NASA Proposes a Magnetic Shield To Protect Mars' Atmosphere (phys.org)

New submitter Baron_Yam writes: Apparently it is no longer necessarily science fiction to consider terraforming the red planet in a human lifetime. NASA scientists have proposed putting a magnetic shield at the Mars L1 Lagrange Point, diverting sufficient solar wind in hopes that the Martian atmosphere would thicken and heat the planet to the point of melting the ice caps, causing what remains of Martian water to pool on the surface. While not enough of a change to allow walking around without a space suit, this would make human exploration of the planet a much easier task.

Comments

No real information

[Anonymous Coward]

They don't mention much about how this magical magnetic barrier is going to be generated or powered. They also don't really know how long it will take a habitable atmosphere to form assuming it works at all, or what happens to everything if the shield fails at a later date and what kind of upkeep it would require. It sounds a lot like wishful thinking and hand-waving.

Re:No real information

[rgbatduke]

Well, that escalated quickly! Howbow I just reply to your first questions, because sunlight blocking isn't related nor makes much sense to me.

Let's try to make it make sense. The solar wind is driven by light pressure. Particles do not, however, follow strict radii out from the sun. They have transverse velocity components as well as radial ones. Also, they are pushed by photons from all over the face of the sun, which have different impact angles, which constantly change their transverse velocity. To put it another way, the particles driven away from the sun that will eventually hit Mars have a phase space envelope at least as large as the truncated cone formed by the surface of revolution whose boundaries are the circumference of the Sun on one end and the circumference of mars at the other.

Now consider a satellite (say) 100m in diameter. Suppose you locate it at the Lagrange point so that it is always along the line between the center of the Earth and the center of the Sun. Question: Will it dim the total sunlight received by the Earth?

Not measurably. The penumbra of this little satellite extends from its dark side to the tip of the extended cone formed by the circumference of the satellite and the circumference of the Sun. Since the Sun is basically 0.5 degrees from the Earth or the Lagrange point either way, the height of this cone is found from tan(0.5 degrees \approx 0.02 rad) \approx 0.02 rad = 100/H, or
50x100 = 5 km. So the satellite will cast a complete shadow of the sun that starts out 100 m wide right behind the satellite, then shrinks to zero around 5 km (give or take a km, I'm being lazy) . Beyond that you are in the umbra, which basically means that you are in bright sunlight from the annulus of sun surface visible around the satellite. The further out you go, the smaller the ratio of the occluded part to the directly visible part. By the time you reach the earth, the satellite is completely invisible -- the umbra is irrelevantly dimmed relative to no satellite at all, and it "covers" less of the sun's face from any viewpoint on Earth than a medium sized sunspot.

Now, if somebody were to tell you "hey, we're going to fix global warming by putting a sun shield in geosync orbit to reduce the total insolation of the Earth", your first concern would be to think about the geometry of that penumbral cone with a known cone height of roughly 5 earth radii vs a 0.5 degree Sun. Just how large would it have to be to reduce total insolation by a single whopping percent? The answer is really, really large. Even at only 5 Earth radii, which is not the distance to a Lagrange point. At the Lagrange point, really really REALLY REALLY large.

Now, is the solar wind deflection by a magnet going to be exactly like this? No, of course not. The magnetic field doesn't have a sharp cutoff -- it drops off roughly like 1/r^3 from the center of the (presumably dipole) magnet. Also, the force acting on the solar wind (charged only) particles depends on their charge and speed, the acceleration depends on their mass as well, and it has the usual nasty cross products in it so that it only really exerts a large force when particles run across the field at right angles. One would LIKE to think that a small deflection far away produced by a magnet large enough to produce a reasonable deflection a REALLY REALLY large distance away from the magnet could create a shadow as large as Mars, but it is by no means clear that this is the case, and just saying "hey, we can make really big magnets" doesn't actually help. I've got really really big magnets in my house -- ones I've pulled out of dead hard drives, that can basically hold a (small) newspaper pinned to your fridge. IF you get them within an appallingly short distance of the fridge. From a meter away, you can't feel any force at all. If you take an old CRT television or computer monitor and wave this really really strong magnet from ten or twenty meters away, it has

Re:While were at it

[KiloByte]

Well, a 22km (72,000 foot for those using medieval units) mountain is not high enough for you? Add water and you'll have snow.

Re:Actually doesn't sound all that nuts

[drinkypoo]

You'd think, for instance, somewhere someone should be experimenting with the minimum requirements for rendering Martian regolith into non-toxic, fertile ground.

You would think that, yeah. Indeed, we probably have some sort of simulated martian regolith that can be used for this sort of research.

Toying around with the power requirements to augment Martian sunlight and temperatures to levels required to support Terran plants or trying to engineer plants that will grow and thrive at Martian insolation levels.

That sounds quite handy.

Or playing around with in situ production of building materials, automated mining and refining equipment, etc.

Yes, it would be handy if you could make bricks, or perhaps concrete.

I'd certainly be up for a really inhumane experiment

When can you be ready to go?