IAA-CSIC: Haumea Has a Ring Around It

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IAA-CSIC: Haumea Has a Ring Around It

Postby bystander » Wed Oct 11, 2017 5:30 pm

Haumea, the Most Peculiar of Pluto Companions, Has a Ring Around It
Institute of Astrophysics of Andalusia - Superior Council of Scientific Investigations (IAA-CSIC) | 2017 Oct 11

The trans-neptunian belt contains four dwarf planets, among which Haumea stands out for its extremely elongated shape and rapid rotation. A stellar occultation makes it possible to establish main physical characteristics of heretofore this little known body – among which most surprising was presence of a ring

At the ends of the Solar System, beyond the orbit of Neptune, there is a belt of objects composed of ice and rocks, among which four dwarf planets stand out: Pluto, Eris, Makemake and Haumea. The latter is the least well known of the four and was recently the object of an international observation campaign which was able to establish its main physical characteristics. The study, led by astronomers from the Institute of Astrophysics of Andalusia and published in Nature, reveals the presence of a ring around the planet.

Trans-neptunian objects are difficult to study because of their small size, their low brightness, and the enormous distances that separate us from them. A very efficient but complex method lies in the study of stellar occultations, or the passing of these objects in front of a star (like a small eclipse). It allows astronomers to determine the main physical characteristics of an object (size, shape, and density) and has been successfully applied to dwarf planets Pluto, Eris and Makemake.

"We predicted that Haumea would pass in front of a star on the 21st of January 2017, and twelve telescopes from ten different European observatories converged on the phenomenon,” says José Luis Ortiz, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) in charge of the study. “This deployment of technical means allowed us to reconstruct with a very high precision the shape and size of dwarf planet Haumea, and discover to our surprise that it is considerably bigger and less reflecting than was previously believed. It is also much less dense than previously thought, which answered questions that had been pending about the object."

Haumea is an interesting object: it rotates around the Sun in an elliptic orbit which takes it 284 years to complete (it presently lies fifty times further from the Sun than the Earth), and it takes 3.9 hours to rotate around its axis, much less than any other body measuring more than a hundred kilometers long in the entire Solar System. This rotational speed causes it to flatten out, giving it an ellipsoid shape similar to a rugby ball. The recently published data reveal that Haumea measures 2.320 kilometers in its largest axis – almost the same as Pluto – but lacks the global atmosphere that Pluto has. ...

The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation - J. L. Ortiz et al
Last edited by bystander on Thu Oct 12, 2017 1:35 pm, edited 1 time in total.
Reason: Fixed link to paper
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Re: IAA-CSIC: Haumea Has a Ring Around It

Postby BDanielMayfield » Thu Oct 12, 2017 4:48 am

Wouldn’t such a rapid rotator’s shape be closer to a disc than to an elongated rugby ball?

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MPE: Ring around a Dwarf Planet Detected

Postby bystander » Thu Oct 12, 2017 2:21 pm

Ring around a Dwarf Planet Detected
Max Planck Institute for Extraterrestrial Physics | 2017 Oct 12

Ten observatories in six European countries teamed up for recent observations of a stellar occultation by the dwarf planet Haumea, which surprisingly show a narrow and dense ring orbiting the dwarf planet. In addition, the astronomers at the Max Planck Institute for Extraterrestrial Physics and more than 50 further institutions were able to constrain the size, shape and density of Haumea,which are closer to theoretical predictions than previous estimates but still puzzling. ...
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Re: IAA-CSIC: Haumea Has a Ring Around It

Postby neufer » Thu Oct 12, 2017 2:23 pm

BDanielMayfield wrote:
Wouldn’t such a rapid rotator’s shape be closer to a disc than to an elongated rugby ball?

Low angular momentum rotating liquid droplets, atomic nuclei and self gravitating bodies are always oblate spheroids.

High angular momentum rotating liquid droplets, atomic nuclei and self gravitating bodies are always prolate spheroids. (The atomic nuclei of the actinide elements are shaped like prolate spheroids.)

Very high angular momentum rotating liquid droplets, atomic nuclei and self gravitating prolate spheroids bifurcate into two separate objects.

https://en.wikipedia.org/wiki/Spheroid wrote:
Oblate spheroids

<<The oblate spheroid is the approximate shape of many planets and celestial bodies, including Saturn, Jupiter and the quickly-spinning star, Altair; in particular, cartographic and geodetic systems for the Earth are based on a reference ellipsoid.>>

Prolate spheroids

<<Several moons of the Solar system approximate prolate spheroids in shape, though they are actually triaxial ellipsoids. Examples are Mimas, Enceladus, and Tethys (satellites of Saturn) and Miranda (a satellite of Uranus).

In contrast to being distorted into oblate spheroids via rapid rotation, celestial objects distort slightly into prolate spheroids via tidal forces when they orbit a massive body in a close orbit. The most extreme example is Jupiter's moon Io, which becomes slightly more or less prolate in its orbit due to a slight eccentricity, causing spectacular volcanism. It should be noted that the major axis of the prolate spheroid does not run through the satellite's poles in this case, but through the two points on its equator directly facing toward and away from the primary.>>
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Re: IAA-CSIC: Haumea Has a Ring Around It

Postby MargaritaMc » Thu Oct 12, 2017 4:30 pm

BDanielMayfield wrote:Wouldn’t such a rapid rotator’s shape be closer to a disc than to an elongated rugby ball?

Bruce

This, below, from Wikipedia is - I think- rather what Neufer said above.
https://en.m.wikipedia.org/wiki/Haumea
Haumea displays large fluctuations in brightness over a period of 3.9 hours, which can only be explained by a rotational period of this length.[42] This is faster than any other known equilibrium body in the Solar System, and indeed faster than any other known body larger than 100 km in diameter.[15] While most rotating bodies in equilibrium are flattened into oblate spheroids, Haumea rotates so quickly that it is distorted into a triaxial ellipsoid. If Haumea were to rotate much more rapidly, it would distort itself into a dumbbell shape and split in two.[23] This rapid rotation is thought to have been caused by the impact that created its satellites and collisional family.[35]



The whole Wikipedia article is intriguing, including the discovery details.
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Re: IAA-CSIC: Haumea Has a Ring Around It

Postby MargaritaMc » Thu Oct 12, 2017 4:48 pm

I've just discovered that Wikipedia has a separate detailed examination of the contested discovery of Haumea in 2005, which involved Michael Brown of Caltech and the first named author of the current paper.
https://en.m.wikipedia.org/wiki/Controversy_over_the_discovery_of_Haumea
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Re: IAA-CSIC: Haumea Has a Ring Around It

Postby MarkBour » Tue Oct 17, 2017 11:25 pm

MargaritaMc wrote:
BDanielMayfield wrote:Wouldn’t such a rapid rotator’s shape be closer to a disc than to an elongated rugby ball?
Bruce

This, below, from Wikipedia is - I think- rather what Neufer said above.
https://en.m.wikipedia.org/wiki/Haumea
Haumea displays large fluctuations in brightness over a period of 3.9 hours, which can only be explained by a rotational period of this length.[42] This is faster than any other known equilibrium body in the Solar System, and indeed faster than any other known body larger than 100 km in diameter.[15] While most rotating bodies in equilibrium are flattened into oblate spheroids, Haumea rotates so quickly that it is distorted into a triaxial ellipsoid. If Haumea were to rotate much more rapidly, it would distort itself into a dumbbell shape and split in two.[23] This rapid rotation is thought to have been caused by the impact that created its satellites and collisional family.[35]

The whole Wikipedia article is intriguing, including the discovery details.

I am thinking we may never see a star or a gas giant in the shape of a prolate spheroid, without incredible forces involved (maybe if we see one approaching a supermassive black hole). For something like Haumea, I imagine that inside it are at least two dense regions that are at a distance from the center.

(This is just a personal view, after a brief reflection. Since I'm not an astronomer, I don't know if there is already some star that disproves my conjecture.)
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Re: IAA-CSIC: Haumea Has a Ring Around It

Postby neufer » Wed Oct 18, 2017 1:42 am

MarkBour wrote:
I am thinking we may never see a star or a gas giant in the shape of a prolate spheroid, without incredible forces involved.

Unstable convective gas with a hot dense core would not be conducive to forming a a prolate shape.
MarkBour wrote:
For something like Haumea, I imagine that inside it are at least two dense regions that are at a distance from the center.

Two dense regions that are at a distance from the center would not be conducive to Haumea remaining intact.

Self gravitating homogeneous rotating bodies start as oblate spheroids that transition into prolate ellipsoids as angular momentum increases.

This was all understood mathematically almost a century ago.
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Re: IAA-CSIC: Haumea Has a Ring Around It

Postby MargaritaMc » Wed Oct 18, 2017 11:08 am

neufer wrote:
This was all understood mathematically almost a century ago.


I'd be interested to know more, Art. Many thanks
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