IAA-CSIC: Haumea Has a Ring Around It

[bystander]

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

Artist concept of Haumea, with the correct proportions of the main body and the ring. The ring is at a distance of 2287 kilometers from the center of the main body and is darker than the surface of the dwarf planet itself. Credit: JM Madiedo, JL Ortiz

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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

• Nature 550(7675):197 (12 Oct 2017) DOI: 10.1038/nature24051

[BDanielMayfield]

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

Bruce

[bystander]

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. ...

[neufer]

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.

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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.

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.>>

[MargaritaMc]

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.

[MargaritaMc]

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/Controv ... _of_Haumea

[MarkBour]

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.)

[neufer]

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.

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.

[MargaritaMc]

This was all understood mathematically almost a century ago.

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

[MarkBour]

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.

Okay, forgive my hubris for my conjecture. And for even persisting a bit. But what would you expect was the history of this body? Do you view it as likely that the key event in its formation was a 2-body collision that merged the two bodies into a rapidly-rotating lump? And with that rapid of a rotation, would the two original cores likely merge into one? I would think they would remain distinct until something slowed the rotation. Would Haumea possibly have a molten or liquid core? That would encourage migration. Sorry, it's only by pushing like this that I'm learning. What do I know about planetary geology? Not much at all.

[BDanielMayfield]

Okay, forgive my hubris for my conjecture. And for even persisting a bit. But what would you expect was the history of this body? Do you view it as likely that the key event in its formation was a 2-body collision that merged the two bodies into a rapidly-rotating lump? And with that rapid of a rotation, would the two original cores likely merge into one? I would think they would remain distinct until something slowed the rotation. Would Haumea possibly have a molten or liquid core? That would encourage migration. Sorry, it's only by pushing like this that I'm learning. What do I know about planetary geology? Not much at all.

After reading the Wikipedia article on Haumea I’ll attempt answering Mark’s questions, since no one else has. Haumea likely formed as a normally round, normal rotating body composed mostly of ices billions of years ago along with objects similar to it such as Pluto. However, about 100 million years ago it suffered a glancing impact which gave it its spin, moons, a ring and a collisional family of smaller objects with similar orbits. The relatively recent date of this collision is inferred from the dwarf planet’s brightness and the spread of the collisional family’s orbits. Its odd shape would have developed naturally in response to the rapid rotation after the collision. There is no good reason to think that it should have either a double or a molten core since it is basically a clump of ices at about 50 degrees K.

Bruce

[neufer]

Okay, forgive my hubris for my conjecture. And for even persisting a bit. But what would you expect was the history of this body? Do you view it as likely that the key event in its formation was a 2-body collision that merged the two bodies into a rapidly-rotating lump? And with that rapid of a rotation, would the two original cores likely merge into one? I would think they would remain distinct until something slowed the rotation. Would Haumea possibly have a molten or liquid core? That would encourage migration. Sorry, it's only by pushing like this that I'm learning. What do I know about planetary geology? Not much at all.

After reading the Wikipedia article on Haumea I’ll attempt answering Mark’s questions, since no one else has. Haumea likely formed as a normally round, normal rotating body composed mostly of ices billions of years ago along with objects similar to it such as Pluto. However, about 100 million years ago it suffered a glancing impact which gave it its spin, moons, a ring and a collisional family of smaller objects with similar orbits. The relatively recent date of this collision is inferred from the dwarf planet’s brightness and the spread of the collisional family’s orbits. Its odd shape would have developed naturally in response to the rapid rotation after the collision. There is no good reason to think that it should have either a double or a molten core since it is basically a clump of ices at about 50 degrees K.

So...it was an ices attack

[MarkBour]

neufer: "ices attack?" Ouch. Well, in that case, we need to send some drones to the area.

BDanielMayfield: Thanks for explaining the ideas on Haumea's history. I had not noticed that there is a separate Wikipedia article devoted to the "collisional family". I'm just beginning to wonder about this topic, and the questions are coming like popping popcorn. But I'll read that and another article I've noticed referenced there, on "the scattered disc".

Part of my thinking about it came from Comet 67P. That still looks like a merger of two bodies to me. Of course it is much, much smaller.

One thing I was initially thinking is that a dwarf planet (or most anything larger than 1000km radius), if spherical, would likely have a dense core. I understand that our Moon does. Perhaps that is not the case for Haumea, and perhaps it is not the norm for the various dwarf-planet-sized bodies in our Solar system.

Another basic thing I'm wondering about the study of these objects. Watching them eclipse a star (clever technique). I'm just guessing here, but even at their small size and great distance, such events are still going to be more eclipses than transits, right? The typical angular size of these objects is still going to be greater than that of the star? I guess that is comparing 1000 km radius at 30 AU to something 1000 times larger in radius, but perhaps at 1000 light years distance. Not sure if it matters much, but it might affect what data can be gathered and how it is analysed. Detecting the ring around Haumea sounds like it might not have been that hard to notice. Detecting the elongated shape of Haumea would seem to be easier from a transit than an eclipse. It seems that in either case, multiple such events could steadily improve the data so gathered.

[neufer]

Click to play embedded YouTube video.

neufer: "ices attack?"

Ouch.

Well, in that case, we need to send some drones to the area.

[MargaritaMc]

I'm just beginning to wonder about this topic, and the questions are coming like popping popcorn.

I think it's great that you are having all these questions pop, Mark! I know the feeling. It's exciting and frustrating at the same time.
You might enjoy this marvellous (free) internet course, run by Mike Brown from Caltech.
https://www.coursera.org/learn/solar-system
I've taken it twice... It's not easy, but is SO worthwhile.
Here is the Intro video

Click to play embedded YouTube video.

Mike's blog is also worth digging into
http://www.mikebrownsplanets.com
He began it in 2007, so there's a lot of archives. (Here are a few entries about Haumea http://www.mikebrownsplanets.com/search/label/Haumea )

Happy popping!
Margarita

PS. Re one of your queries,

I'm just guessing here, but even at their small size and great distance, such events are still going to be more eclipses than transits, right?

this is from the opening post on this thread.

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).

[MarkBour]

Thank you, Margarita. It sounds like a marvelous course. I guess it is not available online at all times, but is offered next on January 1 (?)

I know that attached to APOD and Asterisk right here is Robert Nemiroff's astronomy course as well.

[MargaritaMc]

Thank you, Margarita. It sounds like a marvelous course. I guess it is not available online at all times, but is offered next on January 1 (?)

I know that attached to APOD and Asterisk right here is Robert Nemiroff's astronomy course as well.

Re Science of the Solar System - yes, I'd guess that's right. But one can enroll and they will notify you once the start date gets nearer. If you use Twitter, Mike also tends to let people know. (@plutokiller)

Re: Robert Nemiroff's course on YouTube - interestingly it was doing that course - which I found after hunting YouTube for "astronomy courses" - that alerted me of the existence of Apod and Asterisk.

There are other excellent astronomy education resources on the internet. If you want to know the ones I've worked though, contact me via private message.

[bystander]

Brazilian Scientists Investigate Dwarf Planet's Ring
São Paulo Research Foundation (FAPESP) | 2019 May 08

Theoretical paper published in MNRAS proposes an explanation for the dynamics of the ring around Haumea, a dwarf planet located beyond Pluto’s orbit (Image: NASA)

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Discovered in 2004, Haumea is a dwarf planet located beyond Pluto’s orbit in a region of the solar system called the Kuiper Belt. Pluto was demoted from the category of fully fledged planets in 2006 because of the discovery of Haumea and other dwarf planets.

Haumea was officially recognized as a dwarf planet in 2008. Its ellipsoidal shape resembles that of the ball used in rugby or American football. It has two moons and a ring. Because of its ring, Haumea is a member of a group of solar system objects comprising the planets Saturn, Uranus, Neptune and Jupiter, as well as the asteroids Chariklo and Chiron, which orbit between Jupiter and Neptune.

Haumea’s ring has never been directly observed. Its existence was inferred in 2017 by an international group of astronomers who took detailed measurements of the light fluctuations as Haumea occulted (passed in front of) a star. In space, an occultation occurs when one object passes in front of another from an observer’s perspective. ...

The researchers who discovered the ring in 2017 suggested that its orbit around Haumea was very close to the 1:3 resonance region, meaning that ring particles make one revolution every three times Haumea rotates.

A new study by Winter, Taís Ribeiro and Gabriel Borderes-Motta, who belong to UNESP’s Orbital Dynamics and Planetology Group, shows that a degree of eccentricity would be required for this resonance to act on the ring particles.

According to Winter, the fact that the ring is narrow and practically circular prevents action by the resonance. However, the group identified a specific type of stable, almost circular, periodic orbit in the same region as Haumea’s ring. A periodic orbit is an orbit that repeats over time. ...

On the Location of the Ring around the Dwarf Planet Haumea ~ O. C. Winter1, G. Borderes-Motta1, T. Ribeiro

• Monthly Notices of the RAS 484(3):3765 (Apr 2019) DOI: 10.1093/mnras/stz246
• arXiv.org > astro-ph > arXiv:1902.03363 > 09 Feb 2019