Should We Go to Mars? The Big Think

Mars, the Red Planet.

For millennia, an object of mystery,

intrigue and fantasy.

But now it's more than that.

It's the next target in the human exploration of space.

It's a thrilling prospect, but how likely are we to succeed?

And is it a journey we should even be attempting?

With a career spanning medicine, astrophysics and aeronautics,

Dr Kevin Fong is uniquely placed to explore the incredible challenges

that a human mission to Mars would pose.

This is going to be the most risky human expedition in the history of our species.

The Red Planet, Mars. For over 2,000 years, the symbol for war.

Now, with the help of the BBC's archive...

We've just had some amazing photographs sent back by the American probe

to Mars, Mariner 6.

..Kevin is going to explore what we'll need to do if we are to succeed.

It cannot happen without your ability to integrate stuff in low Earth orbit.

It cannot happen without international cooperation.

It's a journey that will test technology and human survival to their limits.

No-one knows if it's possible.

That isolation, that feeling of isolation,

partly because of the delay in communications, will be quite intense.

It's a debate that, for Kevin, pushes the limits of technology,

the extremes of human endurance and explores the very idea of what it is

to be human.

Go, Atlas. Go, Centaur.

We're in the early days of a new space race.

This time, the target is Mars.

But it isn't the Russians going toe to toe with Nasa,

it's private companies taking their first steps into space.

No-one is better qualified to explore the challenge of our first

human expedition to Mars than Dr Kevin Fong.

He's trained and worked with Nasa,

and he's researched human survivability in extreme environments to better

understand the challenges of human space missions.

The effects of altitude are pretty obvious.

With the race to Mars well and truly under way,

Kevin will dissect the unique challenges such a mission would face,

explore the reasons for going,

encounter powerful arguments against a human mission to Mars and,

in so doing, make his case for the toughest journey humanity will have ever attempted.

The first problem with Mars is that history is against us.

Our robotic spacecraft have been there many times already,

with decidedly mixed results.

We've been firing stuff at Mars for more than half a century now.

The first missions went in the 1960s.

And we've slowly been building up this collage of evidence about what

Mars is like.

The very first spacecraft to reach the Red Planet was Nasa's Mariner 4 probe.

As Mariner 4 swept past Mars,

its black and white television camera snapped 22 close-up pictures of the planet.

These images, the first-ever digital television pictures,

were stored on a tape recorder.

Then they had to be radioed back to Earth.

But the early successes of the Mariner probes paint a false picture,

because Mars is littered with the wreckage of failure.

The history of Mars exploration is pretty chequered.

It's actually worse than 50/50, our success rate there.

It's more like one in every three objects that we throw at Mars actually

gets there and completes its mission.

Nasa's Mariner 3 and Mariner 8 probes were both destroyed shortly after launch.

But the Russians suffered the worst losses,

failing with every attempt they made to reach Mars between 1960 and 1971.

Then, in the 1990s, it was the Americans' turn to hit trouble again.

Two high-profile missions went wrong,

the first in an almost comically inept way.

Now, it's a mistake many of us have made,

but then most of us aren't in charge of missions into space.

Scientists at Nasa couldn't work out why the Mars Orbiter,

worth a small £78 million, got lost in space,

until someone pointed out that they'd planned everything in feet and inches

rather than metres and centimetres.

Only three months later, another mission, and more bad news.

American space agency Nasa is on the verge of having to admit to another

embarrassing failure.

The Mars Polar lander would be the second spacecraft that it's lost in

-just two months.

-Three days on, and still no sign of their lost lander.

Nasa engineers had thought it was just a case of a misdirected

communications antenna.

Now it looks likely that the spacecraft could be seriously damaged.

The 21st century has brought little improvement in our success rate.

In 2003, the British Beagle 2 lander was lost,

apparently destroyed on impact with the Martian surface.

And in 2016, the Schiaparelli lander came to an even more violent end,

its remains now smeared across the Martian landscape.

Given this patchy and, at times, embarrassing track record,

should we really be planning to send humans to Mars?

To travel to Mars,

you're talking about crossing hundreds of millions of miles of

interplanetary space,

screaming into a re-entry at thousands of kilometres an hour, and then trying

to land on the surface of a planet on your own with no real direct input

from Earth, after months and months of journeying.

That's hard enough to do with unmanned vehicles.

So it's going to be a significant challenge for human crews.

Superficially, our record of sending humans into space gives cause for optimism.

Apollo was a triumph.

But since Apollo, it can be argued that we've regressed.

Since December 1972,

when Apollo 17 blasted off from Taurus-Littrow crater,

no human has ventured more than 250 miles from the surface of the Earth.

Britain's first astronaut, Helen Sharman, disagrees.

She feels our experiences with the International Space Station and

the space shuttle have been the perfect preparation for sending humans to Mars.

We've learnt technically how to create more reliable spacecraft,

how to create better cooling systems,

how to generate energy in different ways.

So there's lots that we've learnt, and it will provide us in good stead

for the future.

Despite the failure of many robotic missions to Mars,

we have made some progress in human space flight.

But there's no getting away from the scale of the challenge.

The first big problem happens right at the start of the mission.

Sending humans to Mars will require some seriously heavy lifting.

Putting Apollo into space required the biggest and most powerful rockets

ever built. But they're puny compared to what will be needed for Mars.

When you're talking about exploring Mars, it's all about how much you want to take with you,

what you want to pack to go there, who you want to go.

It's about the mass that you want to deliver to the surface of Mars.

And so every kilo you want to take to Mars requires tens - if not hundreds -

of kilos of equipment to move it to low Earth orbit.

It's estimated that even a modest crewed mission to Mars will require

a payload of 40 tonnes.

That's 40 times what was needed to send the Curiosity rover to Mars.

And just getting that off the ground would be a mammoth task.

Climbing out of the deep gravity well,

that huge force of attraction around a planet like Earth,

is the most difficult bit.

It requires an explosive release of energy, massive energy,

energy comparable to the size of a small nuclear weapon,

to get a vehicle and her crew into low Earth orbit.

And so in human space flight, in all of space flight,

the first 250 miles are the hardest 250 miles.

Several different approaches are being planned.

We have lift-off at the Falcon 9.

Miraculous. That's first-stage acceleration.

SpaceX, brainchild of South African entrepreneur Elon Musk,

is banking on small,

lightweight reusable rockets that can shuttle payload into orbit

and then come back to pick up more,

though early test results have been mixed.

And then there's Nasa.

With the Apollo programme Saturn V rocket as their template,

they've decided to take an unashamedly American route

by going large.

Nasa's rocket is called the Space Launch System or SLS.

And when it's complete, it will be the largest and most powerful rocket ever built.

It's so much larger than what we did here before, so much taller.

The best way to assemble something this complex and this big is to

assemble it vertically.

This is as high as we can go using the elevator.

The rest is on foot.

It's hard to tell, with this big of a space,

how big the actual vehicle's going to be, the rocket.

You can actually already see some signs emerging.

You can see that blue circle forming.

That is the actual diameter of the rocket.

And even at this height, we cannot contain the entire rocket.

In Stennis, Mississippi,

Nasa test the rocket engines that will power the SLS into space.

An engine like this will be just one of six which will help propel the SLS into orbit.

So when the time comes to test the much bigger SLS rocket,

it must be at the largest stand they have.

Like so much in the mission to Mars,

they'll be standing on the shoulders of Nasa's previous missions,

borrowing and repurposing the best from Apollo and the shuttle.

-How's it going, man?

-It's going good.

-All right.

B Stand was built over 50 years ago to test the Saturn rockets that

carried the Apollo missions to space.

Gary Benton and his team will be reshaping and upgrading this stand

so that it can cope with the next generation of rockets.

This is the same crane that we used to lift those Saturn V core stages,

and we're going to use that very same crane

to lift up the SLS core stage and place it

in this facility, anchor it down really good,

fire off about two million pounds of thrust, and that's going to be

the biggest test we've done out here since we did the Saturn V.

There's a palpable sense of excitement here,

because, for the first time in decades,

they're thinking of using these rockets to send people beyond Earth's orbit.

For now, this is Nasa's best vision of what a rocket bound for Mars

-would look like.

-T-minus ten, nine, eight, seven, six, five...

But the first complete SLS rocket is still a distant dream,

and it gets worse.

Nasa estimates they will need seven SLS launches for a single Mars

mission so the huge Mars spacecraft can be pieced together in space.

But at least this problem is just a question of brute strength.

Throw enough money at it, and solutions should be found.

But the next stage of the journey poses a very different set of challenges.

There's an uncomfortable truth about the journey to Mars.

At a minimum of 34 million miles, 120 times more distant than the moon,

it's two orders of magnitude further than any journey humans have ever made before.

With existing technology, if you're using chemical propulsion,

then a journey to Mars is between six and nine months in one direction,

so from Earth to Mars.

And then you have to sit on Mars and wait for the right planetary alignments

to be able to get back, and those come up at about 30 days or so,

and then again about a year and a half later.

So the shortest mission that you could hope for for Mars is just over

a year. The longest ones are approaching three years.

A three-year mission would be nearly triple the length of anything we've

done before, and spending that long in space poses some serious risks.

The first problem is radiation.

Just how much radiation you would be exposed to on a mission to Mars was

quantified by the recent Curiosity mission,

and they found it to be several hundred times more intense than on Earth.

And that's a problem.

One important factor of life on Earth and how we were able to evolve

is that we're protected from the radiation

of galactic cosmic rays and from the radiation

of the sun by the magnetic field of the Earth,

which is caused by the iron core of the Earth.

That magnetic field creates a protective shield around our planet called

the magnetosphere, which deflects radiation.

The more dangerous solar particles don't get through.

Those that do create the spectacular light show of the aurora.

But out in space, everything is different.

Out here, the bubbling surface of the sun occasionally builds to a huge explosion.

These solar flares throw out massive bursts of radiation and high-energy

protons which might damage your DNA,

causing mutations and cancer later in life.

Protecting against radiation will be crucial if we are to successfully

send people to Mars.

What we need is a material that can shield astronauts in the event of a

solar storm, but doesn't add extra weight to the spacecraft.

Nasa's answer is to use something they will already be carrying,

a material known for its ability to absorb solar radiation...

Water.

So we're looking at taking a garment and filling it with water,

which you see a first concept of here, of this astronaut

with a water wall built into its wearable garment.

So this is something that you'd fill for an event.

So he gets protection in maybe a different form,

but with a lot less mass penalty to it.

Unfortunately for Martian astronauts,

radiation will only be the start of the problems.

An even more pernicious threat begins only minutes after launch.

Now let's try backwards.

Your body starts to experience weightlessness

as soon as you get into low Earth orbit,

and that starts modifying your body from the moment you deploy in space.

And that has effects on your bones and your muscles,

because those go to waste very quickly.

The answer, for now, is exercise - and lots of it.

Something that Libby Jackson knows only too well from her days as flight director

of the International Space Station's Columbus science module.

The crew on board the International Space Station have to exercise for

about two hours every day.

That's about an hour of cardio

and an hour of what we would call weights.

They're not lifting weights, you can't do that in a weightless

environment, but they have a hydraulic ram that gives them resistance.

You need to keep your body in a condition

that allows you to function when you get to Mars.

But Kevin favours a different approach to the problem of zero gravity...

..one that will require a major technological leap.

We take our light, our heat, our power, our water, our food,

we take even our atmosphere with us.

So why don't we take gravity?

Now it turns out that that's not as sci-fi as it sounds.

You can do that by building a large rotating vehicle.

I'm talking about a vehicle about the size of the London Eye that would spin

about four times a minute.

That would be enough to provide this level of gravity,

a 1G Earth gravitational load.

And that would wash away an awful lot of our problems.

An artificial gravity device of this kind may have its benefits,

but it would add huge cost and weight to an already difficult mission.

The third huge challenge is that sense of isolation from the world,

not being able to get back easily.

Unlike the physical threats that have the potential to be managed with technology,

the psychological dangers of a journey to Mars are much harder

to quantify.

Astronauts will have to deal with the twin challenges of isolation from

their loved ones on Earth

and close confinement with their fellow crewmates.

One of my favourite quotes is from Valery Ryumin,

who was a Russian who flew their Salyut space station missions

in the 1970s, I think in 1976.

He said all the conditions necessary for murder were met

if you lock two people in a cabin for three months.

These missions are going to be up to 30 months, a very testing time.

Engines on. Five, four, three, two, one.

All engines running.

Liftoff! We have liftoff.

Picking a crew for a journey of this length will be tricky.

Back in the days of Apollo 11, astronaut recruitment was straightforward.

It was clear who had the right stuff.

Neil Armstrong,

Buzz Aldrin and Michael Collins were the cream of US supersonic flight.

They were drawn from the elite world of fighter and test pilots,

and with that came supreme hand-eye coordination and physical daring.

But these may not be the same skills you'd need to go to Mars.

I noticed that a lot of the astronauts were of the old school.

"I hunt, I fish, I climb mountains."

You know, lots of outdoor stuff.

But think about a mission to Mars.

Is it outdoor stuff, or is it confinement?

And then I see somebody that says "I have a stamp collection,

"I do a lot of reading, I enjoy watching movies,"

and I'm thinking, "That might be good for confinement."

Dr David Dinges is interested in how you select a crew

and safeguard their psychological welfare in space.

The key issue is understanding who's going to develop a problem

and when it will develop. Will all the crew develop it?

How do we detect it?

How do we prevent it to begin with?

To date, the only answers come from a Russian study,

an earthbound simulation of the approximately 520 days in isolation

it would take for a return trip to the Red Planet.

As the Russian study was gearing up, Dr Dinges set himself a challenge.

Could he use his expert knowledge to anticipate

who would fare best in confinement?

In the Mars 520 mission, I watched the crew intensively.

I wanted to see them during the maelstrom of media attention

before they went into the chamber and how they interacted

in that environment and body posture -

where they were looking, what they said.

I wrote down a variety of things. I made predictions,

and this is true - I sealed it up in an envelope and put it

in the drawer and waited till the mission was over.

In this footage,

released by the European Space Agency, the astronauts look well.

But by the end, deep troubles were brewing.

The bottom line is that, out of six people who went,

only two didn't have significant behavioural problems

of one kind or another.

A couple of them experienced insomnia.

One experienced some depression.

Um, another was more socially isolated.

But the two I predicted would make it just fine, made it just fine.

It seems that all the problems of putting astronauts on Mars

return to one thing - the mission's delicate payload of human beings.

And even if they survive the perils of the journey,

the most dangerous 15 minutes of the trip would still be ahead.

After nine months of psychological and physical discomfort,

the final few minutes of the journey to Mars

present some of the biggest challenges.

The first is communication.

Earth and Mars are both in orbit around the sun,

and so the time delay between them when we're at our closest, when

we're at the same points in our orbit, is only about four minutes.

But if we're on one side of the sun and Mars is on the other side

of the sun, that can be as much as 24 minutes one-way,

which means that if mission control are sending a message

to the astronauts, it can take 48 minutes for the answer to come back.

And that just completely changes how your astronauts are supported

by your teams on the ground.

When we went to the moon,

there was a delay of about a second or two in the communication.

The crew had to fire their engines

to go into lunar orbit behind the moon,

and all mission control can do is say, "Your computers are loaded.

"Good luck. We'll see you on the other side."

And what will happen with Mars will be like that, but a hundredfold.

The challenges of communication might make landing on Mars tricky.

But for Kevin, there's a far bigger problem,

and that's the Red Planet's thin atmosphere.

The Martian atmosphere is the worst of all worlds when it comes to

stopping in space exploration.

It's too thick to let you through safely,

but it's too thin to provide you with enough deceleration

to get you down to a useful speed.

It's not like landing on the moon. It's not like re-entry on Earth.

It requires a lot of novel solutions.

And we've seen some of that in our history

of robotic exploration of that planet.

The most audacious landing in the history of Martian exploration came

in 2012, when the Curiosity rover touched down in Gale Crater.

It was a cosmic ballet choreographed by Nasa engineer Dr Adam Steltzner.

Landing Curiosity, a tonne -

the biggest thing we've landed on Mars to date.

A challenge, but not nearly as much of a challenge as landing humans.

Humans are sensitive, they're delicate.

They don't like a lot of Gs.

They like to carry water with them.

They're heavy.

So we think that landing humans might be something

like 40 metric tonnes, or maybe more.

Once again, for the spacecraft carrying humans,

it's the bigger size that raises challenges.

There's this interesting pit of physics that occurs

as you scale up things.

Imagine scaling up a drop of water.

As it gets small or big,

its weight goes up with the size of it...

..cubed, raised to the third power.

But its aerodynamic drag gets larger based on its area,

which is its diameter squared.

What that means is the bigger the self-similar thing gets,

the more easily it falls.

The same thing happens with spacecraft.

So if you think about Curiosity,

she came in going very, very fast, slowing down,

slowing down and eventually making contact with the surface.

The smaller size of Curiosity meant that it was successfully slowed

by aerodynamic drag as it fell.

But scaling up the size for a human lander

changes the physics of landing radically.

I've got this self-similar shape.

I'm not going to not put Curiosity on the surface,

but I'm going to put TWO Curiosities, OK, three, four, five.

Getting a little challenging.

40. Now all of a sudden, I can't fly that shape.

It's the same shape it was before.

It's packed at the same densities of spacecraft,

but now it ends up flying a trajectory

that intersects the surface of Mars when it's moving Mach 20.

Not good.

Perhaps to get really big things to the surface of Mars,

what we need to do is...

We need to make our shape like this, which regular rockets look like,

but when we come flying in, we don't put the pointy end in

or the back end in - we come in sideways.

By coming in sideways,

the drag on the spacecraft is increased significantly,

slowing the rocket from hypersonic to supersonic.

To slow it down further,

you need something else to push against the gravity of Mars.

It's called supersonic retro-propulsion.

Imagine motorbiking with your mouth open at 60mph.

Waah! It fills your mouth with air

and it's actually sometimes hard to breathe out against it.

Well, that is the challenge of supersonic retro-propulsion.

You can light a rocket off into the flow,

but it's going to be supersonic flow.

Well, Nasa's working on that.

And it's likely to take those rockets from a supersonic condition

all the way down to the surface.

If Dr Stelzner's idea is developed,

it would pave the way for astronauts to land on the Martian surface

for the first time.

But even if they arrive safely,

they will face an immediate and potentially deadly challenge.

One of the most difficult things for those of us who imagine what it's

going to be like for a human crew

arriving at Mars is what shape they're going to be in

and how they're going to look after themselves,

because they're going to arrive after six, maybe nine months

of flight with all the deconditioning of their bodies

that we know is going to have happened.

And they're not going to be met by a huge army of medical professionals

and scientists who can then scoop them into

a state-of-the-art hospital.

Helen Sharman spent only eight days in space during her mission

to the Mir space station in 1991.

But she was completely reliant on the welcoming committee waiting

for her on landing.

Once we landed, the spacecraft was uprighted by the rescue crew.

The rescue crew pulled us out of the spacecraft,

glided us down a little sort of ramp into seats,

and then doctors came to monitor our blood pressure and other bodily

functions before they decided that we were fit and healthy.

There will be no such luxuries for astronauts landing on Mars.

They're going to be on their own and have to fend for themselves.

And so it is down to the crews who plan the missions,

down to the clinicians and the physicians who prepare them

to deliver them in as good medical condition as they possibly can.

If we can solve the challenges of landing safely on Mars,

it would set the stage for humans

to walk on the surface of another planet for the first time.

But what could WE achieve that robotic landers couldn't?

And how would we deal with the challenges of working on the surface

of another planet?

WIND WHISTLES

Over the last five decades,

robots have been our only way of exploring the surface of Mars.

They've been our cosmic emissaries,

gathering data and imagery for us to digest back on Earth.

But for Kevin, their limitations are too great.

For me, Mars is all about life,

and when you look at the history of our exploration

of early forms of life on this planet,

it was found in rocks by teams of geologists bashing on rocks and

examining them and coming up with thoughts

about where to explore next.

It was not and it could not have been found by parachuting something

that looked like R2-D2 into that territory.

That's the scale of the challenge,

and that's why you need humans in situ on Mars.

But if we get there, working on Mars will be no cakewalk.

Unlike Earth, Mars has no protective magnetic field.

So radiation continues to be an astronaut's biggest enemy.

Wild variations in temperature,

from minus 150 degrees in winter to 20 degrees in summer,

are another potential killer.

And with this comes another risk...

Powerful dust storms which can shroud the entire planet.

So for astronauts to live and work comfortably on the Martian surface,

they're going to need a new form of protection.

And scientists working on the next generation of spacesuits are taking

inspiration from a notorious incident

during the Apollo 16 mission.

Whilst walking on the lunar surface,

astronaut Charlie Duke dropped his hammer.

But the restrictive nature of his spacesuit meant

he couldn't pick it up.

He has real trouble retrieving the hammer.

So he just resorts basically to falling on it.

You can see we've progressed quite a ways.

So our crew members now, and our subjects now can now do a lot

of those functional, realistic tasks that you need to do

in a much more normal fashion that didn't scare spacesuit engineers

like Charlie did on Apollo.

Remarkably, spacesuits have changed little since the Apollo days.

And those worn on the Space Station are just as bulky.

So scientists are looking to slim down and add flexibility

in any way they can.

This suit was built so it can allow a flexing extension joint,

a waist bearing, and allows him a pretty wide range of motion,

very natural.

And you move your waist a lot when you walk and you don't realise that,

so that's an important joint to have.

And then we can watch him squat.

Touch the ground.

Seemingly small developments like this

take us closer to the prospect of sending humans to Mars.

You can see the joints work as he's doing these functional tasks.

If we can get working conditions for Martian astronauts right,

the scientific rewards would be huge.

Today, Martian science can only be conducted remotely by vehicles that

slowly trundle around the surface, gathering data and imagery.

For Curiosity mission planner and geologist Professor Sanjeev Gupta,

it's just no match for what a human scientist could do.

As a scientist working on the Curiosity mission,

the biggest challenge we have is how to pick where to go in the time

period we have to work.

Robots are simply not very efficient and they can't get everywhere.

When we command Curiosity, the tasks it conducts

in maybe a couple of days,

I could probably do in a few minutes by myself if I was there.

That time-saving element is crucial.

With Curiosity now, we skim at the surface of the science we can do.

We can do a bit of it,

but a human could just do it so much better and so much faster.

But for Kevin, it's not a choice between machines and humans -

it's about both working together.

The Pathfinder rovers took many years

to cover just a few kilometres.

The distance they covered in three or four years of exploration was the

same as that distance covered in a single afternoon

by the Apollo 15 lunar rover.

So you can see there how much more rapidly you can take on

an environment with human explorers

partnering with machinery than you can with robots on their own.

Helen Sharman prefers to concentrate on something else,

and that's giving astronauts like her the ability to think and act

for themselves.

Robots are totally reliant on the plans that were made

leading up to the launch.

So pretty much, the robot will do what you planned it to do

years before it got sent, whereas humans can do new things.

Humans can also take a look around.

And, "Actually, there's a bit of black earth over there

"or a bit of white rock over there.

"And although we'd only intended getting samples from this area,

"to get a good representative sample,

"we need to take a bit of black and white as well, thank you very much."

So humans can make those decisions.

The prize of putting humans in a position to do meaningful science

on the surface of Mars would be huge.

Our understanding of our nearest neighbour would be transformed

even with only a few short hours on its surface.

And there's one question in particular

that we are desperate to answer,

one that has consumed our thoughts more than any other.

-Gentlemen.

-The idea of astronauts stepping out of their capsule

and being greeted by little green men may be a hangover

from 1950s B-movies...

Are you here?

..but the question of whether there is or WAS life on Mars is creeping

towards a meaningful answer.

This is a location for great joy and peace on the planet.

Here's the thing. If it IS there,

it means that when you look up at the night sky,

it is a universe teeming with life, it's a jungle up there.

If you go to Mars and you find not only is there not any life there

now, but there never has been and it's a sterile planet,

then when you look at the night sky, it's a desert.

Many scientists put the odds at better than 50-50,

and landing astronauts on the surface of the Red Planet

should finally provide concrete evidence one way or another.

I don't know what the answer

to the question "is there life on Mars?" is. That's why we have to go.

As a scientist, I think it would be highly surprising

that life only arose on Earth.

I find that quite an incredible concept.

The biggest barrier to the existence of life on Mars

is the presence of water.

On Earth, all life is based on water.

It's the main constituent of every cell,

and it's thought that water is an essential ingredient for life

anywhere in the universe.

It's been known for almost a century that there are icecaps

at the Martian poles.

But with temperatures of minus 150 degrees,

these aren't good places to search for life.

What you need is liquid water.

And the first hint of that on Mars came in the mid-1970s.

These photographs taken by the Viking space probe in 1976

showed what looked like dried-up river valleys.

You can see one here.

You can see there's a valley through here.

You can see it branches.

There are tributaries.

Here's one branch going off here with tributaries.

So this looks very much like a terrestrial river system.

If these WERE dried-up riverbeds,

it meant that Mars must once have had the perfect conditions for life.

For Mars to have rivers, it must once have had streams, rain,

clouds and an atmosphere.

But for 20 years, they couldn't be sure.

The answers would come in 1998,

with the launch of the Mars Global Surveyor.

Sections of the valleys were revealed in fantastic detail.

Then, after they'd searched through thousands of images,

they found this.

A winding valley 2km wide and, at a bend in the canyon,

a tiny channel - the unmistakable trace of an ancient river.

In 2015 came confirmation of something even more remarkable.

Images sent back by the Mars Reconnaissance Orbiter showed

dark streaks that seemed to follow the contours of the landscape.

These streaks of moisture and salt

were incontrovertible proof that liquid water

still flows on the surface of Mars.

Follow that water, perhaps as it flows underground,

and maybe we'll find life.

If life is on Mars, it's most likely deep within the planet,

and that means having to dig down,

tunnel down very considerable distances. Many metres, if not more.

And that requires an effort

that isn't really doable by robotic platforms on their own.

You need human infrastructures.

But sending human life to Mars to hunt for alien life

presents another problem.

It's a bit of a paradox, actually.

If you want to discover life on Mars

or answer the question "is there life on Mars?",

sending life to Mars to try and discover that

might put Mars at risk.

The question of planetary protection -

protecting both Mars and Earth from cross-contamination -

is a central part of 21st century mission planning,

so much so, it's even enshrined in law.

Because Mars could still have life,

there are very strict UN rules on going and protecting the planet.

You need to make sure that you don't disturb any life on Mars

or introduce anything to it.

You need to make sure that if you were to bring anything back

to Earth, we don't put life on Earth at risk.

If we cannot promise to protect Mars, then maybe we shouldn't go.

But Kevin disagrees.

He thinks planetary protection is something we've already solved

with our experience closer to home.

We have had to think about that here on Earth, when we drilled recently

in Antarctica. There were efforts to drill many, many metres through ice

to ancient lakes that had been sealed off from the rest

of the world for over a million years.

And those protection issues,

protecting one system from another, had to be broached then.

So it's not like we don't have some quite mature thinking in this.

And this isn't an insurmountable problem.

Assuming we can solve the contamination issue

and do meaningful science,

the next question that will arise is even more challenging

than the journey to Mars.

When the Apollo astronauts returned to Earth,

it was to a heroes' welcome.

But for the astronauts going to Mars,

there's rather more uncertainty about their homecoming,

and that's because coming back from Mars will be just as challenging

as getting there.

Nasa and SpaceX are investing significant research

into the problem.

In particular, how to carry enough fuel for a return journey,

or even to mine it from deep under the Martian surface.

But the Dutch Mars One project scheduled for 2032

has a starkly simple solution to this conundrum.

Their astronauts will stay on Mars,

and never come home.

There are organisations out there

who are promoting the idea of a one-way trip.

There is an enormous amount of public interest in those

and, for me, it's fascinating to see the range of people

who are willing to go on such a trip.

But the idea of sending astronauts to their certain eventual death

poses serious moral questions

and has led to harsh criticism from across the space flight community.

I think any mission that only sends people one way

is just morally indefensible.

Even though the individuals might themselves accept

that they're only going to go one way,

it's just not right morally.

But for Kevin, the idea of a one-way journey to Mars

isn't so controversial.

It's just the latest in a long tradition

of risky frontier expeditions

in which coming home isn't guaranteed.

When you look at human history and the history of exploration of THIS

planet, people did often undertake very long journeys that were more

hazardous in many ways than the proposed trips to Mars,

that were going to be one-way.

If you were around 100 years ago and you saw Scott and Amundsen race to

the Pole and you watched the news come in of Scott's team perishing,

you must have thought, "For what? For what value?"

And yet, by the end of that same century,

the ice cores we were pulling out of Antarctica,

the paleoatmosphere that we were pulling out of the bubbles

in those ice cores, was giving us the most convincing

evidence yet that our climate was

warming at a rate never before seen in history.

And so, what started out as a meaningless adventure

that no-one could understand, by the end of the same century,

became knowledge that was literally the key to saving the planet.

There's no reason to expect that that might not happen on Mars.

Permanent settlement of Antarctica would have seemed like a pipe dream

to Scott and Amundsen.

Yet in the space of 100 years,

we've made this inhospitable corner of the Earth a place

where we can live and work safely for long periods.

Could we do the same on Mars -

make it a place not just to visit,

but somewhere to call home?

Mars!

Permanent human habitation on a planetary body other than the Earth

is one of science fiction's most prevalent themes.

TRANSLATION:

The relatively kind surface conditions on Mars

and the presence of water

make it the only place in the solar system other than Earth

we could even consider doing it.

The ultimate goal is to terraform Mars -

to transform its atmosphere and surface into a second Earth

that could support terrestrial life.

But it's a distant dream.

The romantic in me loves the idea of going to Mars

and terraforming it and greening it and colonising it eventually,

because it's testament to technological progress

that would mean that we had moved

beyond the so-called cradle of Earth.

Terraforming Mars may remain the stuff of science fiction,

but alternative ways to sustain life

are being given serious consideration.

These images, released at the beginning of 2017,

shown Nasa's concept for how it might be done.

These futuristic domes are built from an unexpected material - ice.

With water now thought to be in plentiful supply and water molecules

offering excellent protection from harmful cosmic rays,

maybe the first long-term settlers

will live in the Martian equivalent of igloos.

I can see that happening.

I can see us developing technologies that allow us to persist on Mars

for much longer periods of time than we imagine at the moment,

without having to go through the rigmarole

of terraforming the atmosphere.

We may reach that point that we may do that,

but it will take a fairly enormous effort.

To some, the question of a permanent settlement

on the Red Planet has more urgency.

As we continue to deplete the resources

and alter the delicate balance of Earth, many people argue

that we will need to settle on Mars as an escape route

from our dying planet.

Ultimately, the Earth will not be habitable. Whether or not we...

..we mess it up, it will not be habitable at some point.

And long-term, if we want humans to be able to continue,

we do have to learn to survive elsewhere,

but not at the detriment of our own planet.

At some level or another,

it has to be morally reprehensible

to be a species whose behaviour is that it trashes one planet

and then moves along to another one and then trashes that one.

That's not the way we should be.

That's not what we should strive for. We should look after

the very precious jewel that is our Planet Earth

and we should explore Mars responsibly.

Um, there may come a time when, inevitably, we have to move planet,

but that's, I think, much further in the future.

Whatever form our long-term relationship with Mars takes,

several things are clear.

Going to Mars will be astronomically expensive,

incredibly dangerous and highly controversial.

Can the benefits really outweigh the vast costs?

Or would we be better spending that money on something else?

I think in some quarters of the public,

there's this temptation to think that when you send people and things

into space, you load the payload bays

and you cram in these dollar bills and then you shut

the payload bay doors, and as it launches,

you sort of spread that money out into space

and it burns up on re-entry. Of course, that's not what happens.

Money casts a dark shadow over our hopes of going to the Red Planet.

Just landing a robot on a comet

for the Rosetta mission cost 1.5 billion.

But that's nothing compared to the expected 100 billion cost

of a mission to Mars.

In a world of fiscal austerity,

surely this money could be better spent?

Helen Sharman disagrees.

For her, the only way human space research

can continue to attract funding is to tell people compelling

human stories, and that means sending people.

It's often been said that you'll have two to three orders

of magnitude more value from a human mission

than you will from a robotic mission,

although a human mission will only be

one to two orders of magnitude more costly.

So actually, the value of humans on Mars is so much better

than the value of robots and rovers on Mars.

Humans relate to other humans.

So when humans go places and talk about what it's like there,

the rest of the world realises that actually,

there really IS benefit in us exploring further

something about that particular place.

Our exploration of the moon, with its six landings, cost 25 billion.

And its value has been the subject of endless debate.

To some, it was a colossally expensive vanity project.

But to others, the benefits were wide-ranging.

Many of the technologies we use today

were originally developed for Apollo.

We also learned a huge amount about the moon -

a legacy that continues today.

The third of a tonne of moon rock we brought back to Earth will keep

scientists busy for decades to come.

Those samples are still yielding new science results -

and major new science results -

changing our understanding of the evolution of the moon.

And, so, that legacy is just win-win-win continuously.

Who knows what a mission to the Red Planet will teach us about Mars...

about Earth...

and even about ourselves?

For Kevin, the question of money is secondary to a much bigger idea,

and that's the importance of exploration itself.

For him, without exploration of destinations like Mars,

we simply might not survive as a species.

The future of our species does depend in a very fundamental way

on exploration. It always has. It's what we've always done.

I think if we cease in our exploration now,

we are calling a halt to us as...

as a species that persists indefinitely.

You have to explore.

You know, it's a truism that to explore, you have to survive,

but the opposite is also true - that to survive, you have to explore.

The necessity of exploration, to go to Mars and beyond,

is a sentiment shared by some of the planet's greatest thinkers.

If the human race is to continue for another million years,

we will have to boldly go where no-one has gone before.

Spreading out into space will have an even greater effect.

It will completely change the future of the human race

and maybe determine whether we have any future at all.

We could have a base on the moon within 30 years,

reach Mars in 50 years,

and explore the moons of the outer planets in 200 years.

The idea of putting human astronauts on Mars is no longer an idealistic

dream, but one that may finally be on the verge of becoming a reality.

If we succeed,

it will be the most perilous and expensive journey

humans have ever made.

We're already well on the way to overcoming

the key technical obstacles to getting there safely,

but whether the cost and risk to human life are worth it

will continue to spark lively debate.

There's a lovely quote from Arthur C Clarke, where he says that we could

stop in these endeavours,

but to do so would be to turn your back

on billions of years of progress,

millions of years of human evolution

and to have begun to descend what he calls

"the slopes that end at the shores of the primordial sea."

And I think that's true.