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Researchers Find Evidence Of Distant Outer Planet
Mongo
post Jan 22 2016, 12:20 PM
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QUOTE (surbiton @ Jan 22 2016, 04:36 AM) *
Would that mean dear Pluto is back as a planet ? Whooopie !


Nope. Pluto is far too small to have any significant gravitational effect on other objects in similar orbits. It's merely one of numerous bodies of similar or slightly smaller size in its region of the Solar System, none of which are gravitationally significant. The dominant mass in its region is Neptune, which does control which orbits around it are occupied and which are empty, through resonances. The possible "Planet Nine", on the other hand, would count as a full planet because of its huge gravitational impact on everything in its region of the Solar System.
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scalbers
post Jan 22 2016, 05:38 PM
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On the other hand, planet 9 would be near the borderline of planethood, based on the graph we've seen in the 2015 Margot paper and in this blog:

http://www.findplanetnine.com/2016/01/is-p...ine-planet.html


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HSchirmer
post Jan 22 2016, 07:14 PM
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QUOTE (scalbers @ Jan 22 2016, 06:38 PM) *
On the other hand, planet 9 would be near the borderline of planethood, based on the graph we've seen in the 2015 Margot paper and in this blog:

http://www.findplanetnine.com/2016/01/is-p...ine-planet.html


The graph mentioned above illustrates an interesting point, " a planet clearing its orbit" IS actually a function of time AND mass. So the smaller bodies just take longer to BECOME planets.

It seems like Planet-9's current location would be the result of Jupiter or Saturn clearing IT out of THEIR orbit.
INSTABILITY-DRIVEN DYNAMICAL EVOLUTION MODEL OF A PRIMORDIALLY 5 PLANET OUTER
SOLAR SYSTEM
http://arxiv.org/pdf/1111.3682v1.pdf

Several runs of Nice Model simulations suggest that an ice giant between Saturn and Uranus would be the
most likely planet to be ejected.
Rather odd, then, that it WAS NOT a planet when it was being ejected from the orbital path of a gas giant,
then it becomes a planet when it clears out the area where it has been ejected to.
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JRehling
post Jan 22 2016, 07:26 PM
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This paper, Trujillo and Sheppard (2014), is so important to the discussion, that it should be read by anyone trying to understand the new work:

http://home.dtm.ciw.edu/users/sheppard/pub...heppard2014.pdf

It gives details of the key observation, that among minor planets with q>30 AU, the 12 objects with a>150 AU show common orbital characteristics that are not seen among the larger population of objects with q>30 AU and a<150 AU. 12 is sufficient to show statistical significance, so, simply put, there is something here that needs to be explained.

I think we need to see more work considering alternative explanations before a planetary perturber stands out as the only good explanation. Some things the two papers note:

1) Observational biases may exist, but can't explain all of the orbital similarities.
2) An origin based solely in the initial conditions of the outer solar system would not survive gigayear exposure to torques caused by the known outer planets.

Remaining models consist of various combinations of one or more perturbing objects orbiting the Sun combined possibly with some close stellar interaction in the past.

A difficulty is that the number of possible combinations of those models is wildly unconstrained. Finding a model that matches the observations pretty well isn't going to eliminate the infinite number of possible explanations that weren't considered. So, I think we're a long way from being able to duplicate the success of Neptune's discovery, where careful analysis gives astronomers a pinpoint location in the sky where the unseen object must exist.
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JRehling
post Jan 22 2016, 09:11 PM
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Funny, yet thought-provoking:

Possible Undiscovered Planets

http://xkcd.com/1633/
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vossinakis
post Jan 25 2016, 09:24 AM
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QUOTE (Gladstoner @ Jan 21 2016, 12:54 AM) *
I recall reading somewhere about an observed (possible) clustering of long-period cometary orbits that could have resulted from a distant massive planet or even a brown dwarf (which has since been ruled out). It would be interesting to compare these with the findings of Batygin-Brown.


Are you referring to this??? Arguments for the presence of a distant large undiscovered Solar system
planet http://astro.u-szeged.hu/ismeret/murray.pdf
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Floyd
post Jan 26 2016, 12:40 AM
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The latest Scientific American has an article on the search for planet X---by Michael Lemonick. Article good as background for this thread.


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TheAnt
post Jan 27 2016, 02:55 PM
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Oh yes I did run into that SciAm article also, before reading it I considered this to be one interesting idea but one that might have other explanations.
However when seeing this graphic with orbits of KBO's that are far from the ecliptic I began to understand why they find this such an tantalizing possibility.

Still when considering a planet like Neptune it should have an atmosphere that's gaseous even in the cold realm so far from the Sun. One such should show an IR excess for one or another reason, latent heat released when gas turning liquid and rain down for example. Now actually finding it might depend where this putative planet is located in its orbit, if it's anywhere of the furthest part of the orbit right now, the distance and very small proper motion might make it very difficult to detect. So yes, perhaps, they might be onto something here - yet, saying 'evidence' is stretching the meaning of the word a little bit to far yet. biggrin.gif
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jasedm
post Jan 27 2016, 07:03 PM
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I agree. Evidence there isn't (as yet)

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fredk
post Jan 27 2016, 09:04 PM
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Agreed. Possibly "indirect evidence" or "circumstantial evidence", with the caveat already mentioned here that an "unobvious bias" may also explain the observations. "Theoretical evidence" also doesn't make sense, since theories aren't observations and so can't provide evidence!

In my business, we'd probably call it a "hint".
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Habukaz
post Jan 27 2016, 11:00 PM
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It's easy for a definition of the word evidence to be circular:

a) evidence is something which shows that something exists
b) we know that something exists because we have evidence for its existence

So in order to know if something counts as evidence towards something, we first have to know if that something is real, and in order to know if something is real, we need evidence..


I think I'd rather put it this way: evidence is an observation consistent with a hypothesis, regardless of whether we assume the hypothesis to be true or false.

(now, you could say that evidence is part of what convinces you that something is real, but the subjectivity of this would make the definition problematic)

So I'd finally say that there is evidence - "inconclusive" evidence - for a fifth giant planet in the solar system. The consensus would also appear to be that not (good) enough evidence has been presented yet for this case in order to get really excited about it.


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Floyd
post Jan 27 2016, 11:45 PM
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We have the original data in the orbital parameters of several KBOs. Trying to explain the unusual clustering of these orbits, the idea of a 9th planet seemed a possibility. Much experimentation with computer modeling found a planet 9 mass and general orbit that could cause such clustering. Now there is a hypothesis. To test the hypothesis requires new data(KBOs) or spotting planet 9. The original data for a hypothesis can't be used as evidence for that hypothesis--must get new data.


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HSchirmer
post Jan 28 2016, 12:47 AM
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QUOTE (Habukaz @ Jan 27 2016, 11:00 PM) *
It's easy for a definition of the word evidence to be circular:
...
I think I'd rather put it this way: evidence is an observation consistent with a hypothesis, regardless of whether we assume the hypothesis to be true or false.
...


There are a few other definitions, the one I'm familiar with is logic/legal.

Evidence is anything that helps to prove or disprove an ultimate fact.

In much the same way that you have equations and variables, you also have law (hypothesis) and facts.
Facts are usually variables, unknowns that can be established or measured.
A series of facts, combined with an argument, eventually gets you to a proof.
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nprev
post Jan 28 2016, 01:39 AM
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MOD NOTE: Enough with the semantics, please.


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A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Gerald
post Jan 28 2016, 09:56 AM
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Citing this article:
QUOTE
The 0.007% chance that the clustering of the six objects is coincidental gives the planet claim a statistical significance of 3.8 sigma—beyond the 3-sigma threshold typically required to be taken seriously, but short of the 5 sigma that is sometimes used in fields like particle physics.

The range between 3 and 5 sigma is usually called "evident", greater or equal 5 sigma is called "definitive". 3 < 3.8 < 5. That's all.

The question is essentially, whether the numerical experimental settings leading to these 3.8 sigma confidence level are consistent with the way astronomers would have looked for the KBOs, hence whether the observational bias is considered appropriately.

One issue might be, that the same arguments preventing the direct observation of a possible planet 9 prevented observations of KBOs, e.g. the densely crowded Milky Way background.
Another issue might be an adjustment of the observation and detection methods to the first observed KBO of the presumed cluster. This disturbs the independence of the individual finds, as assumed in most randomized statistical tests, hence modifies inferred probabilities, and eventually the confidence level.

Edit: Another example: The probability of six objects randomly found in the same predefined 0.203 fraction of the sky is 7e-5 (the 3.8 sigma); the probability of six objects randomly found in the same predefined 0.379 fraction of the sky is 3e-3 (3.0 sigma). Hence another uncertainty is the size of the region of the sky the six observations are assigned to.
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