Just a short post, since I do articles here from time to time to reassure those who worry about collisions with Earth for every new discovery. This new planet X is not even proved to exist yet. But if it is - it orbits way beyond Neptune. It is no more of a threat to us than Neptune was when it was discovered in the nineteenth century. Rather it's fun and exiting, and we could learn new things from it if it exists.
Artist’s rendering of what Planet Nine might look like.
Caltech/R. Hurt (IPAC)
This shows its orbit compared to the rest of the solar system:
(DATA) JPL; BATYGIN AND BROWN/CALTECH; (DIAGRAM) A. CUADRA/SCIENCE
Those images are from the Scientific American article.
At its closest it would be at least three times the distance to Neptune, or probably further than that from Earth. It is nothing at all like the Nibiru idea of a planet that comes into the inner solar system.
Here are some more articles about it if you want to go into it in depth:
Here on Science20: Planet Nine: Not Pluto, A New Planet Discovered In Our Solar System
BBC site: Case made for "ninth planet".
Skeptical article pointing out some issues with the idea that may need to be resolved:
Strong Evidence Suggests a Super Earth Lies beyond Pluto (Scientific American)
Also, our most sensitive wide field telescope able to search for planets at this distance, the Subaru telescope, has a decent chance of finding it if it exists.
The Subaru telescope, on Mount Kea in Hawaii, with a wide field of view and sensitive to faint sources, probably has best chance of spotting this new Planet X.
It could have been missed by WISE if near the furthest point of its orbit which is also where it would be most of the time since planets move much more quickly when closer to the sun. If it was at its closest to the sun, a Neptune sized object not much more than three times the distance to Neptune, we surely probably have spotted it by now.
IT'S A 3.8 SIGMA RESULT - SUGGESTIVE BUT NOT PROOF
Also though it is certainly an exciting discovery, just to say, it's not been proved yet, not nearly.
The chance it is just a coincidence, they make one in 15,000, or three sigma - the point where you think there may be something in it.
So, if you had just the one hypothesis ever, and got only a 1 in 15,000 chance that it doesn't exist, that's a near certainty.
But if you have thousands of astronomers searching for things then from time to time some of them are bound to hit on a 1 in 15,000 chance just by chance.
So you are bound to get a few results of similar probability to this from time to time. Though individually they seem very likely if you are the astronomer who came to this conclusion, when you take into account all the other astronomers looking and the number of hypotheses each one considers in a lifetime - it's not so impressive as it seems at first. That's why they are not saying "We have proved it", but are being professionally cautious about it, although it may seem at first like a near certainty. You might think they should just say it exists, with, on the face of it, a 99.993% certainty that it exists, but that's not how it works in science.
In particle physics, where the experiments generate huge amounts of data, 3 sigma results are common and are often just clusters, patterns in the noise. Collect enough data and you are bound to see 3 sigma results from time to time even if the data is random. They aim for 5 sigma for discovery.
“Others, like planetary scientist Dave Jewitt, who discovered the Kuiper belt, are more cautious. 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. That worries Jewitt, who has seen plenty of 3-sigma results disappear before. By reducing the dozen objects examined by Sheppard and Trujillo to six for their analysis, Batygin and Brown weakened their claim, he says. “I worry that the finding of a single new object that is not in the group would destroy the whole edifice,” says Jewitt, who is at UC Los Angeles. “It’s a game of sticks with only six sticks.””
Still it's intriguing and they claim it's the most likely planet X to date.
Note also that it is just an isolated planet. It's not a planet orbiting another star in our solar system, as is the idea for Nibiru. The idea of another star is pretty much ruled out now. Used to be thought that there could be a star Nemesis in a 26 million year orbit 1.5 light years from Earth. But though that's not completely ruled out, it's getting increasingly unlikely, and Tyche is also pretty much ruled out too, a similar star in a near circular orbit. If they did exist, they couldn't be any kind of a normal star, capable of keeping planets in orbit warm, not even a red dwarf. At most it's just possible there could be an exceptionally cold and dark brown dwarf out there bound to our solar system, but at least 0.41 light years away. But the chance of that is probably low.
LIMITS FROM THE WISE SURVEY
The original paper for the WISE results implications for planets is here:
The survey is for gas giants, and stars rather than terrestrial planets shining only by reflected light. It was an automated computer search with any tricky borderline cases investigated by hand.
The scans overlapped at the ecliptic poles. Each spot of the sky was photographed twelve times in the ecliptic, but hundreds of times at the poles. So there is no way it can miss planets that are out of the ecliptic - it is more sensitive to those than planets in the ecliptic.
Artist's impression of the Wide Field Infrared Survey Explorer which has produced the tightest constraints to date on Planet X.
It gives strong constraints on a Jupiter or Saturn sized object. A Jupiter sized object must be at least 82,000 au from the sun, and a Saturn sized object at least 28, 000 au. But a brown dwarf can actually be similar in size to Jupiter and also very cold and as well as that, it can be much darker than Jupiter in appearance (though not invisible in reflected light, - our Moon is as dark as worn asphalt and of course, easy to see).
Anyway, apparently it would be possible for a small, dark and very cold five billion year old brown dwarf to be in our solar system at a distance of 26,000 au, even closer than the limit for Saturn. But that's no use for Nibiru. That's 650 times the distance to Pluto, or 0.41 light years away - so far away it would take light over 21 weeks to get from the brown dwarf to Earth.
The survey could spot the more usual 150 K brown dwarf out to ten light years away. That's why the idea of an unseen star is getting increasingly unlikely. It couldn't have missed a red dwarf star, or any kind of a star at all. It just possibly could have missed a very dark brown dwarf in a Nemesis type orbit. But brown dwarfs are less common than they used to be thought to be. As a result of the WISE survey again, it's now thought that there are six normal stars for every brown dwarf.
Also it's not too surprising that our solar system turns out to have no companion star, not even a red dwarf - the majority (54%) of sun type stars are single. And a binary system is less likely to have stable planets, unless the companion is very distant, or very close to the sun. And what planets it has are more likely to be in very eccentric far from circular orbits, again unless the companion is very distant. So, given that we live on a planet with a stable near circular orbit - there's a selection bias in favour of non binary solar systems on top of that 54% result.
Constraints on dark matter in our solar system
By dark matter here the authors mean any form of matter not yet known including asteroids as well as the hypothetical "dark matter". So it's also relevant to things like "Nibiru".
Any matter inside of Saturn would be easy to spot from its gravitational effects on Mars, Saturn and the Earth. The reason they chose those three planets is because we have had Cassini in orbit around Saturn for years, and many spacecraft sent to Mars, and of course with Earth also - it means we have very precise measurements of their position in their orbits going back many years now.
Then, taking account of the effects of all the known matter in the solar system, they concluded that there is at most 1.7 ×10−10 M⊙ missing from the matter we know about inside of Saturn. That's unfamiliar units, for most of us, expressed in terms of the mass of the sun, which is 1.989 × 1030 kg
So this means we are missing at most 1.17 × 1020 kg. By comparison, the mass of Ceres is 8.958 × 1020 kg. So we are missing less than a seventh of the mass of Ceres.
To put it another way, if you had an asteroid with same density as Ceres, with this amount of mass, then its diameter would be 950*cube root(1.17/8.958) km or about 480 km in diameter.
So if all that matter was concentrated into a single object inside of Saturn's orbit, it can't be larger than about 480 km in diameter. Or if it was made of ice, it's diameter can't be larger than 950*cube root(2.161*1.17/8.958) km, or about 623 km in diameter
So there is no way that there are even any unknown large asteroids as large as Ceres inside of Saturn right now. If there were any, then we'd have spotted their effects on the orbits of Saturn, Mars and Earth through the sensitive position measurements we can do nowadays, no matter where they are.
When you get to the region inside of Jupiter, then as a result of the PAN-STARRS all sky survey for asteroids, we have a complete listing of all the asteroids of ten kilometers and larger. The only ones that could be not yet discovered are of order of one kilometer or so downwards. And we are discovering the one kilometer asteroids at one per month and have already found more than 90% of them.
For more on this see my "Imaginary Bullshit Planet" Nibiru - Lens Flares, Sun Mirages, Hoaxes&Just Plain SillyYou can also get it as a kindle booklet here:
You can read it on a kindle device, read it online in the Kindle cloud reader, or get the kindle app to read it on any device.
IF IT EXISTS, IS IT A PLANET ACCORDING TO THE IAU DEFINITION?
Some of the news reports I've seen have suggested it could be a planet according to the IAU definition - that it is massive enough to "clear its orbit".
But, how can it if it hasn't yet cleared out Sedna and the other dwarf planets that lead them to suspect it is there?
If they calculate that even Sedna is not enough matter to count for clearing its orbit (I haven't done the calculation) - still to prove it is a planet they would have to show that it has cleared out enough matter out to some huge distance beyond the Kuiper belt to count as clearing its orbit.
To establish that for sure would require a lot of observations even if it is true. They would have to do enough observations to establish the amount of matter in the entire region traversed by its orbit.
So the chances are we wouldn't know if it is a planet according to the IAU definition for decades, unless we prove that it isn't right away.
Looking a good many steps ahead - but could be as soon as within the next five years - if they find a celestial object the size of Neptune and it either does not "clear its orbit" according to the IAU definition, or they don't know yet if it does - what will they call it? They can't call it a planet.
So far they have called all objects that are in hydrostatic equilibrium (usually round, or ellipsoid if rapidly rotating,could in principle also be rocheworld contact binaries but not found any yet) - they call them all "Dwarf planets" if they don't clear their neighbourhood. And say they are not planets. But surely they won't call a Neptune sized object a "Dwarf planet".
It might lead to astronomers reconsidering the IAU defintion. Which I think, following Alan Stern, is a rather flawed definition not likely to last for long if we get new discoveries of large planets in the Kuiper belt or beyond as large as Mars or Earth or larger.
There are other comparatively minor flaws with the definition as well. It requires a planet to bein "hydrostatic equilibrium (nearly round)". But rapidly spinning objects in hydrostatic equilibrium can be triaxial ellipsoids, or even contact binary Rocheworld type "planets". Do those count as planets according to the IAU definition since they aren't by any stretch of the imagination "nearly round"?
This is the article I wrote about it:
And you might like my other posts on Quora
And on Science20
And I have many other booklets on my kindle bookshelf