“The Earth destroys its fools, but the intelligent destroy the Earth.”
-Khalid ibn al-Walid
Usually, when we talk about terraforming, we think about taking a presently uninhabitable planet and making it suitable for terrestrial life. This means taking a world without an oxygen-rich atmosphere, with watery oceans, and without the means to sustain them, and to transform it into an Earth-like world.
The obvious choice, when it comes to our Solar System, is Mars.
The red planet, after all, is not a total stranger to these conditions. On the contrary, for the first billion-and-a-half years of our Solar System, give or take, Mars was perhaps not so dissimilar to Earth. With evidence that there was once liquid water on the surface, a thicker atmosphere, and possibly even life, there’s no doubt that the right type of geo-engineering could bring those conditions back.
But there’s also no doubt that we couldn’t, if we were sufficiently motivated, turn the Earth from this…
into a world where the atmosphere and the oceans were stripped away. Into a dry, nearly airless world, much like Mars.
Inspired by a recent Astronomy Picture of the Day, above, it’s now time to tell you how I would, scientifically, remove the oceans from the planet. It’s a process I like to call reverse terraforming, whereby you turn a world the Earth into a world like Mars.
At present, this is difficult for a number of reasons, but here’s the biggest one.
The Earth’s magnetosphere! The same reason that your compass needle points towards the magnetic poles of Earth is the only thing keeping our oceans here on our world! The Sun is constantly shooting out a stream of high-energy ions, known as the solar wind, at speeds of about 1,000,000 miles-per-hour (1,600,000 km/hr).
As the solar wind runs into a world, these ions collide with particles in a planet’s atmosphere, giving those molecules enough kinetic energy to escape from the planet’s gravitational field.
Of course, we have a powerful magnetic shield from the solar wind thanks to our hot, dense and (partially) molten core. Our planet’s magnetic field successfully bends away practically all of the solar wind particles that would be in danger of colliding with us, with the occasional exception of the polar regions, where the ions — and hence sometimes aurorae — get through.
Right now, our atmosphere is pretty thick: it consists of some 5,300,000,000,000,000 tonnes of material, creating the atmospheric pressure that we feel down here at the surface. There’s so much pressure, in fact, that our Earth can sustain liquid water on the surface.
The ability to have liquid water is relatively rare: we need the proper temperatures and the proper pressures! That means we need at least at atmosphere of a certain thickness, a characteristic that Mars, Mercury, and the Moon totally lack. But we’ve got it, and hence we can have liquid water on our surface.
And do we ever! There’s much more water than there is atmosphere. About 250 times as much, by mass, is the amount that the oceans outweigh the atmosphere, meaning that the oceans comprise about 0.023% of the Earth’s total mass!
But we could get rid of all that liquid water, eventually, by letting the solar wind in.
When the Earth and Sun’s magnetic field align, something like 20 times as many particles as normal make it through. Charged particles are bent by magnetic fields in very predictable ways, and if we could control those fields, we could control how much of the solar wind made it through.
In other words, if we could create a large enough magnetic field on Earth, we could poke a hole in the magnetosphere and allow the solar wind to strip our atmosphere away!
Something similar happened to Mars about 3 billion years ago, when its core stopped producing that powerful magnetosphere shield, and its atmosphere got stripped away. When the pressure at the surface dropped below a certain level, the liquid oceans there could only exist as frozen ice or boiled off as water vapor. (And once they’re water vapor, they become part of the atmosphere, where it, too, can be stripped away by the solar wind!)
It may not be fast enough for the most supervillainous among you, but one thing’s for sure.
If we do poke a hole in the magnetosphere and allow the solar wind in, I’ll definitely be enjoying the auroral show!