Why doesn't Mars have an electromagnetic field?

[Cosmologist]

Why doesn't Mars have an electromagnetic field?

[Noclevername]

When Mars began to cool down billions of years ago, it lost its magnetosphere generated by the churning of internal fluids and was left with only residual magnetism. Mars' core is iron sulfide, which does not hold magnetism as strongly as nickel-iron.

[TrAI]

It seems that once Mars had a global magnetic field, but that was lost over 4 gigayears ago. The exact cause of its collapse is somewhat uncertain. From what I have read, the more common suggestions are that the internal heat dropped below the level needed to keep the dynamo effect going or that it was disrupted by one or a series of large meteoric impacts, or possibly a combination.

[cjameshuff]

It seems that once Mars had a global magnetic field, but that was lost over 4 gigayears ago. The exact cause of its collapse is somewhat uncertain. From what I have read, the more common suggestions are that the internal heat dropped below the level needed to keep the dynamo effect going or that it was disrupted by one or a series of large meteoric impacts, or possibly a combination.

I've never heard the latter suggested, and it seems quite improbable. The core is a big mass of iron, and is underneath a very thick blanket of stone. You'd need an impact by another small planet to disrupt the core, and the likely result would be heating the core up and extending the period it can generate a magnetic field for.

[SRH]

Just a few (dumb) questions...

Is it possible that Mars has a magnetic field, but it is so weak that it is just not detectable at the planet's surface or at a greater altitude/distance (i.e. it may be detectable at say the mantle region of Mars)?

Do all planets that have magnetic field also have a type of atmosphere?

Is there any correlation between a planet's magnetic field strength and its rotation speed?

Thanks.

[willstaruss22]

I was thinking if mars had more iron thus it was denser the maybe that would warm the core up enough to where it would melt because the pressures are higher. Mars isnt as dense as an earth type planet for the heavy light element raitio as earth so it is lighter thus less dense than it could be. That extra density would produce more mass thus more gravity and maybe enough to hold onto a thicker atmosphere as well as a stronger magnetic field.

[cjameshuff]

Is it possible that Mars has a magnetic field, but it is so weak that it is just not detectable at the planet's surface or at a greater altitude/distance (i.e. it may be detectable at say the mantle region of Mars)?

It doesn't have a global, structured magnetic field, but it does have a magnetic field...a weak, disorganized, chaotic one consisting of remnant magnetization in rocks that formed when it did have a global, strong magnetic field.

Do all planets that have magnetic field also have a type of atmosphere?

No. The moon has weak local magnetic fields (though no organized global field), and Mercury has a global magnetic field, though one that's much weaker than Earth's.

Is there any correlation between a planet's magnetic field strength and its rotation speed?

We don't really have enough of a sample to say from observation...there's only a handful of planets we can get a good look at. I'm not sure what the models predict, but it seems likely that higher rotation would allow stronger convection currents before the overall organized flows break down into a disorganized mess that can't generate a global field, so low rotation rate could place a limit on how strong the field could get, but high rotation doesn't necessarily mean a strong field.

[TrAI]

I've never heard the latter suggested, and it seems quite improbable. The core is a big mass of iron, and is underneath a very thick blanket of stone. You'd need an impact by another small planet to disrupt the core, and the likely result would be heating the core up and extending the period it can generate a magnetic field for.

Mars carry several very large(relative to the planet's size) impact craters from the period. The suggestion is, If I recall correctly, that the first impacts disrupted the convection flow patterns in the outer core and mantle so that there were no-longer a uniform magnetic field, and later impacts prevented the flows from re-stabilizing. If you Google mars magnetic field impact, you will find articles on the subject.

[publiusr]

Hellas alone is pretty big at 1,400 mi.