Timeline for How could a planet have erratic days?
Current License: CC BY-SA 4.0
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| Jun 16, 2020 at 11:03 | history | edited | CommunityBot |
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| Mar 25, 2019 at 3:14 | comment | added | Vikki | "However note that, since chaotic rotation is not seen in objects that are spherically symmetric, it cannot happen on planets, which are, by definition, under hydrostatic equilibrium and thus spherically symmetric." Not quite - even a mostly-spherically-symmetric planet will still have mountains, craters, density variations, etc., that make it inevitably slightly asymmetric. Are planets highly resistant to chaotic rotation? Yes. Are they immune to it? Not completely. | |
| Mar 22, 2019 at 18:31 | comment | added | Dewi Morgan | @TheLuckless In long timescales, under gravity, planets are functionally liquids, not solids. Like droplets of matter. No object made of rock - no matter how "slowly" it accretes - can remain non-spherical past about 600km diameter. For ice, this is 400km. So, I agree with you that to have a non-spherical thing, you'd likely need a constructed planet, not a naturally-accreted one. This is called the "Potato radius" - see arxiv.org/pdf/1004.1091.pdf | |
| Mar 22, 2019 at 17:42 | comment | added | wizzwizz4 | @TheLuckless The definition of "planet" is fairly arbitrary. I don't think it mandates a spherical planet, but I think your thing wouldn't be in hydrostatic equilibrium and so wouldn't be considered a planet by the IAU. | |
| Mar 21, 2019 at 21:02 | comment | added | user22328 | This is the right answer. You can look at youtube.com/watch?v=tk8r85lM3SY and see the chaotic rotation nature | |
| Mar 21, 2019 at 19:02 | comment | added | TheLuckless | @ShadoCat I'm "Wrong" because you ignore my statement and apply an arbitrary rule that is based purely on what was observed in OUR solar system and how OUR solar system was formed, rather than how physics theoretically could allow a system to form? Nothing in physics would prevent an earth mass object from gathering slowly enough to not have a molten core - We just haven't observed it in the natural universe. But you would try to argue such an object Can't be considered a planet purely on the basis that it isn't 'round enough'? | |
| Mar 21, 2019 at 18:36 | comment | added | ShadoCat | @TheLuckless, Wrong. By definition, planets are spherical because they have enough mass to pull themselves to their center of mass. So, this cannot happen to a planet long term. For a short time, it can happen if the planet got hit by another planet but it won't be livable during that time either. | |
| Mar 21, 2019 at 18:02 | comment | added | Michael Macha | This is very helpful, but it's worth mentioning that the definition you're going by for planet is arbitrarily the IAU's definition—there's nothing binding about it, and nothing saying that a non-IAU-planet couldn't support life. It's more a terminology and communication thing. | |
| Mar 21, 2019 at 16:52 | comment | added | TheLuckless | To be fair there is a difference between "cannot", and "probably wouldn't happen in nature" - Under the right conditions and with the correct materials, you could potentially construct a planet with pockets of high density matter above the core such that you still get a roughly spherical surface. (Go really fancy with materials, temps, and pressures, and you might even be able to a 'pocket' that floats around in the mantle to really mess with rotational forces at the surface.) | |
| Mar 21, 2019 at 12:23 | history | answered | L.Dutch♦ | CC BY-SA 4.0 |