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Basically what it says on the tin, I'm writing a fantasy world and I'm testing some exotic types of moons for this one. Then I came across Haumea, a dwarf planet located beyond Neptune.

Quoting Wikipedia:

This is faster than any other known equilibrium body in the Solar System, and in fact faster than any other known body over 100 km in diameter. [40] While most rotating bodies in equilibrium flatten into oblate spheroids, Haumea rotates so rapidly that it distorts into a triaxial ellipsoid. If Haumea spun much faster, it would distort into a dumbbell shape and split in two. [22] This rapid rotation is believed to have been caused by the impact that created its satellites and its family of collisions. [35]

Haumea is a triaxial ellipsoid, which means that all cross sections are ellipses and not circles. So hypothetically speaking, if a planet like earth had a moon shaped like Haumea, what would it look like from the planet? (Obviously this moon will have a similar rotation to that of Haumea to keep its shape.)

(ignore the moons and the ring around Haumea, I mean only its shape

Ignore the moons and the ring around Haumea, I mean only its shape

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    $\begingroup$ Haumea is fast rotating, Moon is tidally locked. Do you want to handwave tidal locking? $\endgroup$
    – Alexander
    Commented Jul 16, 2021 at 22:35
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    $\begingroup$ I already edited it. $\endgroup$
    – Xare
    Commented Jul 16, 2021 at 22:38
  • $\begingroup$ Well, it would look just like what you described - a triaxial ellipsoid, just as in the image. $\endgroup$
    – The Square-Cube Law
    Commented Jul 17, 2021 at 16:51
  • $\begingroup$ A minor problem is that we scientifically can't have fast rotating icy body in place of our Moon. A sufficiently advanced civilization may be able to place it there, but it won't stay in its initial state for long. $\endgroup$
    – Alexander
    Commented Jul 17, 2021 at 18:47
  • $\begingroup$ @Alexander maybe if you put the new moon on a canted orbit around Earth then place a solar shade on a halo orbit at L1, could keep it cool enough. You could also give the orbit a precession of 1 year such that the shadow of the new moon (and the shadow of the shade) never fall on Earth. $\endgroup$
    – BMF
    Commented Jul 17, 2021 at 19:25

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Its apparent size and brightness in the sky would fluctuate a couple to a few times every night.

sigh...

GIF is (...still?) broken, will try to fix later

Animated link

The minor planet has a rotational period of about 4 hours and is actually about as large as our moon: 2,100 × 1,680 × 1,074 km. (On it's long axis it's actually larger than the Moon!) At the moon's orbital distance, the visual changes would be most apparent to anyone on Earth.

Haumea has an albedo of 0.6-0.8 (whereas the Moon has an albedo of 0.12) due to its icy composition. It would be significantly brighter than the Moon, if it weren't for the fact that it would sublimate like the mother of all comets being so close to the Sun.

If you were to replace the volatile material of Haumea with the Moon's regolith and pockmark it with thousands of craters, it would effectively look like our Moon in the night sky (though just a bit smaller on average), stretching and squashing itself throughout the night. Any visible features would give away to any onlooker that it isn't actually changing shape, but is oddly shaped and rotating.

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  • $\begingroup$ I'm definitely adding a .gif file to my answer, but it seems to convert to a .jpg every time. Not sure how to fix it, but I'll include a link to the animated version. $\endgroup$
    – BMF
    Commented Jul 17, 2021 at 18:02
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    $\begingroup$ So, you're saying it would be the ultimate loading spinner. "Loading tomorrow..." $\endgroup$
    – Tom
    Commented Jul 17, 2021 at 19:54

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