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Liftoff ofMessenger on NASA 's
mission to Mercury.
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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 bares 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 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
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is a mystery 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 markings
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that 19th-century astronomers
thought were vegetation,
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even canals bringing meltwater down from
the poles to arid equatorial cities.
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"Across the depths of space,
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"the inhabitants watched us
with envious eyes,"
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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
that it hasn't always been that way.
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Mariner 4 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
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first view 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 in stereo
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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 for the first time...
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Touchdown, we have touchdown.
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- ...and revealed Mars...
- Perfect set-down.
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...like never before.
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And there's the first piece
of information coming in. Oh! Oh!
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The data gathered
over the last 50 years
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has allowed us to create 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
written across its surface,
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and the reason for that
is that there's virtually no erosion.
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There hasn't been for billions of years.
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So the scars of events
that happened even 4 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,
and red and white are high.
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Now, this region here,
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which is much higher, on average,
than the rest of Mars,
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is called Tharsis,
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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 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 to the crater floor
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is nine kilometres.
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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's 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.
And that's a wonderfully evocative name,
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because its surface is sculpted
by flowing water.
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All across the earliest Martian surface,
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we've glimpsed traces 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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...lead by the most audacious Mars mission
ever attempted...
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Vehicle reports entry interface.
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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 decent 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,
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polished 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,
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Curiosity identified the perfect 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
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revealed 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 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,
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
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that there were large bodies
of standing water on Mars
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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.
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So I could have sat on Mars
all those years ago,
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admittedly with a mask to breathe,
cos there was very little oxygen,
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but I could have sat there
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's lakes and seas
had disappeared.
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In our solar system,
only one blue planet survives.
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Mars's 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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4 billion 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
by a cataclysm from space.
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To understand what happened,
we have to look beyond our own world.
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You can't read the deep history
of the Earth by looking at its surface,
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because our planet
is a geologically active world.
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The surface is constantly being re-shaped
by volcanic activity
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and weathering
and the actions of the oceans.
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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 of the solar system
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is written all over its surface.
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The most distinctive feature
of the Moon's surface are its craters.
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It is literally covered
in a record of impacts from space.
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And that allows us to estimate
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the relative ages of different parts
of the Moon.
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And 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 -
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the Moon rocks brought back
by the Apollo astronauts.
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Now, we can estimate the ages of rocks
very precisely
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by looking at the rates of decay
of radioactive elements inside them.
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They are like little stopwatches
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that start ticking
the moment the rocks are formed,
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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
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
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about 3.8 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's 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
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tells us 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
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of the evolution of the solar system,
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and when we do that,
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 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
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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,
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and discounting the, I think,
remote possibility
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that life began elsewhere
in the solar system
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and was transported to the Earth
on meteorites or comets,
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that means that life must have begun here.
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So, somewhere on this planet,
there was a transition from geochemistry,
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the chemistry of Earth,
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to biochemistry, the chemistry of life.
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And whilst the precise details of how that
transition occurred remain a mystery...
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...it's thought that in warm volcanic
pools or deep-sea hydrothermal vents,
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conditions were right
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for the chemical building blocks of life
to form spontaneously.
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And that means that,
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if similar conditions were to be found
elsewhere in the solar system,
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it might be possible
that life began there, too.
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Ignition. And liftoff of the
Atlas V rocket with MRO...
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00:24:27,100 --> 00:24:31,811
...surveying for the deepest insights into
the mysterious evolution of Mars.
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So, in 2005,
NASA embarked on a mission
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to look for those
same environments on Mars.
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For more than a decade,
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the Mars Reconnaissance Orbiter
has been our eyes on the Red Planet...
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...sending back more data
than all the other Mars missions combined.
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MRO has made more than 60,000 orbits,
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mapping over 99% of the planet's surface.
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Its high-resolution cameras
have revealed Mars as never before...
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...discovering polar avalanches...
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...shifting sand dunes...
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...and what could be seasonal
flows of sand
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or even liquid meltwater.
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Then, in 2017,
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MRO turned its gaze to one
of the Red Planet's oldest features,
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the Eridania Basin.
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3.8 billion years ago,
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the basin was a vast sea...
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...holding ten times more water than
the Great Lakes of North America.
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And it was here that MRO found
the evidence it was looking for.
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400-metre thick deposits of minerals
that, on Earth,
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form in deep-sea hydrothermal vents.
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In the Eridania Basin,
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MRO revealed that conditions on Mars
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had once been ripe
for the emergence of life.
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We won't know for sure
whether life began -
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or even perhaps still exists - on Mars
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until we go there
and find physical evidence.
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So microbes buried deep below the soil
in oases of liquid water,
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or maybe microfossils.
243
00:27:46,980 --> 00:27:50,417
But what we do know is that when
life began here on Earth
244
00:27:50,540 --> 00:27:54,534
3.8 billion years ago,
the conditions on Mars were very similar.
245
00:27:54,660 --> 00:27:56,891
There were seas,
there was volcanic activity,
246
00:27:57,020 --> 00:28:01,173
there were even hydrothermal vent systems
on the floors of its oceans.
247
00:28:01,300 --> 00:28:03,019
So it is at least possible
248
00:28:03,140 --> 00:28:08,260
that Earth is not the only world
in the solar system where life began.
249
00:28:14,260 --> 00:28:18,971
The habitable conditions
during what's known as Mars's Noachian Era
250
00:28:19,100 --> 00:28:22,093
persisted for
hundreds of millions of years.
251
00:28:30,780 --> 00:28:37,220
But then prospects for life
on the Red Planet changed dramatically.
252
00:28:42,580 --> 00:28:44,378
Around 3.5 billion years ago,
253
00:28:44,500 --> 00:28:46,617
the Noachian Era drew to a close,
254
00:28:46,740 --> 00:28:51,417
and Mars entered a more frozen,
arid phase known as the Hesperian.
255
00:28:51,540 --> 00:28:55,693
The water that flowed freely
over the surface during the age of Noah
256
00:28:55,820 --> 00:29:00,258
became locked away
in giant reservoirs of ice.
257
00:29:00,380 --> 00:29:04,499
But around the same time,
Mars became more volcanically active,
258
00:29:04,620 --> 00:29:07,533
and the volcanic eruptions
and sub-surface lava flows
259
00:29:07,660 --> 00:29:09,777
occasionally melted the ice,
260
00:29:09,900 --> 00:29:12,540
leading to catastrophic flooding.
261
00:29:12,660 --> 00:29:15,732
They must have been
some of the most spectacular sights
262
00:29:15,860 --> 00:29:17,692
in the history of the solar system.
263
00:29:24,940 --> 00:29:28,092
As molten rock pushed upwards
through the crust,
264
00:29:28,220 --> 00:29:32,692
meltwater poured out onto the surface.
265
00:29:35,380 --> 00:29:38,896
It raged down
from the Southern Highlands...
266
00:29:42,740 --> 00:29:47,895
...until, in a place known
as Echus Chasma,
267
00:29:48,020 --> 00:29:51,775
it plunged over cliffs
four kilometres high...
268
00:30:01,500 --> 00:30:07,770
...creating the largest waterfall the
solar system has ever seen.
269
00:30:47,780 --> 00:30:52,218
Echus Chasma would have been like
no waterfall ever seen on Earth.
270
00:30:52,340 --> 00:30:56,971
350 cubic kilometres of water
flowed over it.
271
00:30:57,100 --> 00:31:01,572
That's like a cube - 70 kilometres
by 70 kilometres by 70 kilometres.
272
00:31:01,700 --> 00:31:03,100
It all emptied into a canyon
273
00:31:03,220 --> 00:31:07,100
10 kilometres wide
and 100 kilometres long,
274
00:31:07,220 --> 00:31:10,099
and that happened in a few weeks.
275
00:31:18,580 --> 00:31:21,857
Once the flood subsided,
the water disappeared...
276
00:31:25,060 --> 00:31:29,612
...leaving the evidence of the falls
etched into the face of the planet.
277
00:31:38,060 --> 00:31:41,053
We don't know precisely why
the climate of Mars
278
00:31:41,180 --> 00:31:44,412
changed from warm and wet
to cold and arid.
279
00:31:44,540 --> 00:31:48,375
We're talking about events
that happened 3.5 billion years ago
280
00:31:48,500 --> 00:31:51,618
on a planet hundreds of millions
of kilometres away.
281
00:31:51,740 --> 00:31:54,175
So it is a hard problem.
282
00:31:54,300 --> 00:31:56,053
But we do strongly suspect
283
00:31:56,180 --> 00:31:59,139
that changes happening
on the planet's surface were driven,
284
00:31:59,260 --> 00:32:00,580
at least in part,
285
00:32:00,700 --> 00:32:03,534
by changes in the planet's interior.
286
00:32:10,620 --> 00:32:13,260
Deep within Mars's core,
287
00:32:13,380 --> 00:32:17,215
something was causing the planet to die,
288
00:32:17,340 --> 00:32:22,131
and the evidence can be found
in Mars's atmosphere.
289
00:32:22,260 --> 00:32:24,252
T minus ten, nine,
290
00:32:24,380 --> 00:32:28,340
eight, seven, six, five, four,
291
00:32:28,460 --> 00:32:31,658
three, two, one...
292
00:32:31,780 --> 00:32:33,214
Main engines start.
293
00:32:33,340 --> 00:32:37,892
Ignition.
And liftoff of the Atlas V with MAVEN,
294
00:32:38,020 --> 00:32:43,049
looking for clues about the evolution
of Mars through its atmosphere.
295
00:32:48,460 --> 00:32:50,258
In September 2014,
296
00:32:50,380 --> 00:32:54,818
NASA's MAVEN probe
made its final approach to the Red Planet.
297
00:33:09,580 --> 00:33:11,219
Its mission -
298
00:33:11,340 --> 00:33:15,050
to understand what drove
the planet's dramatic climate change.
299
00:33:28,300 --> 00:33:30,212
MAVEN is equipped
with an array of instruments
300
00:33:30,340 --> 00:33:33,936
designed to measure the behaviour
of the atoms and molecules
301
00:33:34,060 --> 00:33:35,540
in Mars's atmosphere.
302
00:34:27,580 --> 00:34:31,096
The spacecraft circles Mars
in an elliptical orbit...
303
00:34:39,340 --> 00:34:42,777
...allowing it to measure the full profile
304
00:34:42,900 --> 00:34:44,414
of the planet's upper atmosphere.
305
00:34:52,700 --> 00:34:57,536
At its lowest point, it's just
150 kilometres above the surface.
306
00:35:01,100 --> 00:35:04,776
At its highest,
a little over 6,000 kilometres.
307
00:35:08,500 --> 00:35:11,698
And it was at the very top
of Mars's atmosphere
308
00:35:11,820 --> 00:35:16,656
that MAVEN found the key to the mystery
of what happened to Mars.
309
00:35:22,460 --> 00:35:24,417
Detailed measurements revealed
310
00:35:24,540 --> 00:35:27,374
gas is being lost
from the Martian atmosphere,
311
00:35:27,500 --> 00:35:30,334
escaping to space
312
00:35:30,460 --> 00:35:34,010
at a rate of about two kilograms
every second.
313
00:35:39,300 --> 00:35:44,898
Over time, it's thought this gradual
stripping away of Mars's atmosphere
314
00:35:45,020 --> 00:35:49,060
has slowly thinned the insulating layer
surrounding the planet...
315
00:35:52,020 --> 00:35:55,457
...causing surface temperatures
to plummet.
316
00:36:13,260 --> 00:36:17,174
But what was it that caused Mars
to lose its atmosphere
317
00:36:17,300 --> 00:36:20,020
while Earth clung onto hers?
318
00:36:28,620 --> 00:36:33,376
150 million kilometres away
in that direction is the setting Sun -
319
00:36:33,500 --> 00:36:35,537
a giant nuclear fusion reactor.
320
00:36:35,660 --> 00:36:37,856
You could fit a million Earths inside it.
321
00:36:37,980 --> 00:36:42,418
Now, the surface temperature
is only around 6,000 degrees Celsius,
322
00:36:42,540 --> 00:36:44,771
but the Sun's atmosphere,
known as its corona,
323
00:36:44,900 --> 00:36:46,573
is at a million degrees.
324
00:36:46,700 --> 00:36:49,100
And that means it's in the form of
what's known as a plasma -
325
00:36:49,220 --> 00:36:51,780
a soup of electrically charged particles.
326
00:36:51,900 --> 00:36:54,540
Now, some of those particles
are moving around so fast
327
00:36:54,660 --> 00:36:55,855
that they can escape,
328
00:36:55,980 --> 00:36:59,132
and they stream away
in what's known as the solar wind.
329
00:36:59,260 --> 00:37:02,890
They reach the Earth travelling
at a few hundred kilometres per second,
330
00:37:03,020 --> 00:37:07,173
and if we weren't protected,
they would strip away our atmosphere.
331
00:37:16,740 --> 00:37:19,380
And when the Sun dips below the horizon...
332
00:37:21,900 --> 00:37:26,656
...there are times when that protective
force field is revealed.
333
00:37:46,100 --> 00:37:47,375
Just look at that!
334
00:37:48,580 --> 00:37:50,219
I mean, there is the aurora.
335
00:37:54,380 --> 00:37:58,090
It's the laws of nature,
all of them, written across the sky.
336
00:38:01,980 --> 00:38:05,337
Electrically charged particles
are being driven away from the Sun,
337
00:38:05,460 --> 00:38:10,330
ultimately from nuclear fusion reactions
in the core of a star.
338
00:38:10,460 --> 00:38:14,249
They're crossing the solar system,
hitting the Earths magnetic field,
339
00:38:14,380 --> 00:38:18,135
stretching it out
on the dark side of the planet.
340
00:38:18,260 --> 00:38:21,571
The field then snaps back
like an elastic band,
341
00:38:21,700 --> 00:38:26,058
accelerating all those charged particles
up and down the field lines
342
00:38:26,180 --> 00:38:31,209
to the poles, which is here,
in the skies over Iceland,
343
00:38:31,340 --> 00:38:36,051
and they hit nitrogen and oxygen molecules
in the atmosphere...
344
00:38:37,660 --> 00:38:39,652
And you're seeing quantum mechanics.
345
00:38:39,780 --> 00:38:41,294
They're exciting the molecules
346
00:38:41,420 --> 00:38:44,572
so that they emit light
in characteristic colours.
347
00:38:56,940 --> 00:39:00,854
And if you think about it,
this is the only time that we really see
348
00:39:00,980 --> 00:39:02,414
the Earth's magnetic field.
349
00:39:04,460 --> 00:39:07,692
It's one of the reasons why life on Earth
350
00:39:07,820 --> 00:39:10,619
has been able to persist
for 4 billion years.
351
00:39:13,100 --> 00:39:16,332
So, in a sense,
that's the reason that you exist.
352
00:39:21,740 --> 00:39:25,256
It's Earth's magnetic field
that protects our atmosphere
353
00:39:25,380 --> 00:39:27,895
from the ravages of the solar wind,
354
00:39:28,020 --> 00:39:32,970
and that protective shield has its origins
deep in the planet's interior.
355
00:39:35,620 --> 00:39:38,818
Thousands of kilometres down,
below my feet -
356
00:39:38,940 --> 00:39:40,897
actually below your feet now -
357
00:39:41,020 --> 00:39:42,613
is the Earth's outer core,
358
00:39:42,740 --> 00:39:45,778
which is a seething mass of molten iron.
359
00:39:45,900 --> 00:39:49,496
Now, convection currents
cause the molten iron to rise,
360
00:39:49,620 --> 00:39:53,773
then the Earth's rotation causes it
to spiral around.
361
00:39:53,900 --> 00:39:58,497
Now, a spiralling, circling flow of an
electrically conducting liquid
362
00:39:58,620 --> 00:40:00,339
is a dynamo.
363
00:40:00,460 --> 00:40:02,895
A dynamo generates a magnetic field,
364
00:40:03,020 --> 00:40:06,934
and the Earth's field rises up
not just to the surface here
365
00:40:07,060 --> 00:40:10,610
but out into space,
forming our protective shield.
366
00:40:10,740 --> 00:40:13,460
And that... what you see there.
367
00:40:20,740 --> 00:40:22,254
And just like Earth,
368
00:40:22,380 --> 00:40:26,294
ancient Mars was also shielded
from the Sun.
369
00:40:32,860 --> 00:40:35,853
Aurora once danced above its poles...
370
00:40:39,100 --> 00:40:43,936
...keeping guard over the
Martian atmosphere and seas below.
371
00:40:59,500 --> 00:41:06,054
But between 3.5 and 4 billion years ago,
Mars's dynamo switched off.
372
00:41:08,820 --> 00:41:12,370
The aurora surrounding the poles
slowly faded away,
373
00:41:12,500 --> 00:41:14,651
as the magnetic field diminished...
374
00:41:17,220 --> 00:41:21,612
...allowing the atmosphere
to be stripped away by the solar wind.
375
00:41:31,260 --> 00:41:35,015
Without protection,
seas evaporated,
376
00:41:35,140 --> 00:41:37,291
the surface froze,
377
00:41:37,420 --> 00:41:41,209
and Mars was transformed.
378
00:41:49,180 --> 00:41:53,060
At the same time,
the fortunes of Mars's sister world
379
00:41:53,180 --> 00:41:55,456
were about to take a very different turn.
380
00:41:59,820 --> 00:42:01,698
For the next billion years or so,
381
00:42:01,820 --> 00:42:05,814
Earth was indistinguishable
from the landscapes of early Mars -
382
00:42:05,940 --> 00:42:09,172
barren continents surrounded by ocean.
383
00:42:09,300 --> 00:42:10,780
But in Earth's oceans,
384
00:42:10,900 --> 00:42:13,972
life was beginning to transform
the planet.
385
00:42:17,580 --> 00:42:22,018
Primitive algae started to neutralise
the ocean's acidity
386
00:42:22,140 --> 00:42:28,296
and replace the dense red fog of Earth's
methane-rich atmosphere with oxygen.
387
00:42:31,620 --> 00:42:33,612
Around 600 million years ago,
388
00:42:33,740 --> 00:42:35,572
that oxygen-rich atmosphere
389
00:42:35,700 --> 00:42:38,534
allowed complex life
to evolve in the oceans,
390
00:42:38,660 --> 00:42:40,094
colonise the land,
391
00:42:40,220 --> 00:42:45,215
and ultimately produce this almost
infinitely rich living world today
392
00:42:45,340 --> 00:42:48,572
of which we are a part.
393
00:42:59,220 --> 00:43:03,180
While Mars died, Earth flourished.
394
00:43:09,540 --> 00:43:14,615
To understand why the two sisters
had such different destinies,
395
00:43:14,740 --> 00:43:20,099
you have to go right back
to the time the planets were forming.
396
00:43:25,300 --> 00:43:27,178
When Mars and Earth were born,
397
00:43:27,300 --> 00:43:31,852
the solar system was a chaotic vortex
of gas and rock.
398
00:43:36,540 --> 00:43:39,180
Material clumped together and grew...
399
00:43:40,580 --> 00:43:42,890
...only to be smashed apart.
400
00:43:50,260 --> 00:43:53,617
Over time, some of the objects became
large enough to survive
401
00:43:53,740 --> 00:43:57,177
at least the smaller impacts
and continue to grow,
402
00:43:57,300 --> 00:44:00,577
including the embryonic planets
Earth and Mars.
403
00:44:09,580 --> 00:44:13,256
But there was one crucial difference
between the young planets.
404
00:44:20,660 --> 00:44:23,220
Mars formed
in a region of the solar system
405
00:44:23,340 --> 00:44:25,900
with considerably less rocky material...
406
00:44:27,300 --> 00:44:30,532
...and that had a profound impact
on the planet's growth.
407
00:44:36,020 --> 00:44:38,410
Mars is a significantly smaller world -
408
00:44:38,540 --> 00:44:40,930
it's about half
the diameter of the Earth -
409
00:44:41,060 --> 00:44:43,052
and that makes all the difference.
410
00:44:43,180 --> 00:44:46,093
Although the details
are not yet fully understood,
411
00:44:46,220 --> 00:44:48,860
it seems clear that Mars's smaller size
412
00:44:48,980 --> 00:44:52,894
meant that its dynamo switched off
many billions of years ago.
413
00:44:56,580 --> 00:45:01,052
Being smaller meant Mars's core cooled
more quickly than Earth's.
414
00:45:03,940 --> 00:45:08,810
And this is certainly part of the reason
why Mars lost its magnetic field.
415
00:45:15,980 --> 00:45:18,939
Even though the planet is further away
from the Sun than we are,
416
00:45:19,060 --> 00:45:24,089
that meant that the solar wind stripped
away its atmosphere, and Mars died.
417
00:45:24,220 --> 00:45:29,420
So even though Earth and Mars
are so similar in so many ways,
418
00:45:29,540 --> 00:45:33,295
the difference in position and size
in the solar system
419
00:45:33,420 --> 00:45:35,889
lead to very different fates.
420
00:45:46,300 --> 00:45:50,089
Long ago, two sister worlds were born.
421
00:45:55,100 --> 00:45:59,219
In childhood, Mars was warm and wet...
422
00:46:03,700 --> 00:46:08,570
...whilst the Earth
was inhospitable and toxic.
423
00:46:16,660 --> 00:46:21,735
Both young planets survived the violence
of the Late Heavy Bombardment...
424
00:46:23,700 --> 00:46:26,659
...emerging as mature worlds...
425
00:46:28,180 --> 00:46:32,732
...primed with all
the ingredients for life.
426
00:46:41,180 --> 00:46:45,618
But deep inside,
the smaller of the two was dying.
427
00:46:52,260 --> 00:46:54,297
Mars's seas dried up.
428
00:47:06,620 --> 00:47:09,692
And as the planet's interior cooled,
429
00:47:09,820 --> 00:47:13,496
one by one, her fires went out.
430
00:47:18,180 --> 00:47:22,333
Olympus Mons, the largest volcano
in the solar system,
431
00:47:22,460 --> 00:47:26,136
last erupted around 25 million years ago.
432
00:47:35,060 --> 00:47:37,973
As the lava turned to stone,
433
00:47:38,100 --> 00:47:41,491
Mars was frozen in time.
434
00:47:56,300 --> 00:48:02,536
And so, today, her surface lies rusted
and gathering dust.
435
00:48:10,460 --> 00:48:14,249
But that might not be
the end of Mars's story.
436
00:48:21,260 --> 00:48:26,699
Because the next generation of spacecraft
are already on their way.
437
00:48:33,780 --> 00:48:36,932
NASA Orion -
438
00:48:37,060 --> 00:48:39,575
currently in advanced testing.
439
00:49:09,300 --> 00:49:12,099
ESA Exomars -
440
00:49:12,220 --> 00:49:16,976
a fleet of spacecraft
designed to search for signs of life.
441
00:49:25,900 --> 00:49:31,294
And the most ambitious
private space mission ever conceived.
442
00:49:41,100 --> 00:49:47,620
A launch vehicle developed to take humans
to the surface of Mars.
443
00:50:05,020 --> 00:50:07,580
Mars is, in a sense, a failed world,
444
00:50:07,700 --> 00:50:12,331
a faded ember etched with the memories
of a more enticing past,
445
00:50:12,460 --> 00:50:17,615
but there have been - and may still be -
life on Mars,
446
00:50:17,740 --> 00:50:21,370
and the discovery of a second genesis
in our solar system
447
00:50:21,500 --> 00:50:25,938
would have profound philosophical,
scientific and cultural consequences,
448
00:50:26,060 --> 00:50:31,260
because it would mean there is a sense
of inevitability about the origin of life.
449
00:50:31,380 --> 00:50:35,374
And that would mean that the universe
is most likely teeming with life,
450
00:50:35,500 --> 00:50:37,890
that we are not alone.
451
00:50:42,940 --> 00:50:45,535
But equally importantly, I think,
452
00:50:45,660 --> 00:50:51,054
is the role that a planet with a history
like Mars could play in our future.
453
00:50:51,180 --> 00:50:53,012
Mars is rich in resources.
454
00:50:53,140 --> 00:50:56,770
It has vast reservoirs of frozen water
below the surface
455
00:50:56,900 --> 00:51:00,860
and minerals - iron, nitrogen,
carbon, oxygen -
456
00:51:00,980 --> 00:51:04,018
all the things you need
to support a civilisation.
457
00:51:06,140 --> 00:51:10,100
And that's why I think that,
in my lifetime, there will be Martians.
458
00:51:10,220 --> 00:51:12,576
But the Martians will be us.
459
00:51:12,700 --> 00:51:15,898
We will go to Mars and make it our home,
460
00:51:16,020 --> 00:51:20,253
and that old red world will become
our first step beyond the cradle
461
00:51:20,380 --> 00:51:23,020
and out to the stars.
462
00:51:54,780 --> 00:52:00,811
Mars really captures our imagination,
463
00:52:00,940 --> 00:52:03,978
partly because it's so close.
464
00:52:04,100 --> 00:52:06,899
I think people are really interested
in Mars
465
00:52:07,020 --> 00:52:11,014
because it actually is so similar
to Earth.
466
00:52:11,140 --> 00:52:17,091
It's close by, it's easy to travel there
with robots and space missions,
467
00:52:17,220 --> 00:52:19,974
and so we've done a lot of exploration,
468
00:52:20,100 --> 00:52:23,696
and every time you go and look,
you discover something new.
469
00:52:27,780 --> 00:52:32,013
NASA Curiosity launched
on 26th November 2011.
470
00:52:34,980 --> 00:52:39,657
But the biggest obstacle facing
the mission team wasn't leaving the Earth.
471
00:52:42,820 --> 00:52:44,413
Mars has a unique set of challenges
472
00:52:44,540 --> 00:52:46,816
compared to other places
we go with spacecraft.
473
00:52:46,940 --> 00:52:49,375
Mars has an atmosphere, but it's thin,
474
00:52:49,500 --> 00:52:52,015
so it's not enough
to really slow you down,
475
00:52:52,140 --> 00:52:54,974
but it is enough to actually burn you up
as you're trying to land.
476
00:52:57,580 --> 00:53:00,379
Curiosity reached
the top of the Martian atmosphere
477
00:53:00,500 --> 00:53:04,130
travelling at 20,000 kilometres per hour.
478
00:53:06,340 --> 00:53:10,095
Curiosity is a big rover - it weighs
a metric tonne - and so landing that
479
00:53:10,220 --> 00:53:12,316
required every trick in the book
of how we've learned to land on Mars
480
00:53:12,340 --> 00:53:13,774
with previous missions.
481
00:53:16,620 --> 00:53:19,772
To land safely,
the rover had to be slowed
482
00:53:19,900 --> 00:53:22,460
to less than four kilometres per hour.
483
00:53:31,060 --> 00:53:33,236
You end up arriving at
Mars going really fast,
484
00:53:33,260 --> 00:53:34,819
so you actually have to slow down,
485
00:53:34,940 --> 00:53:37,535
and we do that using a heat shield,
486
00:53:37,660 --> 00:53:40,812
which burns off a lot of energy
and creates a lot of heat,
487
00:53:40,940 --> 00:53:44,570
so you have to absorb that somehow
and not damage the spacecraft.
488
00:53:44,700 --> 00:53:46,373
Then a parachute comes out.
489
00:53:50,300 --> 00:53:53,259
The biggest parachute
we've ever used in a planetary mission.
490
00:53:55,660 --> 00:53:58,050
And that even doesn't slow Curiosity
down enough,
491
00:53:58,180 --> 00:53:59,716
because Mars's atmosphere
is quite thin,
492
00:53:59,740 --> 00:54:01,971
so then rockets carry the spacecraft
493
00:54:02,100 --> 00:54:04,057
and guide the spacecraft
to the surface.
494
00:54:10,300 --> 00:54:13,020
There's nothing you can do
at that point to ensure its success
495
00:54:13,140 --> 00:54:14,779
or prevent its crashing.
496
00:54:17,300 --> 00:54:20,020
And yet, you've invested so much
in the outcome.
497
00:54:22,820 --> 00:54:24,618
All I could do
was sort of curl up in a ball
498
00:54:24,740 --> 00:54:29,292
and wait for the green light
that Curiosity was safely on Mars.
499
00:54:32,180 --> 00:54:35,935
Seven years
and $2.5 billion in the making,
500
00:54:36,060 --> 00:54:39,371
Curiosity finally touched down
501
00:54:39,500 --> 00:54:44,211
at 6:32 Universal Time
on 6th August 2012.
502
00:54:49,300 --> 00:54:50,734
I was sitting in the control room,
503
00:54:50,860 --> 00:54:52,897
watching the engineers
who were actually monitoring
504
00:54:53,020 --> 00:54:54,693
the signals coming in from Curiosity,
505
00:54:54,820 --> 00:54:57,733
and so they were reading out
the data that they were getting,
506
00:54:57,860 --> 00:55:00,694
and they detected
the wheels touching the soil.
507
00:55:00,820 --> 00:55:03,972
Then a few seconds went by
when cables had to be cut
508
00:55:04,100 --> 00:55:05,700
and the rocket jet pack had to fly away.
509
00:55:07,220 --> 00:55:10,657
And only then they understood
that Curiosity was safe on the ground,
510
00:55:10,780 --> 00:55:14,376
and the whole room
just erupted in celebration.
511
00:55:18,700 --> 00:55:19,975
Since it landed,
512
00:55:20,100 --> 00:55:24,219
Curiosity has been exploring
Gale Crater for more than six years.
513
00:55:28,180 --> 00:55:32,140
Curiosity is a roving laboratory.
514
00:55:32,260 --> 00:55:37,289
We actually collect samples by scooping it
or by drilling
515
00:55:37,420 --> 00:55:40,140
or just by sucking in
some of the atmospheric gas.
516
00:55:42,260 --> 00:55:45,890
And it's that type of data that allow us
517
00:55:46,020 --> 00:55:49,491
to peck apart the story
that those things hold.
518
00:55:51,780 --> 00:55:56,297
In 2015, we made our first identification
of organic molecules
519
00:55:56,420 --> 00:55:59,697
that we think were coming
from the Martian materials.
520
00:56:01,220 --> 00:56:03,655
And that is a turning point for us.
521
00:56:06,980 --> 00:56:09,370
What we found in those rocks
522
00:56:09,500 --> 00:56:12,857
is what we expected
of natural organic matter.
523
00:56:12,980 --> 00:56:15,176
It's what you would expect to find
on Earth.
524
00:56:18,100 --> 00:56:22,253
Finding the organic matter
is the clue to searching for life.
525
00:56:24,500 --> 00:56:27,857
What everybody wants to know
is whether or not Mars once had life,
526
00:56:27,980 --> 00:56:30,495
and the short answer is,
we don't know.
527
00:56:31,900 --> 00:56:33,619
The somewhat longer answer is,
528
00:56:33,740 --> 00:56:38,610
we see all the signs of materials
that could have supported life.
529
00:56:38,740 --> 00:56:41,778
We have evidence
for lots of water early on.
530
00:56:43,460 --> 00:56:44,689
We see the nutrients.
531
00:56:44,820 --> 00:56:47,176
We see carbon. We see oxygen.
532
00:56:47,300 --> 00:56:50,054
We see nitrogen. We see phosphorus.
533
00:56:50,180 --> 00:56:54,299
We see all the stuff that life needs
in order to reproduce and survive
534
00:56:54,420 --> 00:56:56,093
as simple microorganisms.
535
00:57:00,140 --> 00:57:01,813
For me, personally,
536
00:57:01,940 --> 00:57:04,580
I find it might actually be
more surprising
537
00:57:04,700 --> 00:57:06,692
if we never found evidence
of life on Mars.
538
00:57:06,820 --> 00:57:08,300
Everything we've found suggests
539
00:57:08,420 --> 00:57:12,573
that Mars was such a friendly, supportive
place for life in its early history,
540
00:57:12,700 --> 00:57:16,376
and there should be a lot of planets
like that around other stars
541
00:57:16,500 --> 00:57:18,378
and lots of life in the universe.
542
00:57:18,500 --> 00:57:21,459
So maybe we're getting to the point
where it'll be more surprising
543
00:57:21,580 --> 00:57:24,095
if we never find other life.
544
00:57:29,980 --> 00:57:32,734
And so,
thanks to Curiosity's discoveries,
545
00:57:32,860 --> 00:57:37,571
the latest wave of spacecraft
might finally answer the question,
546
00:57:37,700 --> 00:57:40,215
has there ever been life on Mars?