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Planet Nine and the Nice Model

It looks like it’ll be another long, lonely autumn for Dr Mike Brown on the summit of the Hawaiian dormant volcano Mauna Kea, searching for Planet Nine.  He made use of the 8m Subaru telescope last year, and it looks like he’s back again this year for a second role of the dice (unless he does all this by remote control from Pasadena?).  I can only assume, given the time of the year, that the constellation of Orion remains high on their list of haystacks to search.

A recent article neatly sums up the current state of play with the hunt for Planet Nine (1), bringing together the various anomalies which, together, seem to indicate the presence of an undetected super-Earth some twenty times further away than Pluto (or thereabouts).  Given how much, I’ve written about this materials already, it seems unnecessary to go over the same ground.  I can only hope that this time, Dr Brown and his erstwhile colleague, Dr Batygin, strike lucky.  They have their sceptical detractors, but the case they make for Planet Nine still seems pretty solid, even if the gloss has come off it a bit recently with the additional OSSOS extended scattered disk object discoveries (2).  But there’s nothing on Dr Brown’s Twitterfeed to indicate what his plans are regarding a renewed search for Planet Nine.

Even if the Planet Nine article’s discussion about a new hunt for the celestial needle in the haystack is misplaced, it does make a valid point that super-Earths, if indeed that is what this version of Planet X turns out to be, are common enough as exo-planets, and weirdly absent in  our own planetary backyard.  So a discovery of such an object way beyond Neptune would satisfy the statisticians, as well as get the bubbly flowing at Caltech.  Dr Brown did seem to think that this ‘season’ would be the one.  We await with bated breath…

Meanwhile, the theoretical work around Planet Nine continues, with a new paper written by Konstantin Batygin and Alessandro Morbidelli (3) which sets out the underlying theory to support the result of the 2016 computer simulations which support the existence of Planet Nine (4).  Dr Morbidelli is an Italian astrophysicist, working in the south of France, who is a proponent of the Nice model for solar system evolution (named after the rather wonderful French city where he works).  This model arises from a comparison between our solar system’s dynamics, and those of the many other planetary systems now known to us, many of which seem bizarre and chaotic in comparison to our own.  Thus, the Nice model seeks to blend the kinds of dynamical fluctuations which might occur during the evolution of a star’s planetary system with both the outcomes witnessed in our own solar system, and the more extreme exoplanets observed elsewhere (5).  It invokes significant changes in the positions of the major planets during the history of the solar system, for instance.  These migrations have knock on effects which then drive other disturbances in the status quo of the early solar system, leading to the variations witnessed both here and elsewhere.  For instance, Dr Morbidelli lists one of the several factors which brought about the Nice model:
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Going the Wrong Way Round

A new Trans-Neptunian Object has been discovered whose quirkiness is breaking into new territory.  This object, currently named ‘Niku’ after the Chinese adjective for ‘rebellious’, is seriously off-piste and heading in a highly inclined, retrograde motion around the Sun (1).   Does this sound familiar?   The retrograde motion is something which Zecharia Sitchin claimed for the rogue planet Nibiru.  Niku…Nibiru.  It sounds like the team who discovered this object, based at the Harvard-Smithsonian Center for Astrophysics (2), are having a bit of fun with us.  Rest assured, this is not Nibiru, or anything like it.  That said, something in the past interacted with this object to fling it into its strange orbital path, and at the moment the identity of that strongly perturbing influence is a definitive ‘unknown‘.

Additionally, Niku’s discovery has prompted the astrophysics team to consider a new cluster of objects (high inclination TNOs and Centaurs) which appear to share the same orbital plane.  This, in itself, is an unexpected and exciting development.  Could the influencing factor be the mysterious Planet Nine (3)?

“…The new TNO appears to be part of another group orbiting in a highly inclined plane, so [Matthew] Holman’s team tested to see if their objects could also be attributed to the gravitational pull of Planet Nine.  It turns out Niku is too close to the solar system to be within the suggested world’s sphere of influence, so there must be another explanation. The team also tried to see if an undiscovered dwarf planet, perhaps similar to Pluto, could supply an explanation, but didn’t have any luck. “We don’t know the answer,” says Holman.” (1)

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