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Planet 9, Wherefore Art Thou?

Posted September 07, 2018 12:00 PM by HUSH
Pathfinder Tags: astronomy Planet 9 solar system
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Especially over the past year, it has been easy to get lost in all the buzzwords and publicity regarding outer space and astronomy. Zuma satellite failure! Missions to the moon, then Mars? SpaceX puts a Tesla in orbit! Illegal pirate satellites? Space Force! Russian military satellites? Hall thrusters!

Yet one of the most intriguing space stories has largely flown under the radar.

Pop quiz: How many major planets in the solar system?

  • If you said 8, congrats. You are technically correct (and on CR4 the best kind of correct).
  • If you said 9, let’s talk.

Remember Pluto was kicked from our solar systems models in 2006 after it was reclassified as a dwarf planet. (My childhood nostalgia still smarts from that.) Dwarf planets and minor planets “don’t count” for solar system purposes.

That said, there is growing evidence that there is another, dark planet on the outer reaches of the solar system. The planet has yet to be observed after two years of searching. This planet would have up to 10 times the mass of Earth, and could have a diameter four times as large.

The hypothesis for Planet 9 developed in 2014 and comes from astronomers Scott Shepard and Chad Trujillo. The orbits of the eight planets of the solar system are coplanar – each revolves around the sun along the same relative plane as a result of planet accretion from the swirling mass that begat our solar system. However, Shepard and Trujillo sought to explain why 90377 Sedna – a minor planet beyond Neptune – and several other bodies have an extremely eccentric orbit. Sedna lives beyond Pluto, and has longer oval-shaped orbit compared to the major planets. During their study, they determined that Neptunian gravitation pull could not be responsible for 12 trans-Neptunian objects (TNOs) with such eccentric orbits, with orbits roughly perpendicular to the orbital plane of the other planets.

A second peer study, conducted by Konstantin Batygin and Michael E. Brown from Caltech, eliminated some of the TNOs that they felt were influenced by Neptune. Of the remaining six objects, they also concluded that an unseen gravitational force was responsible for the unusual orbits. Since 2016, ten more TNOs have been discovered that add credence to the theory of Planet 9.

A Planet would also help explain some other system anomalies such as why TNO orbits are also roughly coplanar, or it could explain why the sun’s axis is tilted 6° when compared to the orbital plane of the eight known planets.

This all sounds easy enough, yet the planet hasn’t been observed via telescope. It only exists in mathematical models and computer simulations, likely in the direction of the constellations Cetus or Orion. The planet is unlikely to be seen even with the most power visible telescopes, although telescopes that measure radiation, such as ALMA, could perceive it. Even so, image recognition algorithms have been constructed to help comb data that has already be collected from the region where the planet is proposed to exist, and open-source projects for DIY astronomers invite users to look for it at home.

None of this enlightens on where Planet 9 came from or its unusual orbit. Explanations range from a planet that was ejected from the solar system proper due to a near-miss with a gas giant, capture of the planet from another solar system or as a free floating planet, or the possibility it coalesced on its own.

Supportive astronomers expect the planet to be found within the next few years. Whether or not it is actually out, this mystery is still unravelling. It has turned into a cosmic game of Where’s Waldo/Wally.

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#1

Re: Planet 9, Wherefore Art Thou?

09/07/2018 12:17 PM

It's also possible that it is some unknown phenomena...we don't know what we don't know...

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#2
In reply to #1

Re: Planet 9, Wherefore Art Thou?

09/07/2018 1:43 PM

Entirely valid. I perhaps should have added a note in the blog that not every astronomer is convinced Planet 9 is out there.

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#3

Re: Planet 9, Wherefore Art Thou?

09/07/2018 3:40 PM

Pluto was originally discovered because of irregularities in the orbits of Neptune and Uranus, the same way that Neptune had been located before it.

"American astronomer Percival Lowell first caught hints of Pluto's existence in 1905 from odd deviations he observed in the orbits of Neptune and Uranus, suggesting that another world's gravity was tugging at these two planets from beyond. Lowell predicted the mystery planet's location in 1915, but died without finding it. Pluto was finally discovered in 1930 by Clyde Tombaugh at the Lowell Observatory, based on predictions by Lowell and other astronomers."

https://www.space.com/43-pluto-the-ninth-planet-that-was-a-dwarf.html

Ironically, having been discovered in this way, Pluto was far too small to deviate the orbits of planets the size of Uranus and Neptune, leading to the conclusion that there is still more out there. Maybe more the work of Planet 9?

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#4

Re: Planet 9, Wherefore Art Thou?

09/07/2018 5:16 PM

From the article: It only exists in mathematical models and computer simulations, likely in the direction of the constellations Cetus or Orion.

This is pretty odd, actually. Orion and Cetus are not in the same part of the sky. Cetus is a large (wide) constellation, and the approximate 'center' is about 60 degrees from the 'center' of Orion. It's a bit like saying something is in the direction of Washington, DC or Boston, MA, while skipping over Baltimore, Philadelphia, and New York City.

Also, neither constellation contains the Ecliptic, the path in the sky along which most of the other planets are found. (Though the ecliptic passes near a corner of Cetus.)

All in all, this seems like a rather unimpressive guess for the possible planet's location.

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#7
In reply to #4

Re: Planet 9, Wherefore Art Thou?

09/07/2018 10:01 PM

Also, neither constellation contains the Ecliptic, the path in the sky along which most of the other planets are found.

Planet 9 is not supposed to be found in the ecliptic plane. Its orbit is thought to be about 30 degrees from the ecliptic plane.

As Planet 9 couples gravitationally to the Trans Neptunian Objects (TNOs) there is a transfer of angular momentum, causing a precession of the TNOs' orbits, much like the earth precesses due to tidal interaction.

https://en.wikipedia.org/wiki/Planet_Nine

One of the indications for the existence of Planet 9 that I've seen quoted is that the sun rotates in a plane that is 6 degrees from the ecliptic plane.

"Planet Nine—the undiscovered planet at the edge of the Solar System that was predicted by the work of Caltech's Konstantin Batygin and Mike Brown in January 2016—appears to be responsible for the unusual tilt of the sun, according to a new study.

The large and distant planet may be adding a wobble to the solar system, giving the appearance that the sun is tilted slightly.

"Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly twist out of alignment," says Elizabeth Bailey, a graduate student at Caltech and lead author of a study announcing the discovery.

All of the planets orbit in a flat plane with respect to the sun, roughly within a couple degrees of each other. That plane, however, rotates at a six-degree tilt with respect to the sun—giving the appearance that the sun itself is cocked off at an angle. Until now, no one had found a compelling explanation to produce such an effect. "It's such a deep-rooted mystery and so difficult to explain that people just don't talk about it," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

https://phys.org/news/2016-10-curious-tilt-sun-undiscovered-planet.html

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#10
In reply to #7

Re: Planet 9, Wherefore Art Thou?

09/08/2018 11:22 AM

Thanks.

This explains why they're not looking along the ecliptic per se, but it doesn't explain why they're looking at two regions so far apart.

And if they are looking at a region (or regions) 30 degrees from the ecliptic plane, it seems odd to be looking in Cetus which, as I mentioned, is close to the ecliptic plane.

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#12
In reply to #10

Re: Planet 9, Wherefore Art Thou?

09/08/2018 6:25 PM

"...why they're looking at two regions so far apart."

It's my "WA guess" that when they run the simulation, plugging in multiple locations for Planet 9, there are two positions that match the data with the highest probability. Just a guess, though.

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#13
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Re: Planet 9, Wherefore Art Thou?

09/08/2018 8:14 PM

And if they are looking at a region (or regions) 30 degrees from the ecliptic plane, it seems odd to be looking in Cetus which, as I mentioned, is close to the ecliptic plane.

The orbit of Planet 9 would lie in a plane passing through the sun. This plane would have to intersect the ecliptic plane (which also passes through the sun) in a line extending in two directions. These directions would be almost diametrically opposite from our viewpoint, given that earth's orbit is much closer to the sun than that of Planet 9.

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#14
In reply to #13

Re: Planet 9, Wherefore Art Thou?

09/09/2018 10:04 AM

Ok, so 'up to 30 degrees from the ecliptic plane'. That would make sense.

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#5

Re: Planet 9, Wherefore Art Thou?

09/07/2018 7:54 PM

Maybe it (Planet 9) hasn't been found yet because it is not a single planet but rather a disjunct swarm of dwarf planets from which Pluto is an escapee?

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#8
In reply to #5

Re: Planet 9, Wherefore Art Thou?

09/07/2018 10:28 PM

You stole my thunder dude, but good on you. My only addition is it (they) could be a number of swarms, I like the term flocks better, that given the ridiculously large transit circumference could co-exist on the same or near same orbital path.

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#6

Re: Planet 9, Wherefore Art Thou?

09/07/2018 9:02 PM

Neptune has an orbital period of 165 years. Pluto has an orbital period of 248 years but was only discovered 88 years ago. This makes me wonder if these orbital perturbations implying a ninth planet farther out than Pluto may just be orbital measurement uncertainties. On the other hand, wow that must be some incredibly accurate motion measurements of things very far away.

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#9

Re: Planet 9, Wherefore Art Thou?

09/07/2018 10:54 PM

This article is unfortunately biased in favor of one side in an ongoing debate. First, our solar system does NOT have only eight planets. The controversial demotion of Pluto by four percent of the IAU represents just one view among scientists, as an equal number of scientists rejected that definition in a formal petition. The latter prefer a geophysical planet definition that does not require an object to "clear its orbit" to be considered a planet. They therefore consider dwarf planets to be a subclass of planets, as intended by the scientists who first coined the term, New Horizons principal investigator Alan Stern. So yes, to many scientists, dwarf planets DO count as solar system planets. One of these scientists is Chad Trujillo, who as you note, in 2014 proposed the theory of an undiscovered outer solar system planet.

To scientists who prefer the equally legitimate geophysical planet definition, our solar system has 13 planets. Unfortunately, you failed to even mention that there is another side in this debate and treated the IAU definition as gospel truth, which it is not.

Neither Sedna nor any dwarf planets are "minor planets." That term refers to objects not large enough to be rounded by their own gravity, now designated by the IAU as "small solar system bodies."

The hypothesized but as yet undiscovered giant planet in the outer solar system should be called by the appropriate term for such an object, which is "Planet X," with "X" referring to the unknown, not to the number 10. Mike Brown deliberately chose the loaded, biased term "Planet 9" to promote his own agenda of having "killed" Pluto (he didn't) and to convey the false message that the entire scientific community agrees with him and views the solar system as having only eight planets, when this is far from the truth.

Recently, a group of planetary scientists issued a statement in the newsletter of the Planetary Science Institute requesting that the media, science community, and general public refer to this object by the fair and balanced term "Planet X." Please give serious consideration to their request.

There are several other possible objects that could have perturbed the small Kuiper Belt Objects in question. These could include a star that passed near the solar system a long time ago (the Sun did start its life in a cluster, whose stars later drifted apart), a brown dwarf that passed near the solar system, or even a rogue planet that did so.

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#11
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Re: Planet 9, Wherefore Art Thou?

09/08/2018 11:24 AM

Big thumbs up to this. Full of info that most people have never heard.

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#19
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Re: Planet 9, Wherefore Art Thou?

09/10/2018 9:28 PM

I have to agree with you, Planet 9 is a bad term. I always thought old Pluto got a bad rap. Using the term Planet X would isolate the totally unrelated matter of whether Pluto is a planet from the topic of this discussion, whether there is an unknown body influencing the motion of the members of the known solar system.

Some alien civilization might well consider only Jupiter, Saturn, Uranus, and Neptune as being significant enough to qualify as planets. We seem to feel that insignificant rocks like earth are important because we grew up here.

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#20
In reply to #9

Re: Planet 9, Wherefore Art Thou?

09/11/2018 8:49 AM

Biased? I don't agree with that. In fact, I think you are biased...

You've commented exactly twice on CR4 - the last 9 years ago - both attempts to discredit Mike Brown.

I was presenting a case for why some astronomers believe a Planet 9 is out there. As noted in previous comments, I should have stated in the main text that not all astronomers are on board with this idea. But getting into the minutiae of the debate is beyond the scope of this blog entry.

Second, the solar system has 8 known planets, per the IAU definition of a planet. Yes, there remains some controversy regarding the status of Pluto, as some other minor planets. But arguing that there are 13 accepted planets is a minority view of the solar system. Twist the argument far enough, and there are 750,000+ planets.

Third, Sedna is considered a dwarf planet. Dwarf planets are a type of minor planets.

It doesn't really matter what we call it, because it may or may not exist. In the media and casual astronomer circles, it is called Planet 9.

You also say that an IAU definition cannot be trusted, but cite the IAU later when it suits the argument. Which is it?

(mic drop)

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#21
In reply to #20

Re: Planet 9, Wherefore Art Thou?

09/11/2018 10:42 AM

There are several issues here. First, dwarf planets are NOT a type of minor planet. As Dr. David Weintraub notes in his book "Is Pluto A Planet?" the term "minor planet" is a synonym for asteroids and comets, objects not large enough or massive enough to be in hydrostatic equilibrium. Pluto does not belong in this category, as it is rounded by its own gravity and is geologically differentiated. Blurring the distinction between these two very different kinds of objects is simply bad science.

We need to drop the distinction between major vs. minor planets, which creates a false dichotomy. Instead, we should consider Alan Boyle's classification system, in which "planet" is a broad umbrella category under which there are numerous subcategories, including terrestrial, gas giant, ice giant, and dwarf planet.

The IAU definition is just one among several currently in use. It does not merit any form of preferential treatment above all other definitions currently in use. The claim that there are 13+ accepted planets in the solar system is in no way a minority view, as a majority of planetary scientists prefer the equally scientific geophysical definition, according to which dwarf planets are a subclass of planets – the meaning intended by Alan Stern when he first coined the term "dwarf planet" back in 1991.

Recently, some of these planetary scientists issued a formal request in the newsletter of the Planetary Science Institute that this hypothetical planet in the outer solar system be referred to by the traditional term "Planet X," as an acknowledgment that the number of solar system planets remains in dispute. This is how it should be referred to in the media and in circles of astronomy. Various writers and publications are now indicating that some scientists choose to call this hypothetical world "Planet X."

It is extremely doubtful that the solar system actually has 750,000 planets. However, the claim that it cannot have "too many planets" has no scientific basis and is not a "twisting" of any argument, especially the geophysical planet definition. If the solar system has 100 or 1,000 planets, then that is what it has. Kids don't need to memorize a list of names to learn about the solar system. That is an archaic method of teaching that goes back to a time when little was known about the planets other than their names. Instead, kids can be taught the different types of planets and their defining characteristics.

The only reason I cite the IAU definition is to illustrate the inconsistency in the arguments of some who support it. The IAU itself distinguished asteroids and comets (Small Solar System Bodies aka minor planets) from dwarf planets. Therefore, referring to dwarf planets as minor planets goes against their own definition.

Regarding Mike Brown, the only thing I am trying to discredit is his claim that he somehow "killed" Pluto, which is both unprofessional and untrue. He also states that the majority of planetary scientists agree with his position, which is not the case, and has even stated that scientists who support the geophysical definition do not really believe in it but are advocating it to support the New Horizons mission. Is he claiming he can read their minds? Furthermore, he is the one who chose the term "Planet 9," which he put in the title of the initial press release about this potential planet as a means of promoting his own agenda, that he "killed" Pluto and that the solar system has only eight planets. It was a slap in the face to all those who advocate the geophysical definition in place of the IAU one.

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#15

Re: Planet 9, Wherefore Art Thou?

09/10/2018 5:18 AM

Just a bit of pedantry:

"Wherefore" means why, not where.

Definition of wherefore

1 : for what reason or purpose : why 2 : therefore

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#16
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Re: Planet 9, Wherefore Art Thou?

09/10/2018 8:17 AM

"You are technically correct (and on CR4 the best kind of correct)."

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#17
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Re: Planet 9, Wherefore Art Thou?

09/10/2018 11:07 AM

I thought the answer to the question "Wherefore ?" is between three and five.

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#18
In reply to #17

Re: Planet 9, Wherefore Art Thou?

09/10/2018 11:14 AM

Can I get a rim shot?

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#22
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Re: Planet 9, Wherefore Art Thou?

09/11/2018 1:09 PM

Pa-dum!

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