Imagine a planet, with two halves - one half of the crust & core rotating against the planetary rotation, remaining stable. The other half turns normaly similar to earth.

Could such a planet harbor life? Have a stable crust - besides a ring of magma along the equator? How would the intersections of oceans with the magma ocean influence the weather? How would a magnetic field or its absence work out? What bonuses and malis would such a setup have for inhabitants of such a world?

Could such a world survive to drift ocassionally out of the greenbelt ? Would it have constant earthquakes?

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    $\begingroup$ crust & core rotating against the planetary rotation,? What do you mean? $\endgroup$
    – L.Dutch
    Feb 12 at 11:54
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    $\begingroup$ I am highly skeptical of this concept from a mechanics point of view: earth rotates quickly and a natural "bearing" which can support the speed and load while remaining low-friction enough that it wouldn't simply stop after a bit is hard to envision. $\endgroup$
    – Dragongeek
    Feb 12 at 11:57
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    $\begingroup$ @Dragongeek... Even a man made bearing created with levels of precision impossible to imagine, out of a material 10x the durability of the strongest material we could make would fall apart on a geological/evolutionary scale. It would have millions of years of friction grinding it away... $\endgroup$
    – Questor
    Feb 12 at 23:19
  • $\begingroup$ Diamondshells, floating on a ocean of compressed unobtainium.. i get it $\endgroup$
    – Pica
    Feb 14 at 8:03

2 Answers 2


Sorry, but no. It would be absolutely impossible without magic. If such situation somehow developed, it would only last for a moment. Then, without magic, the halves would be in high-friction contact with each other. There is no way to keep them spinning independently.

The contact would make the halves friction weld like this glass. The faster spinning one would slow down while the slower-spinning one speeds up, and eventually they end up spinning the same speed, and then the seam between them would slowly start to cool down.

Until then, you have violent earthquakes all over the planet, and a wide glowing-hot area around the seam that will boil the waters away where the seam is, probably draining the oceans dry and making the whole planet a super-hot sauna. Everything would be dead except for extremophiles far enough from the seam.

  • $\begingroup$ Could this concept be salvaged? $\endgroup$
    – Pica
    Feb 12 at 13:42
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    $\begingroup$ You would need a magic, frictionless layer between the two halves. Like maybe a giant Larry-Niven-esque statis field in the shape of a disc that spans the whole equatorial plane and projects high enough past the surface to separate the counter-rotating atmospheres. $\endgroup$
    – Qami
    Feb 12 at 14:25
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    $\begingroup$ Yea, no. You couldn't even go with bearings and a solid core. The pressure would distort even the most durable of materials, converting the rotation into heat. Nice link to friction-welding glass, Jani! $\endgroup$ Feb 12 at 16:08
  • $\begingroup$ Can i accept two answers? $\endgroup$
    – Pica
    Feb 13 at 8:05
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    $\begingroup$ There shall be no war at dusk and dawn against the kingdom of eternal sunset living on the eye side of the planet $\endgroup$
    – Pica
    Feb 13 at 14:22

Exactly half of this idea is doable:

one half of the crust & core rotating against the planetary rotation

As the other answer explains, having the entire half of the planet rotating the wrong way would immediately grind to a halt due to the friction between the two halves. So we can't have the core part.

But the crust part - that would be doable if you were to give up on hard science. The crust has relatively little mass compared to the magma and all the other stuff above the core. With enough handwavium (but certainly less than you'd need to make two counter-rotating halves work) you could make different parts of the planetary crust rotate in different directions, or at least at different rates.

diagram of the planetary crust

This becomes a lot easier if the substrate is more malleable. For example, if your tectonic plates were more like sheets floating on water or air, rather than thick rock slabs floating in magma. Your mental model should be more like a gas giant than a rocky planet, where counter-rotating matter is par for the course.

enter image description here

And of course this all becomes much easier with a planet that rotates slowly. Earth is a spry young thing zipping along at 1 rotation every 24 hours. If you were looking at 1 rotation every year (a tidally locked planet) or even less frequently, you could get away with a lot more silly stuff.

At this point we are so far in the realm of contrivance that you could have whatever prevalent conditions you wanted on the surface. This is not a hard-science premise.

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    $\begingroup$ you're going to need a lot of handwavium to explain why friction between layers doesn't result in them rotating at the same rate (or at least a slowly and continuously varying one) $\endgroup$
    – Tristan
    Feb 13 at 11:50

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