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Are there ways to terraform Mars -- that is, make it habitable for humans? Some scientists think so. They have big plans, but they also face some big obstacles.
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Sources:
http://meteorite.unm.edu/site_media/pdf/BringingLife.pdf
http://science.nasa.gov/science-news/science-at-nasa/2001/ast09feb_1/
http://www.fromquarkstoquasars.com/terraforming-mars/
http://www.universetoday.com/9730/zubrin-on-terraforming-mars/
http://science.howstuffworks.com/terraforming.htm
http://www.pbs.org/exploringspace/mars/terraforming/no_flash.html
http://io9.com/5868115/how-we-will-terraform-mars
http://www.marssociety.org/home/press/news/howwewillterraformmars

*intro music*

In some ways, Mars kinda sounds like a cool place to live, doesn't it? The red soil, the craters, the dormant volcanoes - seems pretty scenic. And if you chose the right real estate, you could use one of the Viking landers as like, a lawn ornament or something.

But of course you'd have to be okay with temperatures around minus sixty, an unbreathable atmosphere, and deadly doses of radiation. Which for most people are kind of deal-breakers.

But technology can do some fantastic stuff, and scientists who study terraforming - the science of transforming a planet to support human life - have put a lot of thought into changing these things.

Turns out with a few centuries worth of effort, we might be able to make Mars habitable for humans. But I'm not gonna lie to you, it would be really, really hard. A whole bunch of major things would have to change.

Most importantly, Mars needs an Earth-like atmosphere. There are a few theories about how to create one, and they have a lot to do with the planet's history.

In its younger days, about four billion years ago, Mars was actually pretty similar to Earth. It was warm and wet, and had something of an atmosphere. That's because the Martian soil absorbed a lot of carbon dioxide and nitrogen that was floating around in the air, but then, active volcanoes recycled those materials by baking them out of the soil, so they could be absorbed - again.

The result of this was an atmosphere that mostly stayed put. Asteroids that kept hitting the planet helped out too - keeping it nice and warm. And back then, Mars had a magnetosphere, a planetary magnetic field that protected the atmosphere from being stripped away by solar winds.

But then the planet cooled, and lost its magnetosphere. There were fewer asteroid collisions and its volcanoes stopped erupting. Without all that help, Mars' surface absorbed a lot of the compounds from its atmosphere, and lost most of what was left to solar winds, leaving a freezing, dry, barren world.

Sounds pretty bleak, I know, but given what we know about Mars' history, with a little tweaking, we might be able to bring that atmosphere back. Basically, we need to start a massive global warming effect - something that humans seem pretty good at, and scientists have come up with three main ways to do it.

The first and the easiest way might be to just build factories that would basically turn carbon, fluorine, and sulfur in the Martian soil into greenhouse gases, and pump them into the atmosphere. This would unlock one of Mars' greatest assets when it comes to warming things up. The thick layer of dry ice, or frozen carbon dioxide that covers its south pole. An initial burst of greenhouse gases could cause this ice to sublime directly into vapor, releasing carbon dioxide gas that would help trap more heat from the sun, in turn releasing more greenhouse gases. But all that would take a while, and it would be tough to supply those factories with the resources they'd need.

So, another method might be to build giant two hundred kilometer wide mirrors in space. They would reflect sunlight onto the Martian ice caps, raising the surface temperature, and releasing that carbon dioxide.

If neither of those ideas worked, there's always the possibility of bombarding the planet with asteroids. In this scenario, we'd capture asteroids on the edge of the solar system, and use rocket engines to propel them into Mars. The ammonia in the asteroids would act as a greenhouse gas.

But each asteroid would be like a seventy thousand megaton hydrogen bomb, so aside from the obvious logistic problems, we'd have to do this way before humans were ready to set up shop there.
And even then, once the atmosphere had some greenhouse gases in place, it would still need an ozone layer - a shroud of molecular oxygen that would absorb some of the Sun's dangerous ultraviolet radiation. So there would have to be yet another step, where we introduce organisms like cyanobacteria or lichens, which would help enrich the soil and release oxygen that could eventually form ozone. Once the ozone layer was in place, the final ingredient for an Earth-like atmosphere could be added - nitrogen.

This could be introduced by asteroid bombardments, or bacteria could extract it from the nitrogen-bearing compounds locked in the regolith - the rock layer just above the Martian bedrock. Easy-peasy, mission accomplished, right? No - not quite. Mars would also need a way to hold onto its atmosphere, and keep it from being stripped away by solar winds.

Basically, it needs to get its magnetosphere back, which is the biggest problem with terraforming, because we really don't know how to do that yet. Earth has a magnetosphere which we're pretty sure is formed by liquid metals in the core that create an electro-magnetic field as they slosh around when the planet rotates. The same effect would happen on Mars, if we could only figure out how to melt its core, which appears to be solid metal, not liquid.

So if anyone has any suggestions on how to liquefy the middle of Mars, we're all ears. 

In the meantime, thanks for joining me for this episode of SciShow Space. If you wanna learn how you can help us keep exploring the universe together, go to subbable.com/scishow. And don't forget to go to youtube.com/scishowspace and subscribe. 

*outro music*