[godson_drafty]

* an iron core that produces a magnetic field surrounding the planet, which allows the atmosphere to remain in place, rather than being blasted off the planet by solar winds.

[Mirioron]

Not only that - the outer core is also molten to a large degree. Without it, we wouldn't get such a strong dynamo effect.

[papito]

YES. A major one I forgot. This is the first thing I think about when I hear about colonizing Mars, which has no iron core to speak of.