Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asked at the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and add free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

We have long dreamed of making Mars live again, and for that, you will need a magnetosphere

to keep a seas in sky, but could a few well-placed nukes really restarted spin?

The dream of a living Mars, just a couple days ago we talked about whether humanity should go to Mars,

and if so, when and why. Like me, such questions, the answer depends as much on our values and priorities as in our technology.

We could imagine countless futures, but each depends on the tools and ambition we bring with us.

What we didn't dwell on then, though it's a favorite topic of ours here, is the idea of

terraforming Mars.

Of all the worlds in our solar system, only Mars and Venus seemed to offer even a glimmer

of hope, but turning a dead planet into a living one.

For as long as we've looked up at the red dot in the sky, people have dreamed of making it

blue and green again.

In science fiction, Mars is humanity's second home.

A world we could warm, water, and teach to breathe, with enough will and ingenuity.

Yet behind every vision of a living Mars lies one stubborn obstacle, the planet no longer

has a magnetic field.

Without that protective shield, the solar wind longer has a magnetic field.

Without that protective shield, the solar wind has spent billions of years stripping

Mars's atmosphere, molecule by molecule.

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