How the Universe Works - Eleventh Season

Our neighbor, Mars, fascinates us.

It's a planet that is similar to Earth,

but with some big differences.

Mars is rusty, dusty, frigid, and frozen.

It ain't the kind of place you want to raise your kids.

Past missions suggest that Mars

was once a very different world.

The Mars we see today has completely changed

from the Mars of a few billion years ago.

If I had a time machine to visit Mars

in the past, I would go in an instant.

Without a time machine to explore

ancient Mars, we employ a team of high-tech

robot investigators.

We've got an entire fleet

of robotic spacecraft exploring the planet.

Working together, they dig into Mars's past to answer

the ultimate question...

Did Mars once have life?

February 2021.

The newest robot investigator speeds towards Mars,

the most advanced rover NASA has ever sent to

another world.

This is Perseverance.

The goal of the Perseverance mission is

to look for signs of past life on Mars.

First, it must navigate safely

to the surface of the planet.

Every landing has its own dangers.

Because the rover must be autonomous,

it has to do everything without our help.

Perseverance enters Mars's thin atmosphere at

close to 12,500 miles an hour...

and deploys a parachute.

The parachute slows Perseverance

to 200 miles per hour.

Still too fast to land safely.

To prevent a violent impact,

the rover must activate the sky crane.

When I first saw the sky crane concept,

I thought, hm, the engineers are kind of losing it.

It seemed to me like a really crazy idea.

Perseverance activates its jetpack.

Retro rockets slow the lander's descent to a crawl.

Then, 66 feet above the surface,

the sky crane uses cables to

gently lower the rover to the ground.

Step one in the search for Martian life,

find evidence of liquid water.

A good place to start is the 28-mile-wide

Jezero Crater.

Perseverance has landed in a crater called Jezero, and this

looks like a place where there was liquid water in its past.

And the reason we think this is because

there's this beautiful delta deposit right in the middle.

Perseverance turns its high-resolution cameras

onto a cliff side in the crater

and discovers giant five-foot boulders near the top.

A clue to how they got there may

come from the first probes to visit Mars.

One of the very first things we noticed about Mars

when we first sent probes there

with Mariner and Viking was that there were these huge

channels on the surface of Mars.

Looking at these enormous landforms,

we realized that, in some places on Mars,

there may have been enormous floods,

bigger than almost anything we'd ever seen on Earth.

Flash floods on Earth cause similar rock formations to

those found in Jezero Crater, suggesting that powerful,

fast-moving torrents carried the giant rocks found by

Perseverance and dumped them at the top of the cliff.

Perseverance is just one member of an elite team

of robots patrolling the ground

and spying from the air.

The Mars Atmospheric and Volatile Evolution

Orbiter, or MAVEN, investigates Mars's atmosphere.

MAVEN smells really good.

It smells the Martian atmosphere.

It tells us what the Martian atmosphere

is made of all across the planet.

Then there's the MARS Reconnaissance Orbiter.

As its name suggests, an orbiting spacecraft

that images surface of MARS.

The M.R.O.'s high-resolution cameras

can identify surface features as small as a kitchen table.

And joining the orbital crew,

The European Space Agency's MARS Express.

With its ground-penetrating radar,

it searches for evidence of subsurface water.

And, on the Martian surface, a group of high-tech landers

take a closer look,

including the team's quake specialist, Insight.

This lander probes deep beneath the surface

to discover how Mars's interior shapes the planet over time.

The Insight lander on MARS has a really simple concept.

You land a spacecraft on the surface anywhere

on Mars and then just listen for Mars quakes.

And 300 miles south of Insight, veteran rover,

Curiosity is exploring the Gale Crater.

The mission goal for Curiosity is to look for habitability,

and so that's environments

in which life as we currently understand it could exist.

Curiosity searches for evidence of calmer,

more permanent water in Mars's past.

Investigating layers of rock at the base of Mount Sharp,

a three-mile-high mountain in the middle of the crater.

The rock layers start way up at the top of

Mount Sharp, and they move progressively downward,

and basically, we're going backwards in time until we get

to the very bottom, and the very bottom is actually really old.

Mount Sharp was built over millions of years,

layer by layer.

The rocks at the base of

the mountain date to 3.5 billion years ago.

These rocks are made up of very fine layers

and could only have been formed in calm water.

These sedimentary layers were formed when Gale Crater was

a lake, and sediment settles out, and you get these

beautiful layers.

Curiosity explores more of Gale Crater

and discovers rounded pebbles, like those we find on Earth.

When you see a rounded pebble on Earth,

you know that that got rounded in a river channel.

Some of them used to be angular,

but their angles all got knocked off by being rolled

and rounded and moved by water.

So we're very excited when we see rounded pebbles on Mars.

The rock layers and rounded pebbles

tell us that over three billion years ago,

Gale Crater was a lake fed by rivers.

It was so exciting to understand liquid

water in the context of Gale Crater,

where Curiosity is, and that's just because what we see there

is this long-lasting,

freshwater lake, and that's not like anything else

we've seen on Mars before.

Imagine standing on the edge

and looking out at this big, beautiful

blue lake shining in the distance.

What if there were just a whole array

of craters filled with water off in the distance?

It would be so beautiful.

And a good place for life to evolve.

Mars was a nice place.

It was probably more like Earth is now.

So it wouldn't surprise me if it's supported life.

We're talking microbial life.

We're not talking, you know, Marvin the Martian or anything

like that, but life still is life.

Any water Mars once had

is now long gone.

To stay liquid, water needs warmth

and atmospheric pressure.

So, hundreds of miles above the planet,

orbiting members of the team investigate the mystery of

Mars's missing atmosphere.

While robot team members,

Curiosity and Perseverance, work the Martian surface,

eight probes orbit the planet,

searching for clues about Mars's ancient wet history.

Leading the pack is MAVEN.

Its mission...

To solve the mystery of Mars's lost atmosphere.

Today, the atmosphere of Mars is incredibly thin.

It's only about 1 percent the atmospheric pressure

here on Earth.

The weight of gas in

an atmosphere pressing down creates pressure,

and that pressure dictates at what temperature liquids boil.

Here on Earth at sea level,

the boiling point of water is about 212 degrees Fahrenheit,

but up here in the mountains near Denver,

we're at a higher altitude.

We've got a lot less atmosphere pressing down on us,

and so it boils at a lower temperature.

Let's put a thermometer in here.

There's 200 even right there.

That's a lot cooler boiling temperature than at sea level.

Now, if you go to even higher altitudes at 100,000 feet

here on the Earth, the air pressure is about

what it is on the surface of Mars.

On the surface of Mars,

water will boil effectively at ambient temperature.

We wouldn't have to heat it at all.

You just put a glass of water on

the surface of Mars, and it'll boil and disappear away.

But the planet's surface tells us that dry Mars

was very different in the past.

When you see things like river channels

that probably took millions of years to carve,

that gives you an idea that the atmosphere was once very,

very different.

It had to be thick to allow

liquid water to exist on the surface.

To investigate what happened to that thick

Martian atmosphere,

MAVEN swings into action.

One of the main objectives of

the MAVEN mission was to measure argon on Mars.