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[♪ INTRO]

As much as space inspires us to imagine and explore,

it doesn't exactly welcome that exploration.

You've got deadly radiation, extreme cold, lack of oxygen, and those are just the start.

Some of the most tempting destinations in our solar system

are home to the most hostile environments you can imagine.

But Earth also has its fair share of hostile places.

And we can use them to prepare space probes and even astronauts

for some of the most unwelcoming places in our solar system.

And that includes our nearest neighbor, the Moon.

Even though it's the one other world humans have walked on,

the idea of something like a lunar colony is still a major challenge.

Any long-term explorers would need protection from radiation and the constant shower of micrometeorites,

because unlike on Earth, there's no atmosphere to burn them up.

But the Moon itself might have the perfect hideaway.

Back in 2012, NASA's GRAIL spacecraft created a high-resolution map of the moon's gravity,

which reflected differences in density under the surface.

The map revealed huge underground voids on the near side of the moon.

They seemed to be in shape of tunnels, some of them dozens of kilometers long and hundreds of meters wide.

Astronomers think these voids are massive lava tubes.

Lava tubes can form when cool air solidifies the outer layer of a lava flow.

When the molten rock inside drains away, it forms a natural tunnel.

And these giant lunar lava tubes could be the perfect refuge for humans.

Not only could they house a whole city, they could provide shelter from radiation, micrometeorites,

and the Moon's extreme temperatures.

So, scientists like those at JAXA, the Japan Aerospace Exploration Agency,

are considering building our first lunar cities inside lava tubes.

It's a pretty dramatic idea, but fortunately, we can do a practice run.

Here at home, we also have lava tubes in volcanically active places

like Hawai'i, Iceland, and the Canary Islands.

The tubes are smaller because Earth's stronger gravity collapses any that get too big,

but they still make a pretty great laboratory.

In Lanzarote, one of the Canary Islands, lava tubes stretch more than 8 kilometers in length.

They go from openings in the surface to more than 50 meters below sea level.

And inside, the European Space Agency has been training future astronauts and mission specialists since 2016.

The trainees work alongside robots inside these volcanic caverns,

and practice using pioneering technology to do things like map the cave systems

and look for signs of water and life.

These are techniques that will keep them alive and help them scope out the alien environments

they might one day encounter on the Moon.

As barren as it is, the volcanic landscape of Lanzarote is charming

compared to some of the more hostile environments in the solar system, like Mars.

Even though it's our most-visited planet,

we still struggle to answer the one basic question that keeps drawing us back:

Has it ever had life?

Mars's surface is unbelievably dry and cold,

and its thin atmosphere means that its soil can't catch a break from radiation.

So if it has life at all, it's probably microscopic and buried beneath the surface for protection.

And NASA is developing a rover that they hope will be able to detect life like this.

And luckily we have just the place on Earth to test it out.

The Atacama Desert in Chile is one of the driest places on Earth.

Some areas get just 1 to 3 millimeters of rain a year.

Between this and the chemical makeup of its soil,

it's about as close to a Martian environment as you can get on our muggy planet.

The microscopic Atacaman life is forced to live underground,

where the last drops of water might persist.

Now, scientists are using a rover to look for these buried microbes, just like we would on Mars.

The Atacama Rover Astrobiology Drilling Studies project, or ARADS,

has designed a rover that can drill down as much as 2 meters, through soil, salt, and rock,

and return samples to its onboard lab.

NASA hopes to be able to detect signs of life from these samples,

and this test run will tell us if a rover like this could pull off the same stunt on Mars.

Much deeper in the solar system, scientists are eyeing Jupiter's icy moon Europa

as another target for robotic explorers.

Astronomers believe the moon has a liquid ocean, and, as far as we can tell,

liquid water is the number-one requirement for life.

The thing is, that water and any life it contains are buried beneath a 20 kilometer-thick crust of ice.

Which is kind of inconvenient, but maybe not impossible.

Right now, scientists are training robots using our own ice-covered ocean, the Antarctic.

A team at Georgia Tech has developed a long-range, underwater rover called Icefin.

It's about 3.5 meters long but just 23 centimetres wide,

which lets it slide into narrow boreholes that the scientists drilled in the ice.

This robotic explorer can then dive beneath the Antarctic ice shelf and navigate on its own,

all the while surviving freezing temperatures, crushing pressure, and unpredictable currents.

But it can do much more than just survive.

Instruments onboard Icefin can take high-resolution measurements of the environment.

And that's exactly what we'll need any Europan explorer to do,

if we want to get a picture of this alien ocean and figure out if it's habitable, or even inhabited.

Of course it'll take more research before we're ready to launch an underwater drone

to an icy moon more than 600 million kilometers from home.

So Icefin itself won't make it to Europa.

But its great-grandchild might.

In the meantime, Icefin's measurements are helping us

understand and document the melting of Antarctic glaciers.

It turns out that in reaching for space,

we're also learning about some of the most amazing places on Earth.

And preparing for hostile worlds gives us even more reason to appreciate the one world in this solar system

that actually does welcome us.

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