APOD: Haumea of the Outer Solar System (2017 Oct 17)

[APOD Robot]

Haumea of the Outer Solar System

Explanation: One of the strangest objects in the outer Solar System has recently been found to have a ring. The object, named Haumea, is the fifth designated dwarf planet after Pluto, Ceres, Eris, and Makemake. Haumea's oblong shape makes it quite unusual. Along one direction, Haumea is significantly longer than Pluto, while in another direction Haumea has an extent very similar to Pluto, while in the third direction is much smaller. Haumea's orbit sometimes brings it closer to the Sun than Pluto, but usually Haumea is further away. Illustrated above, an artist visualizes Haumea as a cratered ellipsoid surrounded by a uniform ring. Originally discovered in 2003 and given the temporary designation of 2003 EL61, Haumea was renamed in 2008 by the IAU for a Hawaiian goddess. Besides the ring discovered this year, Haumea has two small moons discovered in 2005, named Hi'iaka and Namaka for daughters of the goddess.

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[Fevered]

Clicked on the "ring discovered" link, took me to a very curious looking dog. Is his name ring? Is he the discoverer of the ring? Inquiring minds want to know!

[bystander]

http://asterisk.apod.com/viewtopic.php?t=37651

[ta152h0]

just when you are convinced nothing else is possible the keeper of the universe decides to toy with humans

[neufer]

Clicked on the "ring discovered" link, took me to a very curious looking dog. Is his name ring? Is he the discoverer of the ring? Inquiring minds want to know!

---

<<Pete the Pup (original, 1924 – June 1930) was a character in Hal Roach's Our Gang comedies (later known as The Little Rascals) during the 1930s. Otherwise known as "Pete, the Dog With the Ring Around His Eye", or simply "Petey", he was well known for having a circled eye that was added on by Hollywood make-up artist Max Factor and credited as an oddity in Ripley's Believe It or Not. The original Pete (sired by "Tudor's Black Jack") was an American Pit Bull Terrier named "Pal the Wonder Dog", and had a natural ring almost completely around his right eye; dye was used to finish it off.>>

[Guest]

The ring made me wonder. Does a body require more than 1 moon to provide conditions for a ring to form? And rings seem to be pretty common in our solar system; Around big planets and the midgets too. Does the Earth not have a ring because we have less than 2 moons? I'm talking the celestial type of ring, not the bathtub type...

PS: If you don't want kids asking questions, just say so. Don't bust them over the head with 'silly anti spam bot questions'

[rstevenson]

... PS: If you don't want kids asking questions, just say so. Don't bust them over the head with 'silly anti spam bot questions'

The silly anti spam bot questions are not there to prevent children asking questions. They're there to prevent -- amazing coincidence! -- spam bots from littering the forum with spam, which they would happily do (if spam bots can be happy.)

Rob

[geckzilla]

... PS: If you don't want kids asking questions, just say so. Don't bust them over the head with 'silly anti spam bot questions'

The silly anti spam bot questions are not there to prevent children asking questions. They're there to prevent -- amazing coincidence! -- spam bots from littering the forum with spam, which they would happily do (if spam bots can be happy.)

It is also advisable to create a permanent account if one is going to continue posting at Asterisk. No more spam bot questions. BTW, it is quite challenging to come up with those questions. There are a lot of them that bots can solve instantly, but few that humans can solve and bots have trouble with.

[Chris Peterson]

The ring made me wonder. Does a body require more than 1 moon to provide conditions for a ring to form? And rings seem to be pretty common in our solar system; Around big planets and the midgets too. Does the Earth not have a ring because we have less than 2 moons? I'm talking the celestial type of ring, not the bathtub type...

We don't have a moon so much as we are a binary planet system. Our exceptionally large moon creates a very unstable environment around the Earth-Moon system, which has been observed to disrupt our capture of asteroids into stable orbits, and which certainly would disrupt a long term ring system. Rings don't like strong tides. It's also a problem that the Moon isn't in a circular orbit, and doesn't lie on our equatorial plane.

[neufer]

The ring made me wonder. Does a body require more than 1 moon to provide conditions for a ring to form? And rings seem to be pretty common in our solar system; Around big planets and the midgets too. Does the Earth not have a ring because we have less than 2 moons?

"Phobos will break up and form into a planetary ring in about 50 million years, because its low orbit with an orbital period that is shorter than a Martian day is decaying due to tidal deceleration." This will leave one ring & one moon.

<<It had previously been theorized by some astronomers that Pluto might have a ring system. However, this possibility has been ruled out by New Horizons, which would have detected any such ring system.

10199 Chariklo, a centaur, was the first minor planet discovered to have rings. It has two rings, perhaps due to a collision that caused a chain of debris to orbit it. The rings were discovered when astronomers observed Chariklo passing in front of the star UCAC4 248-108672 on June 3, 2013 from seven locations in South America. While watching, they saw two dips in the star's apparent brightness just before and after the occultation. Because this event was observed at multiple locations, the conclusion that the dip in brightness was in fact due to rings is unanimously the leading theory. The observations revealed what is likely a 19-kilometer-wide ring system that is about 1,000 times closer than the Moon is to Earth. In addition, astronomers suspect there could be a moon orbiting amidst the ring debris. If these rings are the leftovers of a collision as astronomers suspect, this would give fodder to the idea that moons (such as the Moon) form through collisions of smaller bits of material. Chariklo's rings have not been officially named, but the discoverers have nicknamed them Oiapoque and Chuí, after two rivers near the northern and southern ends of Brazil.

A second centaur, 2060 Chiron, is also suspected to have a pair of rings. Based on stellar-occultation data that were initially interpreted as resulting from jets associated with Chiron's comet-like activity, the rings are proposed to be 324 (± 10) km in radius. Their changing appearance at different viewing angles can explain the long-term variation in Chiron's brightness over time.

Ring systems may form around centaurs when they are tidally disrupted in a close encounter (within 0.4 to 0.8 times the Roche limit) with a giant planet. (By definition, a centaur is a minor planet whose orbit crosses the orbit(s) of one or more giant planets.) For a differentiated body approaching a giant planet at an initial relative velocity of 3−6 km/s with an initial rotational period of 8 hours, a ring mass of 0.1−10% of the centaur's mass is predicted. Ring formation from an undifferentiated body is less likely. The rings would be composed mostly or entirely of material from the parent body's icy mantle. After forming, the ring would spread laterally, leading to satellite formation from whatever portion of it spreads beyond the centaur's Roche Limit. Satellites could also form directly from the disrupted icy mantle. This formation mechanism predicts that roughly 10% of centaurs will have experienced potentially ring-forming encounters with giant planets.>>

[Rules For]

It's also a problem that the Moon isn't in a circular orbit, and doesn't lie on our equatorial plane.

I've long wondered why the Moon's orbit lies so much closer to the ecliptic than to the celestial equator, but I've had a difficult time finding explanations online. Does anybody here have any?

[Chris Peterson]

It's also a problem that the Moon isn't in a circular orbit, and doesn't lie on our equatorial plane.

I've long wondered why the Moon's orbit lies so much closer to the ecliptic than to the celestial equator, but I've had a difficult time finding explanations online. Does anybody here have any?

Well, why should it be on the equatorial plane? Satellite orbits are stable at any inclination.

Keep in mind, as well, that dynamically it's better to see the Moon in orbit around the Sun than the Earth. It experiences no epicycles; its orbital pattern around the Sun looks like an ellipse with little dimples every month. If the Earth just disappeared, the Moon would continue right along in practically the same orbit it's currently in. Just the dimples would disappear.

[Catalina]

It's also a problem that the Moon isn't in a circular orbit, and doesn't lie on our equatorial plane.

I've long wondered why the Moon's orbit lies so much closer to the ecliptic than to the celestial equator, but I've had a difficult time finding explanations online. Does anybody here have any?

Well, why should it be on the equatorial plane? Satellite orbits are stable at any inclination.

Keep in mind, as well, that dynamically it's better to see the Moon in orbit around the Sun than the Earth. It experiences no epicycles; its orbital pattern around the Sun looks like an ellipse with little dimples every month. If the Earth just disappeared, the Moon would continue right along in practically the same orbit it's currently in. Just the dimples would disappear.

I have never pondered that idea before--interesting. Is there a diagram illustrating the moon's solar orbit somewhere? Thanks Mr. Peterson.

[bystander]

I have never pondered that idea before--interesting. Is there a diagram illustrating the moon's solar orbit somewhere?

Click to play embedded YouTube video.

Be sure to watch it all.

[MarkBour]

<<Youtube video>>Be sure to watch it all.

This lovely animation is not what is happening, though. The moon is not getting closer to the Earth, it is getting farther away (currently, 3.8cm per year). https://en.wikipedia.org/wiki/Lunar_dis ... astronomy) Perhaps there was some reason for this animation to depict what it is showing, with the Moon spiraling in and colliding with the Earth..

[Chris Peterson]

<<Youtube video>>Be sure to watch it all.

This lovely animation is not what is happening, though. The moon is not getting closer to the Earth, it is getting farther away (currently, 3.8cm per year). https://en.wikipedia.org/wiki/Lunar_dis ... astronomy) Perhaps there was some reason for this animation to depict what it is showing, with the Moon spiraling in and colliding with the Earth..

That's not what it was showing. It was showing what the Moon's orbit looks like as you zoom outward to actual scale, and then what it looks like if you make the Earth go away. There was no collision, and none of the orbital distances were changing over the course of the animation.

[moontrail]

I miss in the lovely animation both earth and moon orbiting the center of masses of its binary system instead of moon just circling earth.
Ignacio

[Chris Peterson]

I miss in the lovely animation both earth and moon orbiting the center of masses of its binary system instead of moon just circling earth.

We wouldn't be able to see it at this scale. The distance from the Earth to the Moon is about 380 000 km. The Earth-Moon barycenter is less than 5 000 km from the center of the Earth (beneath the surface). That's just over 1% of the orbital radius of the Moon- at the scale of this video, less than a pixel. It's entirely possible the model used to create this video actually does have the two bodies orbiting around their barycenter.

[MarkBour]

<<Youtube video>>Be sure to watch it all.

This lovely animation is not what is happening, though. The moon is not getting closer to the Earth, it is getting farther away (currently, 3.8cm per year). https://en.wikipedia.org/wiki/Lunar_dis ... astronomy) Perhaps there was some reason for this animation to depict what it is showing, with the Moon spiraling in and colliding with the Earth..

That's not what it was showing. It was showing what the Moon's orbit looks like as you zoom outward to actual scale, and then what it looks like if you make the Earth go away. There was no collision, and none of the orbital distances were changing over the course of the animation.

Hmmm ... the video itself is not titled nor tagged with any explanation that I can see. (Title = "Lunar orbit around the Earth, as Earth orbits around the Sun".) Early in the video, the Moon's orbit clearly shows loops:

Later, the loops are shrinking, and one can see two blue circles drawn, with the one the Moon is "on" shrinking compared to the other one that I assumed was a reference to the earlier orbit:

In this third frame, the Moon is no longer making any loops, I think it is an epicycloid, but I don't really know the terms. You can clearly see it is way inside the blue circle:

Capture3.GIF (14.93 KiB) Viewed 6962 times

(continued ... Starship Asterisk does not seem to want to allow me a 4th image.)

[MarkBour]

Finally, what is the meaning of the red "X" ? If it is not a collision, then is it the point at which the Earth was "removed" ? I am then guessing that throughout the video the mass of the Earth was perhaps being steadily reduced to zero ?

But in that case, I'm not at all sure what physics was being calculated. If the mass of the Earth was being reduced, the orbits of Earth and Moon should have appeared equivalent at some point in time. And maybe they do, but only very near the end.

[Chris Peterson]

Finally, what is the meaning of the red "X" ? If it is not a collision, then is it the point at which the Earth was "removed" ? I am then guessing that throughout the video the mass of the Earth was perhaps being steadily reduced to zero ?

The "X" is when the Earth was removed. Otherwise, nothing was changing during the video except the scale factor (shown by the Earth-Moon distance). The actual orbit is what you see when the scale factor drops to one (the distance is just shown as 380 m.km.) That's what the lunar orbit around the Sun-Earth system looks like- a dimpled ellipse. Then the Earth is removed, and the Moon continues to follow the same orbit, just unperturbed by the Earth.

The loops/epicycles are just there at the beginning to emphasize what you can get with a three body system. They do not exist in the Earth-Moon-Sun system.

[Rules For]

Well, why should it be on the equatorial plane? Satellite orbits are stable at any inclination.

I don't know, other than that nearly all of the other major moons in the Solar System orbit very near to their planet's equatorial plane.

[alter-ego]

...
The loops/epicycles are just there at the beginning to emphasize what you can get with a three body system. They do not exist in the Earth-Moon-Sun system.

That certainly is the case. The animation is interesting to watch but a little confusing with scale and zoom changing together. It's clear that even the final orbit is not scaled correctly, most likely to show the wavy orbit more clearly. The displayed model used about 7 lunar orbits per year. There should be ~13.

Ignoring the barycenter, and assuming circular orbits, the trigonometry is straightforward to solve for the perturbed orbit. Below, I generated a correctly scaled orbit. You can just make out the "waviness", but it lacks the punch of the video's orbit because it's more subtle in reality. What might not be realized many is the orbit curvature changes in magnitude, but does not change sign, i.e. it's always bending towards the sun, unlike the more dramatic scallop/curly-Q orbits.

Lunar Orbit.PNG (5.87 KiB) Viewed 6890 times

[guest137]

It's also a problem that the Moon isn't in a circular orbit, and doesn't lie on our equatorial plane.

I've long wondered why the Moon's orbit lies so much closer to the ecliptic than to the celestial equator, but I've had a difficult time finding explanations online. Does anybody here have any?

Interesting discussion about absence of epicycles in the lunar orbit. Early in the history of the Earth-Moon system there likely would have been. The inner moons of Jupiter and Saturn should also show epicycles in plots like these. But Titan, with an orbit in Saturn's 'equitorial regeim' does not show epicycles.

Looking at the original question, I think that the term the poster wants to google is 'laplace plane'.

[moontrail]

I miss in the lovely animation both earth and moon orbiting the center of masses of its binary system instead of moon just circling earth.

We wouldn't be able to see it at this scale. The distance from the Earth to the Moon is about 380 000 km. The Earth-Moon barycenter is less than 5 000 km from the center of the Earth (beneath the surface). That's just over 1% of the orbital radius of the Moon- at the scale of this video, less than a pixel. It's entirely possible the model used to create this video actually does have the two bodies orbiting around their barycenter.

Thank you Chris, I took for granted that earth-moon system was much more binary than it really is.
Ignacio