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There’s been a lot of talk lately about sending humans to live on Mars. But it’s easy to say that and a lot harder to actually do it.

A big part of that is because Mars … isn’t especially friendly to human life. Or life at all. It’s freezing, with a super thin atmosphere that not only makes it impossible to breathe, but also doesn’t give you much protection from all the deadly radiation coming from space.

To change that, we’d have to terra-form Mars, changing its geology and climate to be more like Earth. Which is usually a subject more appropriate for sci-fi than science. But at the Planetary Science Vision 2050 Workshop in early 2017, a group of scientists led by the head of NASA’s Planetary Science Division suggested a way we might get started.

Their plan? Build a giant force field — a protective magnetic field — for the planet. And as weird and impossible as that sounds, it’s not totally science fiction.

The idea is that this magnetic field would replace the one Mars lost long ago, which would then let the planet build up a thicker atmosphere. Billions of years ago, Mars might have looked a lot like modern-day Earth, with a magnetic field, a warm atmosphere, and oceans on the surface with about as much water as our Arctic Ocean. But for reasons scientists still don’t fully understand, Mars lost its magnetic field about 4.2 billion years ago.

And everything kinda went downhill after that. Without a magnetic field to block the charged particles streaming from the Sun — aka the solar wind — much of the Martian atmosphere got stripped away over the course of about 500 million years. Without a thick atmosphere to trap heat, the planet froze and its oceans were lost forever.

Unless we can find a way to bring them back, that is. Even today, four billion years later and with barely any left, Mars can lose up to a kilogram of atmosphere to space every second. We’ll never get back all the stuff that’s escaped into space already, but there’s still gas leaking out of the planet’s crust, so there’s at least some hope of building it back up.

If we could, that would provide more protection against the radiation, plus help warm the planet a bit. Astronomers also think there might be enough water trapped in the polar ice caps to rebuild about a seventh of the ancient oceans, if we can get the climate warm enough for the ice to melt. But first we have to get the atmosphere back, and that’s where this NASA team’s big idea comes in.

If we could block the solar wind from stripping away the atmosphere, it might start to build back up again. At first, that might sound like it involves building something the size of a planet. And that’s … not super practical.

But the researchers proposed a way to get around the problem: by taking advantage of the fact that the solar wind is only coming from one direction — the Sun. So all we’d need to do is … block the Sun, kind of like what the Moon does during an eclipse. Which, yeah, would still require a huge shield, but we wouldn’t have to build a giant solid thing — it would just be a magnetic field.

And that might actually be practical someday. All we’d have to do is figure out how to generate the field. Then it would reach out into space and do the rest.

More specifically, the team suggested putting a field-generating device about a million kilometers from Mars. The magnetic field would have to be a bit stronger than the Earth’s, which would be hard on such a large scale, but it’s something we could probably figure out how to do. To understand what that would do to Mars, the researchers followed a two-step process.

First, they used computer simulations to calculate what a magnetic shield would do to the atmosphere. Then, they used climate models to predict what effects those changes would have. The results suggested that Mars’s climate would change a bit, but that we shouldn’t get our hopes up too much.

Although a strong enough field would stop the solar wind, that’s only one of the processes making Mars lose its atmosphere. The planet’s weak gravity and molecular interactions with sunlight also contribute. In a process called photo-ionization, atoms and molecules in the upper atmosphere can absorb energy from light and break apart.

Some of those pieces end up with enough energy to break free of Mars’s gravity and escape to space … which is not good if you’re trying to keep the atmosphere around! And although the global temperature would rise, this would mostly happen near the equator … which is not where the ice is. In fact, because of the way atmospheric physics works, it might even get colder at the poles than it is now.

That would keep all the dry ice, which is made up of solid carbon dioxide, trapped in the polar ice caps instead of vaporizing it into gas that would thicken the atmosphere. Plus, that dry ice is sitting on top of the water ice needed to refresh the global oceans. And even if the shield was enough to thicken the atmosphere and bring back the oceans, it would take a while.

Like, the researchers didn’t even have an estimate of how long. So I wouldn’t count on taking a boat down Valles Marineris anytime soon. But the idea is intriguing, because unlike many other terraforming ideas, the technology seems … pretty doable.

MRI machines use fields even stronger than what this research calls for; we just need to figure out how to make a field of the right shape and size. And get it into space. And the idea of putting something between the Sun and Mars isn’t that different from some proposals for dealing with climate change here on Earth.

For example, some scientists have suggested that one day we might be able to launch what would basically be a giant pair of sunglasses to block some of the Sun’s rays and cool the planet. But before we give Mars its very own Hylian shield, there’s another question that needs to be answered: even if we can do this, should we? There’s a lot we still don’t know about our planetary neighbor, and we still haven’t completely ruled out the possibility of alien life over there.

If there is life on Mars and we totally transformed the planet like this, we’d basically be destroying its habitat. But with no immediate plans to actually give Mars a magnetic shield, hopefully we have plenty of time to work those questions out. Thanks for watching this episode of SciShow Space!

If you’re interested in learning more about the hardest things about living on Mars, you can check out our episode about just that. [ ♪ Outro ♪ ].