Mars’ Missing Magnetosphere
If Mars was magnetic, could Life have lived?
Among the swirling clouds of cosmic dust, small lumps were slowly forming. Tiny particles happened to get together, and their combined gravity served to pull in even more. Soon — which is to say, in a few million years or so — much of the material had become a gigantic ball of fire, with several much smaller spheres travelling around it.
Two of those spheres were very special. They were just the right distance from the fire — not too warm and not too cold — to allow liquid water to form. Water, it is believed, is essential for life as we know it. Combined with the rich minerals on the early spheres, it would make the perfect conditions for life to arise.
And that’s just what happened.
Life appeared in one of those places. It grew, it spread, and took over the whole world it lived on. And it gave its world a name, Planet Earth.
This is the story of the other planet.
In the past, Mars used to be a lot like Earth. It was smaller, it’s true, but it too had a day of about 24 hours, and thick atmosphere, and many of the minerals and elements that earthly life needs to survive. Several billion years ago, evidence suggests, Mars could have been so earthlike that, if you had been there and found a pool of water, you would have been able to drink it.
But then, Mars lost its magnetic field.
People don’t usually think much of their planet’s magnetic field. True, it makes their compasses point north, which is handy, and creates the auroras, which is nice — but it doesn’t seem to do anything absolutely essential for life.
Actually, it does.
Look at the Sun. No, wait, don’t. The light of the Sun is so bright, you could go blind just by looking at it. Just a few seconds too long, and you’ll never be able to see again.
The Sun is one gigantic powerhouse of energy, and a lot of that energy goes shooting out into space. What reaches the Earth is only one tiny part of it. And yet, even that is enough to keep the planet running. Whether it’s plants catching sunlight, or animals eating those plants, or even animals eating other animals, all the energy used by life ultimately comes from the Sun.
But it’s not just warmth and sunlight that comes from there. The sun also sends out “solar wind”: streams of fast-moving, electrically charged particles and radiation, that would be very bad for living creatures if it reached them.
Luckily, the particles are magnetic. That means, as they approach the Earth, the planet’s magnetic field deflects them away.
On Mars, the particles are able to hit the atmosphere directly. They can go tearing through the atmosphere, and carrying a large part of the air molecules along with them.
This is not a one-off thing. It happens every day, all the time. That’s why, over billions of years, Mars’ atmosphere has been slowly but steadily getting thinner, and escaping out into space.
And the atmosphere isn’t the only thing that goes.
Water, as I mentioned, is essential to life. And Mars has quite a lot of it.
Unfortunately, it’s frozen.
Mars has two ice-caps, one on each pole, just like Earth. The frozen water in the South Pole, if melted, would be enough to cover the whole planet to a depth of eleven metres. But that’ll probably never happen.
To have liquid water, it’s not enough to keep it at the right temperature. You also need pressure. Otherwise, the melting water won’t stay liquid; it’ll turn into gas and fly up, out and away. The reason it doesn’t do that on Earth is that there’s so much air on top, pressing it back down.
There are some places, down in the deepest valleys, where water can become liquid for a few minutes or hours. Those are the places that have the most atmosphere above them. More air, more pressure.
Air, it turns out, isn’t quite so thin after all.
Liquid or solid, pressed or not, there’s evidence that Mars once had much more water than it does today.
Water is a molecule. It’s made out of atoms. When an oxygen-atom joins with two hydrogen-atoms, they form a molecule of water. The evidence lies in the fact that there’s more than one kind of hydrogen.
The heart of an atom is made up of many smaller pieces, but they come in two varieties: protons and neutrons. It’s the protons that decide what kind of atom it is. Four protons means Carbon, three means Lithium, two mean Helium, and so on.
Hydrogen is a very simple atom: it has just one proton. But how many neutrons does it have? Usually, none at all. Sometimes , however, it does end up with one neutron . That’s what’s known as “deuterium”.
And when water is made with deuterium atoms, it’s called “heavy water” — because it is, well, heavier. (Neutrons don’t weigh nothing, you know).
On Mars, heavy water is more common than usual. Why could that be?
Make a guess.
Done? Now you can read on.
The gravity of Mars is not as strong as Earth’s. It can’t hold onto things as easily. And, with no strong magnetic field, there’s nothing stopping the solar wind from ripping everything away.
Everything, that is, including water vapour.
Do you see the answer now? A lot of the melting water evaporated and went out into space. But the “heavy water” was heavier, so it didn’t rise as easily. That’s why there’s more of it left!
And it’s not just water. Other gases, too, have more of their heavier editions than in other parts of the solar system.
But why did Mars lose its magnetic field at all? That’s what nobody knows. They’re not even sure why Earth has a magnetic field.
One theory for that is, there’s lots of liquid molten metal in the centre of the Earth. As the planet rotates, the metal moves more slowly, acting as a kind of dynamo to generate a magnetic field.
Mars has no molten dynamo, but there are signs that it did have one, over four billion years ago. Vast, rocky areas on the planet are magnetised in identical directions, as if they had been exposed to a very powerful magnet for a very long time. A magnet that, we’re guessing, covered the whole planet.
Even today, the effect is so strong that Mars does have a magnetic field of sorts — but only in the southern side.
In the south? Why only in the south? It’s likely that Mars’ internal dynamo once magnetised the whole of the planet’s surface. But then, something happened to de-magnetise the northern half.
Scientists suspect that something very large and heavy — like another planet, perhaps — collided with Mars at that time, banging it so hard on that the northern part lost its magnetism. That would also explain why the north of Mars is relatively smooth and flat, while the south is filled with cracks and crevasses, and mountains, and valleys.
The Northern Magnet wasn’t completely destroyed. Even today, there are many areas in the planet’s crust that hold on to their ancient magnetism. These “mini-magnetospheres” do, on a local level, what the magnetosphere used to do for the whole planet.
They keep the solar winds at bay, and help the atmosphere to stay.
While Planet Earth turned out to be just about right for life, Planet Mars turned out to be just about wrong. Mars had quite a few things going against it. With its weaker gravity, it may not have been able to hold its air, magnetosphere or not. And less air means less insulation, and no liquid water, and hotter days and colder nights and a temperature that keeps on switching.
But there is still some hope.
The most humid parts of Mars are about as wet as the Atacama Desert in Chile. Even if they can’t fined water, some of the microorganisms there are able to live off the wetness in the air.
It seems they still need water to reproduce and have children, but maybe they can do that in deep valleys under morning mist, when water forms in puddles for a few short hours. They can do it in sheltered places, protected by mini magnetospheres, which stop the sun’s charged particles from hitting the ground.
And what about under the ground, where no charged particles ever get through? That’s a different story….
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