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Mercury and Venus are very near to being tidally locked, despite being thousands of times farther from the sun than the planet cited is from its star. Mars is a
by moloch-hai 4y ago
Mercury and Venus are very near to being tidally locked, despite being thousands of times farther from the sun than the planet cited is from its star. Mars is a good distance off.
Earth got its moon via a nearly, but not quite, fatal collision. Probably most other planets did not.
Ganymede's magnetic field is news to me. I don't think we know exactly what gives a body a magnetic field, or how it is maintained, but rotation seems to be important. Ganymede's is much, much weaker than ours, and some suggest it is a remnant frozen into rock.
- irq 4y ago> I don't think we know exactly what gives a body a magnetic field, or how it is maintained, but rotation seems to be important. The magnetic field on Earth is caused by electrical currents flowing in the rotating molten metal of the outer part of our planet’s core. You’re right, rotation is an important factor.
- mcv 4y agoI've long suspected that tidal forces from our moon may be a big factor in keeping the outer core liquid, and thereby keeping our magnetic field active. I have no idea if that's actually true, but if it is, both rotation and a large moon might be requirements for advanced life.
- moloch-hai 4y agoTidal forces from the sun are remarkably close in magnitude to those from our moon. Their chaotic interaction seems to me to interfere with any big, systematic effect on Earth's rotation. It seems possible that during certain times in the past, the lengths of the day and month (and year?) were in close enough resonance to accelerate loss of rotation for a while, until the change drove them back out of it .