> 00:50:13,700
a faded ember etched with the
memories of a more enticing past,
457
00:50:13,700 --> 00:50:18,660
but there may have been,
and may still be, life on Mars.
458
00:50:18,660 --> 00:50:22,300
And the discovery of a second
genesis in our solar system
459
00:50:22,300 --> 00:50:26,940
would have profound philosophical,
scientific and cultural consequences
460
00:50:26,940 --> 00:50:30,100
because it would mean
there is a sense of inevitability
461
00:50:30,100 --> 00:50:31,940
about the origin of life,
462
00:50:31,940 --> 00:50:34,340
and that would mean that the
universe
463
00:50:34,340 --> 00:50:38,620
is most likely teeming with life -
that we are not alone.
464
00:50:44,140 --> 00:50:48,140
But equally importantly, I think,
is the role that a planet
465
00:50:48,140 --> 00:50:52,100
with a history like Mars
could play in our future.
466
00:50:52,100 --> 00:50:56,540
Mars is rich in resources,
it has vast reservoirs of frozen
467
00:50:56,540 --> 00:50:59,020
water below the surface,
and minerals -
468
00:50:59,020 --> 00:51:02,700
iron, nitrogen, carbon, oxygen -
all the things
469
00:51:02,700 --> 00:51:04,900
you need to support a civilisation.
470
00:51:07,060 --> 00:51:09,780
And that's why I think
that, in my lifetime,
471
00:51:09,780 --> 00:51:13,820
there will be Martians,
but the Martians will be us.
472
00:51:13,820 --> 00:51:16,980
We will go to Mars
and make it our home,
473
00:51:16,980 --> 00:51:20,460
and that old red world
will become our first step
474
00:51:20,460 --> 00:51:24,020
beyond the cradle, and out
to the stars.
475
00:51:56,220 --> 00:51:58,900
Mars really captures
476
00:51:58,900 --> 00:52:01,940
our imagination,
477
00:52:01,940 --> 00:52:05,020
partly because it's so close.
478
00:52:05,020 --> 00:52:09,700
I think people are really interested
in Mars because it actually
479
00:52:09,700 --> 00:52:11,940
is so similar to Earth.
480
00:52:11,940 --> 00:52:16,820
It's close by, it's easy to travel
there with robots
481
00:52:16,820 --> 00:52:21,060
and space missions, and so we've
done a lot of exploration.
482
00:52:21,060 --> 00:52:24,500
And, every time you go and look,
you discover something new.
483
00:52:28,420 --> 00:52:32,940
NASA Curiosity launched
on the 26th of November, 2011.
484
00:52:35,940 --> 00:52:38,580
But the biggest obstacle
facing the mission team
485
00:52:38,580 --> 00:52:40,220
wasn't leaving the Earth.
486
00:52:43,780 --> 00:52:45,460
Mars has a unique set of challenges
487
00:52:45,460 --> 00:52:48,060
compared to other places
we go with spacecraft.
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Mars has an atmosphere
but it's thin, so it's not enough
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00:52:51,860 --> 00:52:53,060
to really slow you down,
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00:52:53,060 --> 00:52:55,980
but it is enough to actually burn
you up as you're trying to land.
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00:52:58,580 --> 00:53:01,580
Curiosity reached the top
of the Martian atmosphere,
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00:53:01,580 --> 00:53:04,180
travelling at 20,000km per hour.
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00:53:07,060 --> 00:53:09,740
Curiosity is a big rover.
It weighs a metric ton,
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00:53:09,740 --> 00:53:12,260
and so landing that required
every trick in the book
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00:53:12,260 --> 00:53:14,780
of how we've learned to land
on Mars with previous missions.
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To land safely, the rover
had to be slowed
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to less than 4km per hour.
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00:53:31,180 --> 00:53:33,580
You end up arriving
at Mars going really fast,
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so you actually have to slow down,
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00:53:35,780 --> 00:53:38,540
and we do that using a heat shield,
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which burns off a lot of energy
and creates a lot of heat,
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00:53:41,940 --> 00:53:44,940
so you have to absorb that somehow
and not damage the spacecraft.
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Then a parachute comes out.
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00:53:51,140 --> 00:53:53,980
The biggest parachute we've ever
used in a planetary mission.
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00:53:56,260 --> 00:53:59,060
And that even doesn't slow
Curiosity down enough,
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because Mars' atmosphere is quite
thin, so then rockets carry
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00:54:02,380 --> 00:54:05,220
the spacecraft and guide
the spacecraft to the surface.
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00:54:11,220 --> 00:54:14,220
There's nothing you can do
at that point to ensure its success
509
00:54:14,220 --> 00:54:15,820
or prevent its crashing...
510
00:54:17,980 --> 00:54:21,180
..and yet you've invested so much
in the outcome.
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00:54:23,740 --> 00:54:27,620
All I could do was sort of curl
up in a ball and wait for the
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00:54:27,620 --> 00:54:30,060
green light that Curiosity was
safely on Mars.
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00:54:33,540 --> 00:54:37,420
Seven years and 2.5 billion
in the making,
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00:54:37,420 --> 00:54:40,020
Curiosity finally touched down
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00:54:40,020 --> 00:54:45,100
at 6.32 Universal Time,
on the 6th of August, 2012.
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00:54:50,340 --> 00:54:52,900
I was sitting in the control room
watching the engineers,
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00:54:52,900 --> 00:54:56,020
who were actually monitoring the
signals coming in from Curiosity,
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00:54:56,020 --> 00:54:58,780
and so they were reading out
the data that they were getting
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00:54:58,780 --> 00:55:01,740
and they detected
the wheels touching the soil.
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00:55:01,740 --> 00:55:04,700
Then a few seconds went
by when cables had to be cut
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00:55:04,700 --> 00:55:06,900
and the rocket jet
pack had to fly away.
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00:55:08,220 --> 00:55:11,020
And, only then, they understood
that Curiosity was safe
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00:55:11,020 --> 00:55:14,460
on the ground, and the whole room
just erupted in celebration.
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00:55:19,380 --> 00:55:23,820
Since it landed, Curiosity
has been exploring Gale Crater
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00:55:23,820 --> 00:55:25,540
for more than six years.
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00:55:28,940 --> 00:55:33,380
Curiosity is a roving laboratory.
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00:55:33,380 --> 00:55:38,540
We actually collect samples
by scooping it or by drilling,
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00:55:38,540 --> 00:55:41,020
or just by sucking in some
of the atmospheric gas.
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00:55:43,180 --> 00:55:47,940
And it's that type of data
that allows us to pick apart
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00:55:47,940 --> 00:55:50,060
the story that those things hold.
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In 2015, we made our first
identification of organic molecules
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00:55:58,180 --> 00:56:00,500
that we think were coming
from the Martian materials.
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00:56:01,860 --> 00:56:04,500
And that is a turning point for us.
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00:56:07,740 --> 00:56:10,220
What we found in those rocks
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00:56:10,220 --> 00:56:13,860
is what we expected
of natural organic matter.
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00:56:13,860 --> 00:56:16,060
It's what you would
expect to find on Earth.
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00:56:18,940 --> 00:56:22,820
Finding the organic matter
is the clue to searching for life.
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00:56:25,380 --> 00:56:27,940
What everybody wants to know
is whether or not Mars
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00:56:27,940 --> 00:56:31,380
once had life, and the short
answer is - we don't know.
540
00:56:32,980 --> 00:56:35,420
The somewhat longer answer is -
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00:56:35,420 --> 00:56:39,860
we see all the signs of materials
that could have supported life.
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00:56:39,860 --> 00:56:42,420
We have evidence for
lots of water early on.
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00:56:44,300 --> 00:56:48,220
We see the nutrients,
we see carbon, we see oxygen,
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00:56:48,220 --> 00:56:50,460
we see nitrogen, we see phosphorus,
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00:56:50,460 --> 00:56:52,660
we see all the stuff that life needs
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00:56:52,660 --> 00:56:57,020
in order to reproduce and survive
as simple microorganisms.
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00:57:01,260 --> 00:57:05,020
For me personally,
I find it might actually
548
00:57:05,020 --> 00:57:07,780
be more surprising if we never
found evidence of life on Mars.
549
00:57:07,780 --> 00:57:10,780
Everything we've found suggests
that Mars was such a friendly,
550
00:57:10,780 --> 00:57:13,740
supportive place for life
in its early history,
551
00:57:13,740 --> 00:57:17,460
and there should be a lot of planets
like that around other stars,
552
00:57:17,460 --> 00:57:19,420
and lots of life in the universe.
553
00:57:19,420 --> 00:57:22,660
So, maybe we're getting to the point
where it'll be more surprising
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00:57:22,660 --> 00:57:24,700
if we never find other life.
555
00:57:30,900 --> 00:57:35,020
And so, thanks to Curiosity's
discoveries, the latest wave
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00:57:35,020 --> 00:57:38,660
of spacecraft might finally
answer the question -
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00:57:38,660 --> 00:57:41,340
has there ever been life on Mars?
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00:57:47,540 --> 00:57:48,860
Next time...
559
00:57:51,140 --> 00:57:54,060
..we enter the realm of the gas
giants...
560
00:57:56,900 --> 00:58:01,580
..to discover how the largest
and oldest of the planets
561
00:58:01,580 --> 00:58:04,100
sculpted the entire solar system.
562
00:58:09,420 --> 00:58:12,180
Jupiter, the godfather.
563
00:58:18,740 --> 00:58:22,020
Journey through our solar system
with this free poster produced
564
00:58:22,020 --> 00:58:26,540
by the Open University, and discover
more about its planets and moons.
565
00:58:28,260 --> 00:58:31,020
Order your free copy by calling...
566
00:58:34,900 --> 00:58:38,180
..or go to...
567
00:58:41,140 --> 00:58:43,660
..and follow the links
to the Open University.
48686
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